Search

[1] The daytime evolution of warm cloud microphysical properties over the southeast Pacific during October–November 2008 is investigated with optical/infrared retrievals from the Tenth Geostationary Operational Environmental Satellite (GOES-10) imager. GOES-10 retrievals, produced at NASA Langley Research Center, are validated against in situ aircraft observations and with independent satellite observations. Comparisons with in situ observations reveal high linear correlations (r) for cloud effective radius (re) and optical thickness (τ) (r = 0.89 and 0.69 respectively); nevertheless, a GOES-10 positive mean re bias of 2.3 μm is apparent, and consistent with other previously reported satellite biases. Smaller biases are found for liquid water path (LWP) and an adiabatic-based cloud droplet number concentration (Nd), both variables derived by combining re and τ.In addition, GOES-10 observations are well correlated with their Moderate Resolution Imaging Spectroradiometer (MODIS) counterparts, but with smaller biases and root-mean-square errors for the Aqua satellite passes, arguably associated with a better calibrated MODIS-Aqua instrument relative to MODIS-Terra. Furthermore, the excellent agreement between GOES-10 LWP and microwave-based satellite retrievals, especially at high solar zenith angles (>60°), provide further evidence of the utility of using GOES-10 retrievals to represent the daytime cloud cycle. In terms of the daytime cycle, GOES-10 observations show an afternoon minimum in LWP and an increase thereafter, consistent with satellite microwave climatologies. Theτ cycle explains most of the LWP variance with both variables in phase, minima near noon along the coast, and a 13:30–14:00 local solar time (LST) minimum offshore. In contrast, re is not exactly in phase with LWP and τ, having a minimum approximately at 12:30 LST throughout the domain. A unique feature is a striking re maximum along the coast at 16:15 LST, concomitant with a faster τ recovery. An explanation for a coastal reafternoon maximum is lacking although this is consistent with an enhancement of the updraft velocity reported in previous modeling studies. Finally, the GOES-derived Nd (Nd ∝ τ1/2 re−5/2) shows a complex daytime cycle with maxima at 7:15 and 13:15 LST. While the first maximum is driven by large τ, the second one is mainly explained by a minimum in re.

[1] A method for estimating effective ice particle radius Re at the tops of tropical deep convective clouds (DCC) is developed on the basis of precomputed look-up tables (LUTs) of brightness temperature differences (BTDs) between the 3.7 and 11.0 μm bands. A combination of discrete ordinates radiative transfer and correlated k distribution programs, which account for the multiple scattering and monochromatic molecular absorption in the atmosphere, is utilized to compute the LUTs as functions of solar zenith angle, satellite zenith angle, relative azimuth angle, Re, cloud top temperature (CTT), and cloud visible optical thickness τ. The LUT-estimated DCC Re agrees well with the cloud retrievals of the Moderate Resolution Imaging Spectroradiometer (MODIS) for the NASA Clouds and Earth's Radiant Energy System with a correlation coefficient of 0.988 and differences of less than 10%. The LUTs are applied to 1 year of measurements taken from MODIS aboard Aqua in 2007 to estimate DCC Re and are compared to a similar quantity from CloudSat over the region bounded by 140°E, 180°E, 0°N, and 20°N in the Western Pacific Warm Pool. The estimated DCC Re values are mainly concentrated in the range of 25–45 μm and decrease with CTT. Matching the LUT-estimated Re with ice cloud Re retrieved by CloudSat, it is found that the ice cloud τ values from DCC top to the vertical location where LUT-estimated Re is located at the CloudSat-retrieved Re profile are mostly less than 2.5 with a mean value of about 1.3. Changes in the DCC τ can result in differences of less than 10% for Re estimated from LUTs. The LUTs of 0.65 μm bidirectional reflectance distribution function (BRDF) are built as functions of viewing geometry and column amount of ozone above upper troposphere. The 0.65 μm BRDF can eliminate some noncore portions of the DCCs detected using only 11 μm brightness temperature thresholds, which result in a mean difference of only 0.6 μm for DCC Re estimated from BTD LUTs.

The spatial and temporal variability of nearshore winds in eastern boundary current systems affect the oceanic heat balance that drives sea surface temperature changes. In this study, regional atmospheric and oceanic simulations are used to document such processes during an atmospheric coastal jet event off central Chile. The event is well reproduced by the atmospheric model and is associated with the migration of an anomalous anticyclone in the southeastern Pacific region during October 2000. A robust feature of the simulation is a sharp coastal wind dropoff, which is insensitive to model resolution. As expected, the simulated oceanic response is a significant sea surface cooling. A surface heat budget analysis shows that vertical mixing is a major contributor to the cooling tendency both in the jet core area and in the nearshore zone where the magnitude of this term is comparable to the magnitude of vertical advection. Sensitivity experiments show that the oceanic response in the coastal area is sensitive to wind dropoff representation. This is because total upwelling, i.e., the sum of coastal upwelling and Ekman pumping, depends on the scale of wind dropoff. Because the latter is much larger than the upwelling scale, coastal wind dropoff has only a weak positive effect on vertical velocities driven by Ekman pumping but has a strong negative effect on coastal upwelling. Interestingly though, the weakening of coastal winds in the dropoff zone has a larger effect on vertical mixing than on vertical advection, with both effects contributing to a reduction of cooling.

