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'My fascination with meteorology and its related sciences stems from my love for remote sensing technology. This enthusiasm ignited in my youth when my father, a radiology doctor, showed me [...]

To conduct Time-varying Optical Measurements of Clouds and Aerosol Transport (TOMCAT), we present a novel mission concept that contrasts the historical large sensors in sun-synchronous orbit by combining active (lidar) [...]

Accurate measurements of ocean waves underpin efficient offshore operations and optimal offshore structure design, helping to ensure the offshore industry can operate both safely and economically. Popular instruments used by the offshore industry are the Rosemount WaveRadar (Radar) and the Waverider Buoy. The Optech Laser has been used at some locations for specific studies. Recent reports indicate systematic differences of order 10% among the wave measurements made by these instruments. This paper examines the relative performance of these instruments based upon various time-domain comparisons, including results from a quality control (QC) procedure, capabilities of measuring the wave surface profile (skewness), and crest heights for varying wind sea and swell conditions. The QC check provides good-quality data that can be further investigated with an assurance of error-free data, suggesting that the Waverider produces the bestquality data with the lowest failure rate compared to the Laser and Radar. A significant number of theWaverider surface elevation records have negative skewness, particularly at higher sea states, affecting its crest height measurements, which are lower than those from the Laser and Radar. Additionally, the significant wave height (H1/3) estimates of the Radar are lower than the Laser and Waverider, but its zero-crossing wave periods (TZ), on average, are longer than the Laser and theWaverider. The significant heights (H1/3) of Laser and Waverider are in good agreement for all three datasets, but the Waverider's zero-crossing wave period (TZ) estimates are significantly longer than the Laser. [ABSTRACT FROM AUTHOR]

ABSTRACT The Rapid Deployments to Wildfires Experiment (RaDFIRE) was a meteorological field campaign aimed at observing fire-atmosphere interactions during active wildfires. Using a rapidly deployable scanning Doppler lidar, airborne Doppler [...]

The operational light detection and ranging (lidar) data from the Hong Kong International Airport (HKIA) in China are assimilated in the six-nest, high-resolution Weather Research and Forecasting (WRF) Model. The existing radar data assimilation schemes in the WRF data assimilation (WRFDA) package have been adapted to accommodate the high temporal frequency and spatial resolution of the lidar observations. The weather data are then used to produce Lagrangian coherent structures to detect atmospheric hazards for flights. The coherent structures obtained from the various datasets are contrasted against flight data measured on aircraft. It is found that both WRF and WRFDA produce coherent structures that are more distinguishable than those obtained from two-dimensional retrieval, which may improve the detection of true wind shear hazards. [ABSTRACT FROM AUTHOR]

The first airborne wind measurements of a pulsed, 2- μm solid-state, high-energy, wind-profiling lidar system for airborne measurements are presented. The laser pulse energy is the highest to date in an eye-safe airborne wind lidar system. This energy, the 10-Hz laser pulse rate, the 15-cm receiver diameter, and dual-balanced coherent detection together have the potential to provide much-improved lidar sensitivity to low aerosol backscatter levels compared to earlier airborne-pulsed coherent lidar wind systems. Problems with a laser-burned telescope secondary mirror prevented a full demonstration of the lidar's capability, but the hardware, algorithms, and software were nevertheless all validated. A lidar description, relevant theory, and preliminary results of flight measurements are presented. [ABSTRACT FROM AUTHOR]

Special designed dual-Doppler setups can be used to retrieve simultaneous measurements of two wind components with high temporal resolution in several heights throughout the atmospheric boundary layer. During a field campaign in summer 2011, different scan strategies were performed to demonstrate the opportunities of obtaining variance profiles of the vertical and horizontal wind components in complex terrain. A simplified error analysis reveals the effects of the error propagation of the uncorrelated noise of the single lidar systems. A comparison shows that the course of the derived horizontal wind component is in accordance to in situ measurements. The dual-Doppler vertical wind velocity reflects the up- and downdrafts in a convective boundary layer and is even able to reflect a light rain event. The normalized profiles of the vertical velocity variances reproduce the well-known decrease from about one-third of the boundary layer height to its top. The horizontal velocity variance did not reveal a systematic behavior on the considered days. [ABSTRACT FROM AUTHOR]

Continuous sodar measurements of wind profiles have been carried out at the Zvenigorod Scientific Station of the Obukhov Institute of Atmospheric Physics since 2008. The station is located in a slightly inhomogeneous rural area about 45 km west of Moscow, Russia. The data were used to determine the parameters of wind and turbulence within low-level jets in the stable atmospheric boundary layer (ABL). Along with the mean velocity profiles, the profiles of variances of wind speed components from the sodar and the profiles of temperature from a microwave radiometer have been used to quantify turbulence and thermal stratification. Data from two sonic anemometers were used to get the near-surface parameters. The typical standard deviation of the vertical wind component σw within the low-level jet is about 5% of the maximum wind speed in the jet. No noticeable vertical variation of σw across the jets was detected in several earlier sodar campaigns, and it was not found in the present study. An increase in horizontal variances was detected in zones of substantial wind shear, which agrees with earlier published lidar data. Quasi-periodic structures in the sodar return signal, which appear in sodar echograms as braid-shaped patterns, were found to emerge preferably when a substantial increase of wind shear occurs at the top of the stable ABL. The braid patterns in the sodar echograms were not accompanied by any noticeable increase of observed σw, which disagrees with earlier data and indicates that such patterns may originate from various phenomena. [ABSTRACT FROM AUTHOR]

Pulsed Doppler lidars are powerful tools for long-range, high-resolution measurements of radial wind velocities. With the development of commercial Doppler lidars and the reduction of acquisition costs, dual-Doppler lidar systems will be become increasingly accessible in upcoming years. This study reviews the most common dual-Doppler techniques, describes the setup of a highly synchronized long-range dual-Doppler lidar system, and discusses extensively the different kinds of errors connected with this complex measurement technique. Sources of errors and their interactions are traced through the retrieval algorithm, including errors from single-Doppler lidar and those occurring from a combination of instruments related to various parameters, such as relative beam angles, time and spatial scales of the scan pattern, and atmospheric conditions. [ABSTRACT FROM AUTHOR]

Accurate measurements of cloud properties are necessary to document the full range of cloud conditions and characteristics. The Cloud, Aerosol Polarization and Backscatter Lidar (CAPABL) has been developed to address this need by measuring depolarization, particle orientation, and the backscatter of clouds and aerosols. The lidar is located at Summit, Greenland (72.6°N, 38.5°W; 3200 m MSL), as part of the Integrated Characterization of Energy, Clouds, Atmospheric State, and Precipitation at Summit Project and NOAA's Earth System Research Laboratory's Global Monitoring Division's lidar network. Here, the instrument is described with particular emphasis placed upon the implementation of new polarization methods developed to measure particle orientation and improve the overall accuracy of lidar depolarization measurements. Initial results from the lidar are also shown to demonstrate the ability of the lidar to observe cloud properties. [ABSTRACT FROM AUTHOR]

This study investigates the accuracy and calibration stability of temperature profiles derived from an operational Raman lidar over a 2-yr period from 1 January 2009 to 31 December 2010. The lidar, which uses the rotational Raman technique for temperature measurement, is located at the U.S. Department of Energy's Atmospheric Radiation Measurement site near Billings, Oklahoma. The lidar performance specifications, data processing algorithms, and the results of several test runs are described. Calibration and overlap correction of the lidar is achieved using simultaneous and collocated radiosonde measurements. Results show that the calibration coefficients exhibit no significant long-term or seasonal variation but do show a distinct diurnal variation. When the diurnal variation in the calibration is not resolved the lidar temperature bias exhibits a significant diurnal variation. Test runs in which only nighttime radiosonde measurements are used for calibration show that the lidar exhibits a daytime warm bias that is correlated with the strength of the solar background signal. This bias, which reaches a maximum of ~2.4 K near solar noon, is reduced through the application of a correction scheme in which the calibration coefficients are parameterized in terms of the solar background signal. Comparison between the corrected lidar temperatures and the noncalibration radiosonde temperatures show a negligibly small median bias of −0.013 K for altitudes below 10 km AGL. The corresponding root-mean-square difference profile is roughly constant at ~2 K below 6 km AGL and increases to about 4.5 K at 10 km AGL. [ABSTRACT FROM AUTHOR]

In this study several ice cloud retrieval products that utilize active and passive A-Train measurements are evaluated using in situ data collected during the Small Particles in Cirrus (SPARTICUS) field campaign. The retrieval datasets include ice water content (IWC), effective radius re, and visible extinction σ from CloudSat level-2C ice cloud property product (2C-ICE), CloudSat level-2B radar-visible optical depth cloud water content product (2B-CWC-RVOD), radar-lidar (DARDAR), and σ from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations ( CALIPSO). When the discrepancies between the radar reflectivity Ze derived from 2D stereo probe (2D-S) in situ measurements and Ze measured by the CloudSat radar are less than 10 dB Ze, the flight mean ratios of the retrieved IWC to the IWC estimated from in situ data are 1.12, 1.59, and 1.02, respectively for 2C-ICE, DARDAR, and 2B-CWC-RVOD. For re, the flight mean ratios are 1.05, 1.18, and 1.61, respectively. For σ, the flight mean ratios for 2C-ICE, DARDAR, and CALIPSO are 1.03, 1.42, and 0.97, respectively. The CloudSat 2C-ICE and DARDAR retrieval products are typically in close agreement. However, the use of parameterized radar signals in ice cloud volumes that are below the detection threshold of the CloudSat radar in the 2C-ICE algorithm provides an extra constraint that leads to slightly better agreement with in situ data. The differences in assumed mass-size and area-size relations between CloudSat 2C-ICE and DARDAR also contribute to some subtle difference between the datasets: re from the 2B-CWC-RVOD dataset is biased more than the other retrieval products and in situ measurements by about 40%. A slight low (negative) bias in CALIPSO σ may be due to 5-km averaging in situations in which the cirrus layers have significant horizontal gradients in σ. [ABSTRACT FROM AUTHOR]

This paper presents the motivation for, and initial results from, the Multiple Altimeter Beam Experimental lidar (MABEL) instrument. The MABEL instrument provides a new capability for airborne altimetry measurements and serves as a prototype and simulator for the upcoming NASA second-generation Ice, Cloud, and Land Elevation Satellite ( ICESat-2) mission. Designed to be highly flexible in measurement capability, MABEL serves as both a demonstration of measurement capability and a science tool for cryospheric and biospheric remote sensing. It is important to document the instrument specifications and essential background information to provide a suitable reference for the detailed MABEL results and science investigation publications that will be forthcoming. [ABSTRACT FROM AUTHOR]

Scanning Doppler lidar is a promising technology for improvements in short-term wind power forecasts since it can scan close to the surface and produce wind profiles at a large distance upstream (15-30 km) if the atmosphere has sufficient aerosol loading and there are no sizable blockages from terrain or large structures. However, successful measurements require a large spatial sampling domain and new estimation algorithms that can perform well in the very weak signal regime. The maximum likelihood (ML) algorithm in the spectral domain and a faster version based on the minimum mean-square-error (MSE) are investigated by numerical simulation and with actual scanning Doppler lidar data from the Lockheed Martin Coherent Technologies WindTracer lidar. In addition, the maximum range can be extended by simultaneous estimation of the wind speed and wind direction from a larger azimuth sector scan if the atmosphere is well behaved. Real-time operation is possible using the spectral data from the WindTracer lidar and a dedicated computer to interface with a data assimilation system. Analysis of the Doppler lidar data in the first few kilometers can be used to extract the turbulence conditions for improvements in real-time wind farm operations. [ABSTRACT FROM AUTHOR]

Field measurements of the wake flow produced from a 2-MW Enercon E-70 wind turbine were performed using three scanning Doppler wind lidars. A GPS-based technique was used to determine the position of the wind turbine and the wind lidar locations, as well as the direction of the laser beams. The lidars used in this study are characterized by a high spatial resolution of 18 m, which allows the detailed characterization of the wind turbine wake. Two-dimensional measurements of wind speed were carried out by scanning a single lidar over the vertical symmetry plane of the wake. The mean axial velocity field was then retrieved by averaging 2D scans performed consecutively. To investigate wake turbulence, single lidar measurements were performed by staring the laser beam at fixed directions and using the maximum sampling frequency. From these tests, peaks in the velocity variance are detected within the wake in correspondence of the turbine top tip height; this enhanced turbulence could represent a source of dangerous fatigue loads for downstream turbines. The spectral density of the measured velocity fluctuations shows a clear inertial-range scaling behavior. Then, simultaneous measurements with two lidars were performed in order to characterize both the axial and the vertical velocity components. For this setup, the two velocity components were retrieved only for measurement points for which the two laser beams crossed nearly at a right angle. Statistics were computed over the sample set for both velocity components, and they showed strong flow fluctuations in the near-wake region at turbine top tip height, with a turbulence intensity of about 30%. [ABSTRACT FROM AUTHOR]

This study illustrates the high potential of RALI, the French airborne radar-lidar instrument, for studying cloud processes and evaluating satellite products when satellite overpasses are available. For an Arctic nimbostratus ice cloud collected on 1 April 2008 during the Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols, and Transport (POLARCAT) campaign, the capability of this synergistic instrument to retrieve cloud properties and to characterize the cloud phase at scales smaller than a kilometer, which is crucial for cloud process analysis, is demonstrated. A variational approach, which combines radar and lidar, is used to retrieve the ice-water content (IWC), extinction, and effective radius. The combination of radar and lidar is shown to provide better retrievals than do stand-alone methods and, in general, the radar overestimates and the lidar underestimates IWC. As the sampled ice cloud was simultaneously observed by CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations ( CALIPSO) satellites, a new way to assess satellite cloud products by combining in situ and active remote sensing measurements is identified. It was then possible to compare RALI to three satellite ice cloud products: CloudSat, CALIPSO, and the Cloud-Aerosol-Water-Radiation Interactions (ICARE) center's radar-lidar project (DARDAR). [ABSTRACT FROM AUTHOR]

Ground-based sensing of wind profiles by sodars and lidars is becoming the standard for wind energy and other applications. However, there remain difficulties in complex terrain since the instruments sense wind components in spatially separated volumes, and systematic spatial variations of the wind components can lead to systematic bias in wind estimation. The errors are typically less than 6%, so corrections do not need to be very sophisticated. Analytic potential flow models are developed for the flow over a bell-shaped hill and over an escarpment. These models are then used to find the radial Doppler shift from sampling volumes in typical sodar and lidar beam geometries, thereby allowing spatial variation bias to be removed. Since the models are straightforward, bias removal is readily achieved, and also lends itself to an understanding of the significant parameters affecting wind errors. The bell model is tested against field data from sodars and lidars in both moderately complex and in very complex terrain. It is found that corrected winds are to within approximately 1% of those measured by mast instruments. Much more complex models do not correct wind errors better than these simple models. [ABSTRACT FROM AUTHOR]

A ground-based lidar system that has been deployed in Whistler, British Columbia, Canada, since the spring of 2010 provides a means of evaluating vertical aerosol structure in a mountainous environment. This information is used to help to determine when an air chemistry observatory atop Whistler Mountain (2182 m MSL) is within the free troposphere or is influenced by the valley-based planetary boundary layer (PBL). Three case studies are presented in which 1-day time series images of backscatter data from the lidar are analyzed along with concurrent meteorological and air-chemistry datasets from the mountaintop site. The cases were selected to illustrate different scenarios of diurnal PBL evolution that are expected to be common during their respective seasons. The lidar images corroborate assumptions about PBL influence as derived from analysis of diurnal trends in water vapor, condensation nuclei, and ozone. Use of all of these datasets together bolsters efforts to determine which atmospheric layer the site best represents, which is important when evaluating the provenance of air samples. [ABSTRACT FROM AUTHOR]

A coherent 2-µm differential absorption and wind lidar (Co2DiaWiL) with a 2-µm single-frequency Q-switched laser with laser frequency offset locking was used for long-range CO2 measurement. The frequency stabilization of the single-frequency λ on pulsed laser was 1.0 MHz. Experimental horizontal CO2 measurement over a column range of 2.6-5.6 km and 900 shot pairs (1-min integration time) was conducted on 22 October 2009 to examine the detection sensitivity of the Co2DiaWiL. The achieved precision was less than 2.1%. The root-mean-square of the differences between the 30-min CO2 averages measured by the Co2DiaWiL and a ground-based in situ instrument was 0.9% (3.5 ppm). Experimental vertical CO2 measurements were conducted in February 2010 and January and February 2011. The partial CO2 column-averaged dry-air mixing ratios (XCO2) for an altitude between 0.4 and 1.0 km in 2010 and 2011 were 403.2 ± 4.2 and 405.6 ± 3.4 ppm, respectively. In the paper, the Co2DiaWiL results were well validated carefully against those of the airborne in situ instrument; they agreed well within the margin of error. The values of XCO2 measured in presence of cirrus clouds near the tropopause (hard target cases) show a difference of less than 4.1 ppm with the airborne measurements performed on 14 February 2010. This result demonstrates the capability of the Co2DiaWiL to measure XCO2 within a precision better than 1%. [ABSTRACT FROM AUTHOR]

A chirped laser pulse can introduce artifacts into datasets of coherent Doppler wind lidars. At close vicinity of strong signal peaks undesired artificial velocities can be measured and continuous signals can be shifted by a constant factor. It is shown how to remove these artifacts and how to retrieve accurate velocity estimations from both clouds and the planetary boundary layer. Therefore, a two-dimensional deconvolution technique is applied to the wind lidar datasets in order to correct the chirp effect in the range and frequency space. The chirp correction for a 1-h measurement of vertical velocities in the atmosphere is presented. The method is applied to the averaged Doppler spectra. Therefore, no access to the raw heterodyne signal is necessary. The complexity of the data acquisition software and the amount of data to be stored is hereby significantly reduced. Simulations suggest that the remaining velocity error resulting from the laser pulse chirp is smaller than 0.02 m s−1 and chirp-induced artifacts are removed reliably. The method also increases the signal resolution in the range and frequency dimension and can be applied for this intent even if there is no chirp. [ABSTRACT FROM AUTHOR]

A new ground-based wind profiling technology-a scanned bistatic sodar-is described. The motivation for this design is to obtain a 'mastlike' wind vector profile in a single atmospheric column extending from the ground to heights of more than 200 m. The need for this columnar profiling arises from difficulties experienced by all existing lidars and sodars in the presence of nonhorizontally uniform wind fields, such as found generically in complex terrain. Other advantages are described, including improved signal strength from turbulent velocity fluctuations, improved data availability in neutral atmospheric temperature profiles, improved rejection of rain echoes, and improved rejection of echoes from fixed (nonatmospheric) objects. Initial brief field tests indicate that the scattered intensity profile agrees with theoretical expectations, and bistatic sodar winds are consistent with winds from standard mast-mounted instruments. [ABSTRACT FROM AUTHOR]

The estimation of sensible heat flux, H, using large aperture scintillometer (LAS) under varying surface heterogeneity conditions was investigated. Surface roughness features characterized by variable topography and vegetation height were represented using data derived from the highly accurate light detection and range (lidar) techniques as well as from traditional vegetation survey and topographic map methods. The study was conducted at the Cibola National Wildlife Refuge, Southern California, over a riparian zone covered with natural vegetation dominated by tamarisk trees interspersed with bare soil in a region characterized by arid to semiarid climatic conditions. Estimates of H were obtained using different representations of surface roughness features derived from both traditional and lidar methods to estimate LAS beam height [ z( u)] at each increment u along its path, vegetation height ( hc), displacement height ( d), and roughness length ( z0) combined with the LAS weighing function, W( u), along the path. The effect of the LAS 3D footprint was examined to account for the contribution from the individual patches in the upwind direction, hence on the estimates of H. The results showed better agreement between LAS and Bowen ratio sensible heat fluxes when lidar-derived surface roughness was used, especially when considering the LAS 3D footprint effects. It was also found that, under certain conditions, the LAS path weighted hc and d obtained using the LAS weighting function W( u) is a good approximation of the 3D weighted footprint values. [ABSTRACT FROM AUTHOR]

Three-dimensional winds obtained with an airborne Doppler lidar are used to investigate the spatial structure of topographically driven flows in complex coastal terrain in Southern California. The airborne Doppler lidar collected four hours of data between the surface and 3000 m MSL along a 40-km segment of the Salinas Valley during the afternoon of 12 November 2007. The airborne lidar measurements, obtained at horizontal and vertical resolutions of approximately 1500 and 50 m, respectively, reveal a detailed spatial structure of the atmospheric flows within the valley and their associated aerosol features. Clear skies prevailed on the flight day with northwesterly synoptic flows around 10 m s−1. The data document a shallow sea breeze making a transition into an upvalley flow in the Salinas Valley that accelerates in the upvalley direction. Along with the acceleration of the upvalley wind, the lidar data indicate the presence of enhanced sinking motions. No return flows associated with the sea-breeze or upvalley flows are observed. While synoptic flows are aligned along the valley axis in the upvalley direction, lidar data indicate the presence of a northerly cross-valley flow around the height of the surrounding ridges. This flow intrudes into the valley atmosphere and induces, along with thermally driven slope flows on the sunlit valley sidewall, a cross-valley circulation that causes an asymmetric distribution of the aerosols. This study demonstrates the large potential of airborne Doppler lidar data in describing flows in complex terrain. [ABSTRACT FROM AUTHOR]

The naive Bayesian methodology has been applied to the challenging problem of cloud detection with NOAA's Advanced Very High Resolution Radiometer (AVHRR). An analysis of collocated NOAA-18/AVHRR and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations ( CALIPSO)/Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations was used to automatically and globally derive the Bayesian classifiers. The resulting algorithm used six Bayesian classifiers computed separately for seven surface types. Relative to CALIPSO, the final results show a probability of correct detection of roughly 90% over water, deserts, and snow-free land; 82% over the Arctic; and below 80% over the Antarctic. This technique is applied within the NOAA Pathfinder Atmosphere's Extended (PATMOS-x) climate dataset and the Clouds from AVHRR Extended (CLAVR-x) real-time product generation system. Comparisons of the PATMOS-x results with those from International Satellite Cloud Climatology Project (ISCCP) and Moderate Resolution Imaging Spectroradiometer (MODIS) indicate close agreement with zonal mean differences in cloud amount being less than 5% over most zones. Most areas of difference coincided with regions where the Bayesian cloud mask reported elevated uncertainties. The ability to report uncertainties is a critical component of this approach. [ABSTRACT FROM AUTHOR]

NASA A-Train vertical profilers provide detailed observations of atmospheric features not seen in traditional imagery from other weather satellite data. CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations ( CALIPSO) profiles vividly depict the vertical dimension of otherwise two-dimensional features shown in mapped products. However, most forecasters have never seen these profiles and do not appreciate their capacity to convey fundamental information about cloud and precipitation systems. Here, these profiles are accompanied by weather satellite images and explained in the context of various meteorological regimes. Profile examples are shown over frontal systems, marine stratocumulus, orographic barriers, tropical cyclones, and a severe thunderstorm. [ABSTRACT FROM AUTHOR]

The Stratospheric Aerosol and Gas Experiment II (SAGE II) aerosol products from 1998 to 2004 have been analyzed for the tendency of changes in background stratospheric aerosol properties. The aerosol extinction coefficient E has apparently increased in the midlatitude lower stratosphere (LS) in both hemispheres, at an annual rate that is as great as 2%%-5%%. Positive changes in the aerosol surface area density S in the midlatitude LS are most distinct, with a rate of increase that is as high as 5%%-6%% annually. At the same time, there has been a secular decrease in aerosol effective radius R, especially in the tropical LS, at a rate of up to −2.5%% yr−1. Corresponding to these trends, the aerosol number concentration is inferred to have increased by roughly 5%%-10%% yr−1 in the tropical LS and by 4%%-8%% yr−1 in the midlatitude LS. Changes in aerosol mass are also deduced, with rates of increase in the midlatitude LS that are in the range of 1%%-5%% yr−1. The large uncertainty in operational S product is the major factor influencing the trend in S, aerosol number concentrations, and mass. The authors' global assessment supports the speculation of Hofmann et al. on the basis of local observations that the cause of an increase in lidar backscatter over a similar period was a consequence of aerosol particle growth due to enhanced anthropogenic sulfur dioxide emissions. Moreover, it is found that an increase in the injection rate of condensation nuclei from the troposphere to the stratosphere at tropical latitudes is required to sustain the increase in stratospheric aerosol concentrations identified in this analysis. [ABSTRACT FROM AUTHOR]

Long-range lidar systems have been used operationally at the Hong Kong International Airport for wind shear alerting. They are used for monitoring the headwinds over the last 3 n mi of all of the runway corridors of the Hong Kong International Airport (HKIA). This paper discusses the results of a trial of using short-range lidar (SRL) in the alerting of wind shear over a particular runway corridor by performing more frequently updated wind measurements over a specific section of this corridor in which many wind shear reports are received. The radial resolution of the lidar is 75 m and the data are updated every 20 s. Three different ways of wind shear alerting based on SRL's data are studied, namely, the deviations of the measured radial velocities from the uniform background flow (the 'velocity fluctuation'), eddy dissipation rate (EDR), and autocorrelation of radial velocity. The performance of these methods is studied by comparing with the pilot wind shear reports. The velocity fluctuation has the best skill in capturing the wind shear reports. By combining the wind shear alerts from SRL with those from the Wind Shear and Turbulence Warning System (WTWS), it is possible to achieve a probability of detection (POD) of pilot wind shear reports of about 90%%, with a percentage of time on alert (PTA) of about 10%% only. This even outperforms the existing overall wind shear alerting service (WTWS plus subjective wind shear warnings issued by aviation weather forecasters) by significantly reducing PTA. As such, the present study shows that it is possible to combine wind shear alerts from SRL and WTWS for automatic wind shear alerting without the need of human intervention, at least for a particular runway corridor of HKIA. [ABSTRACT FROM AUTHOR]

A Rayleigh-Mie-Raman lidar has been installed and is operating in the Polar Environment Atmospheric Research Laboratory at Eureka in the High Arctic (79°59′N, 85°56′W) as part of the Canadian Network for the Detection of Atmospheric Change. The lidar operates in both the visible and ultraviolet and measures aerosol backscatter and extinction coefficients, depolarization ratio, tropospheric temperature, and water vapor mixing ratio. Variable field of view, aperture, and filtering allow fine-tuning of the instrument for different atmospheric conditions. Because of the remote location, operations are carried out via a satellite link. The instrument is introduced along with the measurement techniques utilized and interference filter specifications. The temperature dependence of the water vapor signal depends on the filter specifications, and this is discussed in terms of minimizing the uncertainty of the water vapor mixing ratio product. Finally, an example measurement is presented to illustrate the potential of this instrument for studying the Arctic atmosphere. [ABSTRACT FROM AUTHOR]

Liquid clouds play a profound role in the global radiation budget, but it is difficult to retrieve their vertical profile remotely. Ordinary narrow-field-of-view (FOV) lidars receive a strong return from such clouds, but the information is limited to the first few optical depths. Wide-angle multiple-FOV lidars can isolate radiation that is scattered multiple times before returning to the instrument, often penetrating much deeper into the cloud than does the single-scattered signal. These returns potentially contain information on the vertical profile of the extinction coefficient but are challenging to interpret because of the lack of a fast radiative transfer model for simulating them. This paper describes a variational algorithm that incorporates a fast forward model that is based on the time-dependent two-stream approximation, and its adjoint. Application of the algorithm to simulated data from a hypothetical airborne three-FOV lidar with a maximum footprint width of 600 m suggests that this approach should be able to retrieve the extinction structure down to an optical depth of around 6 and a total optical depth up to at least 35, depending on the maximum lidar FOV. The convergence behavior of Gauss-Newton and quasi-Newton optimization schemes are compared. Results are then presented from an application of the algorithm to observations of stratocumulus by the eight-FOV airborne Cloud Thickness from Off-Beam Lidar Returns (THOR) lidar. It is demonstrated how the averaging kernel can be used to diagnose the effective vertical resolution of the retrieved profile and, therefore, the depth to which information on the vertical structure can be recovered. This work enables more rigorous exploitation of returns from spaceborne lidar and radar that are subject to multiple scattering than was previously possible. [ABSTRACT FROM AUTHOR]

Linear features in a clear convective boundary layer (CBL) over the North Atlantic Ocean were studied during a weak cold air outbreak using a down-looking airborne lidar. Sequential lidar profiles were placed together and color coded to provide images of aerosol and molecular scattering from below the aircraft to the ocean surface, over a 36-km segment of a flight track approximately 150 km off the coast of southern Virginia. The aircraft flew on a path approximately perpendicular to the expected orientation of cloud streets if they had formed. The lidar image clearly shows randomly sized convective cells in the CBL, grouping under the crests of a gravity wave in the stable troposphere. It is suggested that the wave develops as energetic convective cells in the CBL penetrate into the stable layer aloft and act as obstructions to the relative flow. An analytic study, published in 1965, demonstrates that vertical disturbances on the top of the CBL adjust to be in resonance with a horizontal gravity wave in the free troposphere. The results of the study along with an interpretation of the lidar images have led to the development of a simple conceptual model that is used to estimate the spacing and orientation of long linear convective features in the midlatitude CBL. In addition, the conceptual model can explain the change in cloud street patterns with increasing fetch, seen in satellite images. Comparisons with observations from this study and five other midlatitude field programs show good agreement. A suggestion for future research is presented. [ABSTRACT FROM AUTHOR]

During stable nighttime periods, large variations in temperature and visibility often occur over short distances in regions of only moderate topography. These are of great practical significance and yet pose major forecasting challenges because of a lack of detailed understanding of the processes involved and because crucial topographic variations are often not resolved in current forecast models. This paper describes a field and numerical modeling campaign, Cold-Air Pooling Experiment (COLPEX), which addresses many of the issues. The observational campaign was run for 15 months in Shropshire, United Kingdom, in a region of small hills and valleys with typical ridge-valley heights of 75-150 m and valley widths of 1-3 km. The instrumentation consisted of three sites with instrumented flux towers, a Doppler lidar, and a network of 30 simpler meteorological stations. Further instrumentation was deployed during intensive observation periods including radiosonde launches from two sites, a cloud droplet probe, aerosol monitoring equipment, and an instrumented car. Some initial results from the observations are presented illustrating the range of conditions encountered. The modeling phase of COLPEX includes use of the Met Office Unified Model at 100-m resolution, and some brief results for a simulation of an intensive observation period are presented showing the model capturing a cold-pool event. As well as aiding interpretation of the observations, results from this study are expected to inform the design of future generations of operational forecasting systems [ABSTRACT FROM AUTHOR]

Shallow-angle lidar offers an attractive approach to acquiring spatial profiles of sea waves, which are of value in both oceanographic research and practical engineering applications, such as in the control of wave energy capture devices and for a variety of vessel operations. However, the wave elevation values produced by shallow-angle lidar are inevitably nonuniformly distributed in space and, given that most processing algorithms require uniformly sampled data, an equivalent set of uniformly distributed data must be derived from the lidar measurements. A new class of algorithm is introduced to achieve this goal and applied to experimental shallow-angle lidar data. Compared to traditional methods the new approach has advantages in terms of both computational cost and the degree of nonuniformity that can be accommodated. [ABSTRACT FROM AUTHOR]

From a weather forecasting perspective, the Arctic poses particular challenges for mainly two reasons: 1) The observational data are sparse and 2) the weather phenomena responsible for severe weather, such as polar lows, Arctic fronts, and orographic influences on airflow, are poorly resolved and described by the operational numerical weather prediction (NWP) models. The Norwegian International Polar Year (IPY)- The Observing System Research and Predictability Experiment (THORPEX) project (2007-10) sought to significantly improve weather forecasts of these phenomena through a combined modeling and observational effort. The crux of the observational effort was a 3-week international field campaign out of northern Norway in early 2008, combining airborne and surface-based observations. The main platform of the field campaign was the Deutsches Zentrum für Luft- und Raumfahrt (DLR) research aircraft Falcon, equipped with lidar systems for profiling of aerosols, humidity, and wind, in addition to in situ measurements and dropsondes. A total of 12 missions were flown, yielding detailed observations of polar lows, Arctic fronts, and orographic low-level jets near Spitsbergen, the coast of northern Norway, and the east coast of Greenland. The lidar systems enabled exceptionally detailed measurements of orographic jets caused by the orography of Spitsbergen. Two major polar low developments over the Norwegian Sea were captured during the campaign. In the first polar low case, three f lights were carried out, providing a first-ever probing of the full life cycle of a polar low. Targeting observations by the aircraft in sensitive areas led to improvements in predicted track and intensity of the polar low. Here highlights from the field campaign, as well as from ongoing follow-up investigations, are presented. Highlights from the development of a new limited-area model ensemble prediction system for the Arctic, as well as an exploitation of new satellite data [[Infrared Atmospheric Sounding Interferometer (IASI) data]], are also included. [ABSTRACT FROM AUTHOR]

The NOAA airborne ozone lidar system [Tunable Optical Profiler for Aerosol and Ozone (TOPAZ)] is compared with the fast-response chemiluminescence sensor flown aboard the NOAA WP-3D during the 2006 Texas Air Quality Study (TexAQS). TOPAZ measurements made from the NOAA Twin Otter, flying at an altitude of ~3300 m MSL in the Houston, Texas, area on 31 August, and the Dallas, Texas, area on 13 September, show that the overall uncertainty in the 10-s (~600-m horizontal resolution) TOPAZ profiles is dominated by statistical uncertainties (1 σ) of ~8 ppbv (6%%-10%%) at ranges of ~2300 m from the aircraft (~1000 m MSL), and ~11-27 ppbv (12%%-30%%) at ranges of ~2800 m (~500 m MSL). These uncertainties are substantially reduced by spatial averaging, and the averages of 11 profiles (of 110 s or 6.6-km horizontal resolution) at ~1000 m MSL are in excellent agreement (±2%%) with the in situ measurements at ~500 m MSL. The TOPAZ measurements at lower altitudes on 31 August exhibit a negative bias of up to ~15%%, however, when the lidar signals were strongly attenuated by very high ozone levels in the plume from the Houston Ship Channel. This bias appears to result from nonlinear behavior in the TOPAZ signal amplifiers, which is described in the companion paper by Alvarez et al. An empirical correction is presented. [ABSTRACT FROM AUTHOR]

The National Oceanic and Atmospheric Administration/Earth System Research Laboratory/Chemical Sciences Division (NOAA/ESRL/CSD) has developed a versatile, airborne lidar system for measuring ozone and aerosols in the boundary layer and lower free troposphere. The Tunable Optical Profiler for Aerosol and Ozone (TOPAZ) lidar was deployed aboard a NOAA Twin Otter aircraft during the Texas Air Quality Study (TexAQS 2006) and the California Research at the Nexus of Air Quality and Climate Change (CalNex 2010) field campaigns. TOPAZ is capable of measuring ozone concentrations in the lower troposphere with uncertainties of several parts per billion by volume at 90-m vertical and 600-m horizontal resolution from an aircraft flying at 60 m s−1. The system also provides uncalibrated aerosol backscatter profiles at 18-m vertical and 600-m horizontal resolution. TOPAZ incorporates state-of-the-art technologies, including a cerium-doped lithium calcium aluminum fluoride (Ce:LiCAF) laser, to make it compact and lightweight with low power consumption. The tunable, three-wavelength UV laser source makes it possible to optimize the wavelengths for differing atmospheric conditions, reduce the interference from other atmospheric constituents, and implement advanced analysis techniques. This paper describes the TOPAZ lidar, its components and performance during testing and field operation, and the data analysis procedure, including a discussion of error sources. The performance characteristics are illustrated through a comparison between TOPAZ and an ozonesonde launched during the TexAQS 2006 field campaign. A more comprehensive set of comparisons with in situ measurements during TexAQS 2006 and an assessment of the TOPAZ accuracy and precision are presented in a companion paper. [ABSTRACT FROM AUTHOR]

A new measurement capability has been implemented in the Arctic Lidar Technology (ARCLITE) system at the Sondrestrom upper-atmosphere research facility near Kangerlussuaq, Greenland (67.0°N, 50.9°W), enabling estimates of atmospheric water vapor through the troposphere. A balloon campaign was simultaneously conducted to calibrate and validate the new lidar water vapor measurements. Initial results show that height-resolved profiles up to 10 km with better than 10%% error are obtained with 30-min integration and 250-m height resolution. Comparison of the lidar observations with water vapor profiles retrieved by the Atmospheric Infrared Sounder (AIRS) instrument on board the Aqua satellite agree within the error associated with each measurement. These new observations offer more routine measurements of water vapor in the Arctic to complement measurements related to the Arctic's hydrologic cycle. [ABSTRACT FROM AUTHOR]

Accurate knowledge of cloud optical properties, such as extinction-to-backscatter ratio and depolarization ratio, can have a significant impact on the quality of cloud extinction retrievals from lidar systems because parameterizations of these variables are often used in nonideal conditions to determine cloud phase and optical depth. Statistics and trends of these optical parameters are analyzed for 4 yr (2003--07) of cloud physics lidar data during five projects that occurred in varying geographic locations and meteorological seasons. Extinction-to-backscatter ratios (also called lidar ratios) are derived at 532 nm by calculating the transmission loss through the cloud layer and then applying it to the attenuated backscatter profile in the layer, while volume depolarization ratios are computed using the ratio of the parallel and perpendicular polarized 1064-nm channels. The majority of the cloud layers yields a lidar ratio between 10 and 40 sr, with the lidar ratio frequency distribution centered at 25 sr for ice clouds and 16 sr for altocumulus clouds. On average, for ice clouds the lidar ratio slightly decreases with decreasing temperature, while the volume depolarization ratio increases significantly as temperatures decrease. Trends for liquid water clouds (altocumulus clouds) are also observed. Ultimately, these observed trends in optical properties, as functions of temperature and geographic location, should help to improve current parameterizations of extinction-to-backscatter ratio, which in turn should yield increased accuracy in cloud optical depth and radiative forcing estimates. [ABSTRACT FROM AUTHOR]

Modeling of the systematic errors in the second-order moments of wind speeds measured by continuous-wave (ZephIR) and pulsed (WindCube) lidars is presented. These lidars use the conical scanning technique to measure the velocity field. The model captures the effect of volume illumination and conical scanning. The predictions are compared with the measurements from the ZephIR, WindCube, and sonic anemometers at a flat terrain test site under different atmospheric stability conditions. The sonic measurements are used at several heights on a meteorological mast in combination with lidars that are placed on the ground. Results show that the systematic errors are up to 90%% for the vertical velocity variance, whereas they are up to 70%% for the horizontal velocity variance. For the ZephIR, the systematic errors increase with height, whereas for the WindCube, they decrease with height. The systematic errors also vary with atmospheric stability and are low for unstable conditions. In general, for both lidars, the model agrees well with the measurements at all heights and under different atmospheric stability conditions. For the ZephIR, the model results are improved when an additional low-pass filter for the 3-s scan is also modeled. It is concluded that with the current measurement configuration, these lidars cannot be used to measure turbulence precisely. [ABSTRACT FROM AUTHOR]

Seven atmospheric density current fronts are identified in sequences of ground-based, scanning aerosol backscatter lidar images and in situ micrometeorological time series data that were collected simultaneously and nearly continuously between 15 March and 11 June of 2007 in Dixon, California. The fronts, observed on different days, had the following features in common: 1) an increase in aerosol backscatter intensity, 2) a decrease in air temperature, 3) an increase in water vapor mixing ratio, 4) movement toward the north, 5) airflow from the south in the denser air mass, and 6) occurrence within a 3.5-h time span in the afternoon. The observations support the hypothesis that the fronts are the leading edges of shallow marine air masses advancing northward from the Sacramento--San Joaquin River Delta. The observations are used to test an empirical relationship between front speed, airmass density difference, depth of the dense air mass, and speed of the opposing flow. Prominent features of the fronts such as lobe and cleft structure, billows, and nose and head structure are described. Time-lapse animations of the lidar scans are available in the online version of this article. [ABSTRACT FROM AUTHOR]

Seven atmospheric density current fronts are identified in sequences of ground-based, scanning aerosol backscatter lidar images and in situ micrometeorological time series data that were collected simultaneously and nearly continuously between 15 March and 11 June of 2007 in Dixon, California. The fronts, observed on different days, had the following features in common: 1) an increase in aerosol backscatter intensity, 2) a decrease in air temperature, 3) an increase in water vapor mixing ratio, 4) movement toward the north, 5) airflow from the south in the denser air mass, and 6) occurrence within a 3.5-h time span in the afternoon. The observations support the hypothesis that the fronts are the leading edges of shallow marine air masses advancing northward from the Sacramento--San Joaquin River Delta. The observations are used to test an empirical relationship between front speed, airmass density difference, depth of the dense air mass, and speed of the opposing flow. Prominent features of the fronts such as lobe and cleft structure, billows, and nose and head structure are described. Time-lapse animations of the lidar scans are available in the online version of this article. [ABSTRACT FROM AUTHOR]

Coordinated observational data of atmospheric aerosols were collected over a 24-h period between 2300 mountain daylight time (MDT) on 27 August 2009 and 2300 MDT on 28 August 2009 at Bozeman, Montana (45.66°°N, 111.04°°W, elevation 1530 m) using a collocated two-color lidar, a diode-laser-based water vapor differential absorption lidar (DIAL), a solar radiometer, and a ground-based nephelometer. The optical properties and spatial distribution of the atmospheric aerosols were inferred from the observational data collected using the collocated instruments as part of a closure experiment under dry conditions with a relative humidity below 60%%. The aerosol lidar ratio and aerosol optical depth retrieved at 532 and 1064 nm using the two-color lidar and solar radiometer agreed with one another to within their individual uncertainties while the scattering component of the aerosol extinction measured using the nephelometer matched the scattering component of the aerosol extinction retrieved using the 532-nm channel of the two-color lidar and the single-scatter albedo retrieved using the solar radiometer. Using existing aerosol models developed with Aerosol Robotic Network (AERONET) data, a thin aerosol layer observed over Bozeman was most likely identified as smoke from forest fires burning in California; Washington; British Columbia, Canada; and northwestern Montana. The intrusion of the thin aerosol layer caused a change in the atmospheric radiative forcing by a factor of 1.8 ±± 0.5 due to the aerosol direct effect. [ABSTRACT FROM AUTHOR]

The vertical profiling of CO2 turbulent fluxes in the atmospheric boundary layer (ABL) is investigated using a coherent differential absorption lidar (CDIAL) operated nearby a tall tower in Wisconsin during June 2007. A CDIAL can perform simultaneous range-resolved CO2 DIAL and velocity measurements. The lidar eddy covariance technique is presented. The aims of the study are (i) an assessment of performance and current limitation of available CDIAL for CO2 turbulent fluxes and (ii) the derivation of instrument specifications to build a future CDIAL to perform accurate range-resolved CO2 fluxes. Experimental lidar CO2 mixing ratio and vertical velocity profiles are successfully compared with in situ sensors measurements. Time and space integral scales of turbulence in the ABL are addressed that result in limitation for time averaging and range accumulation. A first attempt to infer CO2 fluxes using an eddy covariance technique with currently available 2- μμm CDIAL dataset is reported. [ABSTRACT FROM AUTHOR]

The Canadian CloudSat/Cloud--Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) Validation Project (C3VP) was designed to acquire aircraft, surface, and satellite observations of particle size distributions during cold season precipitation events for the purposes of validating and improving upon satellite-based retrievals of precipitation and the representation of cloud and precipitation processes within numerical weather prediction schemes. During an intensive observation period on 22 January 2007, an instrumented aircraft measured ice crystal size distributions, ice and liquid water contents, and atmospheric state parameters within a broad shield of precipitation generated by a passing midlatitude cyclone. The 94-GHz CloudSat radar acquired vertical profiles of radar reflectivity within light to moderate snowfall, coincident with C3VP surface and aircraft instrumentation. Satellite-based retrievals of cold season precipitation require relationships between remotely sensed quantities, such as radar reflectivity or brightness temperature, and the ice water content present within the sampled profile. In this study, three methods for simulating CloudSat radar reflectivity are investigated by comparing Mie spheres, single dendrites, and fractal aggregates represented within scattering databases or parameterizations. It is demonstrated that calculations of radar backscatter from nonspherical crystal shapes are required to represent the vertical trend in CloudSat radar reflectivity for this particular event, as Mie resonance effects reduce the radar backscatter from precipitation-sized particles larger than 1 mm. Remaining differences between reflectivity from nonspherical shapes and observations are attributed to uncertainty in the mass--diameter relationships for observed crystals and disparities between naturally occurring crystals and shapes assumed in the development of ice crystal scattering databases and parameterizations. [ABSTRACT FROM AUTHOR]

A bistatic lidar configuration of a wide-angle camera (100°°) and vertically pointed laser (532 nm) was used to profile aerosols at a coastal site. Aerosol profiles were measured on two evenings from the surface through the boundary layer. The site, on the eastern tip of the Big Island of Hawaii, is influenced by both marine boundary layer aerosols and breaking waves. Two nephelometers, located at 7 and 25 m above sea level, were compared directly with the 0.5-m-altitude resolution of the camera lidar (clidar). At 7 m, changes in aerosol were tracked quite well by the clidar. At 25 m the aerosol was fairly constant and a useful comparison could only be made with averaged values. The clidar results showed a steep gradient (decreasing with altitude) in the aerosol extinction from 7 to about 35 m. The gradient continued to 200 m at a lower rate. This demonstrated the use of the clidar in characterizing the environment for the in situ aerosol sampling. Both a measured and a NASA Aerosol Robotic Network (AERONET)-derived aerosol phase function, representing similar marine conditions but from different locations, were used to convert the single-angle clidar scatter to extinction. The measured function gave the best fit to the near-surface nephelometer data. The extinction/backscatter ratio, derived by comparing the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth to the integrated clidar profile, was higher than the long-term average value from the AERONET aerosol phase function. [ABSTRACT FROM AUTHOR]

Atmospheric boundary layer (ABL) observations were conducted in an urban area (Sapporo, Japan) from April 2005 to July 2007 using a three-dimensional scanning coherent Doppler lidar. During this period, 50 dust devil--like vortices were detected in the area; they occurred during the daytime and were located at vertices or in the branches of convective cells (''fishnet'' patterns of wind field). The diameters of the vortex cores ranged from 30 to 120 m, and maximum vorticity ranged from 0.15 to 0.26 s−−1. More than 60%% of the vortices were cyclonic; the rest were anticyclonic. The tangential velocity component of the strongest vortex varied from −−5.4 to ++1.4 m s−−1, and the signal-to-noise ratio was weak in the core. Temporal changes were observed in the three-dimensional structures of two vortices from 1330 to 1354 (Japan standard time) 14 April 2005, and the temporal evolution of the stronger vortex was studied. The vortex initially formed along a low-level convergence line in a fishnet and developed vertically. Its vorticity increased with time in association with shrinkage in the core diameter. [ABSTRACT FROM AUTHOR]

A second-generation diode-laser-based master oscillator power amplifier (MOPA) configured micropulse differential absorption lidar (DIAL) instrument for profiling of lower-tropospheric water vapor is presented. The DIAL transmitter is based on a continuous wave (cw) external cavity diode laser (ECDL) master oscillator that is used to injection seed two cascaded tapered semiconductor optical power amplifiers, which deliver up to 2- μμJ pulse energies over a 1- μμs pulse duration at 830 nm with an average power of ∼∼40 mW at a pulse repetition frequency of 20 kHz. The DIAL receiver utilizes a commercial 28-cm-diameter Schmidt--Cassegrain telescope, a 250-pm narrowband optical filter, and a fiber-coupled single-photon-counting Avalanche photodiode (APD) detector, yielding a far-field full-angle field of view of 170 μμrad. A detailed description of the second-generation Montana State University (MSU) DIAL instrument is presented. Water vapor number density profiles and time--height cross sections collected with the water vapor DIAL instrument are also presented and compared with collocated radiosonde measurements, demonstrating the instruments ability to measure night- and daytime water vapor profiles in the lower troposphere. [ABSTRACT FROM AUTHOR]

Following the discovery of anomalously high values of lidar integrated attenuated backscatter near the top center layers of mesoscale convective systems (MCSs) observed by the NASA Lidar In-Space Technology Experiment (LITE), a search of Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) data on board the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observation ( CALIPSO) platform revealed the same phenomena in a sample of eight MCSs investigated. The backscatter depolarization ratio also showed changes concurrent with the high integrated backscatter and either increased or decreased concurrently with the anomalous backscatter. Simultaneous CloudSat data in the A-Train formation showed a cloud-top altitude similar to that measured by CALIOP, indicating fairly large ice crystals were reaching cloud top. Based on previous work, the CALIOP and CloudSat returns were likely due to a mix of small ice droxtals or frozen drops extending in a continuous spectrum to large crystals composed of well-formed hexagonal columns, thick hexagonal plates, spheroids, and irregular particles. The CALIOP lidar would detect the whole spectrum whereas CloudSat would detect ice crystals greater than ∼∼30 μμm in effective radius; there were apparently enough of such crystals to allow CloudSat to detect a cloud-top height similar to that found by CALIOP. Using such a model, it was estimated that the measured backscatter phase function in the most active part of the cloud could be reconciled approximately with theoretical values of the various crystal habits. However, it was harder to reconcile the changes in depolarization ratio given the absence of values of this parameter for small droxtal crystals. [ABSTRACT FROM AUTHOR]

The accurate real-time detection of turbulent airflow patterns near airports is important for safety and comfort in commercial aviation. In this paper, a method is developed to identify Lagrangian coherent structures (LCS) from horizontal lidar scans at Hong Kong International Airport (HKIA) in China. LCS are distinguished frame-independent material structures that create localized attraction, repulsion, or high shear of nearby trajectories in the flow. As such, they are the fundamental structures behind airflow patterns such as updrafts, downdrafts, and wind shear. Based on a recently developed finite-domain--finite-time Lyapunov exponent (FDFTLE) algorithm from Tang et al. and on new Lagrangian diagnostics presented in this paper that are pertinent to the extracted FDFTLE ridges, the authors differentiate LCS extracted from lidar data. It is found that these LCS derived from horizontal lidar scans compare well to convergence and divergence suggested by vertical slice scans. At HKIA, horizontal scans are predominant: they cover much bigger azimuthal ranges as compared with only two azimuthal angles from the vertical scans. LCS extracted from horizontal scans are thus advantageous in providing organizing turbulence structures over the entire observational domain as compared with a single line along the vertical scan direction. In Part II of this study, the authors will analyze the evolution of LCS and their impacts on landing aircraft based on recorded flight data. [ABSTRACT FROM AUTHOR]