[1] Dusty cloud properties and radiative forcing over northwestern China (source region) are compared to the same quantities over the northwestern Pacific (downwind region) during the Pacific Dust Experiment (PACDEX; April 2007 to May 2007) using collocated data from three satellites in the A-Train constellation: CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations), the Clouds and Earth Radiant Energy System on Aqua, and CloudSat. Dusty clouds are defined as clouds extant in a dust plume environment (i.e., dust aerosols observed within 50 m of the cloud), while pure clouds are those in dust-free conditions. CALIPSO lidar and CloudSat radar measurements are used to discriminate between dusty and pure clouds in both study regions. It was found that dust aerosols change the microphysical characteristics of clouds, reducing the cloud optical depth, liquid and ice water path, and effective droplet size. The decreased cloud optical depths and water paths diminish the cloud cooling effect, leading to a greater warming effect. The dust aerosols cause an instantaneous net cloud cooling effect of 43.4% and 16.7% in the source and downwind regions, respectively. The dust aerosol effects appear to be greater for ice clouds than for liquid water clouds in the downwind region. These results are consistent with PACDEX aircraft observations.

One of the main goals of the Tropical Composition, Cloud and Climate Coupling Experiment (TC(sup 4)) during July and August 2007 was to gain a better understanding of the formation and life cycle of cirrus clouds in the upper troposphere and lower stratosphere and how their presence affects the exchange of water vapor between these layers. Additionally, it is important to compare in situ measurements taken by aircraft instruments with products derived from satellite observations and find a meaningful way to interpret the results. In this study, cloud properties derived using radiance measurements from the Geostationary Operational Environmental Satellite (GOES) imagers are compared to similar quantities from aircraft in situ observations and are examined for meaningful relationships. A new method using dual \angle satellite measurements is used to derive the ice water content (IWC) for the top portion of deep convective clouds and anvils. The results show the in situ and remotely sensed mean microphysical properties agree to within approx.10 microns in the top few kilometers of thick anvils despite the vastly different temporal and spatial resolutions of the aircraft and satellite instruments. Mean particle size and IWC are shown to increase with decreasing altitude in the top few kilometers of the cloud. Given these relationships, it may be possible to derive parameterizations for effective particle size and IWC as a function of altitude from satellite observations

Upper troposphere cloud top heights (CTHs), restricted to cloud top pressures (CTPs) less than 500 hPa, inferred using four satellite retrieval methods applied to Twelfth Geostationary Operational Environmental Satellite (GOES-12) data are evaluated using measurements during the July August 2007 Tropical Composition, Cloud and Climate Coupling Experiment (TC4). The four methods are the single-layer CO2-absorption technique (SCO2AT), a modified CO2-absorption technique (MCO2AT) developed for improving both single-layered and multilayered cloud retrievals, a standard version of the Visible Infrared Solar-infrared Split-window Technique (old VISST), and a new version of VISST (new VISST) recently developed to improve cloud property retrievals. They are evaluated by comparing with ER-2 aircraft-based Cloud Physics Lidar (CPL) data taken during 9 days having extensive upper troposphere cirrus, anvil, and convective clouds. Compared to the 89% coverage by upper tropospheric clouds detected by the CPL, the SCO2AT, MCO2AT, old VISST, and new VISST retrieved CTPs less than 500 hPa in 76, 76, 69, and 74% of the matched pixels, respectively. Most of the differences are due to subvisible and optically thin cirrus clouds occurring near the tropopause that were detected only by the CPL. The mean upper tropospheric CTHs for the 9 days are 14.2 (+/- 2.1) km from the CPL and 10.7 (+/- 2.1), 12.1 (+/- 1.6), 9.7 (+/- 2.9), and 11.4 (+/- 2.8) km from the SCO2AT, MCO2AT, old VISST, and new VISST, respectively. Compared to the CPL, the MCO2AT CTHs had the smallest mean biases for semitransparent high clouds in both single-layered and multilayered situations whereas the new VISST CTHs had the smallest mean biases when upper clouds were opaque and optically thick. The biases for all techniques increased with increasing numbers of cloud layers. The transparency of the upper layer clouds tends to increase with the numbers of cloud layers.

Knowledge of long-range transport and vertical distribution of Asian dust aerosols in the free troposphere is important for estimating their impact on climate. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), surface micropulse lidar (MPL), and standard surface measurements are used to directly observe the long-range transport and vertical distribution of Asian dust aerosols in the free troposphere during the Pacific Dust Experiment (PACDEX). The MPL measurements were made at the Loess Plateau (35.95 degrees N, 104.1 degrees E) near the major dust source regions of the Taklamakan and Gobi deserts. Dust events are more frequent in the Taklamakan, where floating dust dominates, while more intensive, less frequent dust storms are more common in the Gobi region. The vertical distribution of the CALIPSO backscattering/depolarization ratios indicate that nonspherically shaped dust aerosols floated from near the ground to an altitude of approximately 9 km around the source regions. This suggests the possible long-range transport of entrained dust aerosols via upper tropospheric westerly jets. A very distinct large depolarization layer was also identified between 8 and 10 km over eastern China and the western Pacific Ocean corresponding to dust aerosols transported from the Taklamakan and Gobi areas, as confirmed by back trajectory analyses. The combination of these dust sources results in a two-layer or multilayered dust structure over eastern China and the western Pacific Ocean.

A multilayered cloud retrieval system (MCRS) is updated and used to estimate ice water path in maritime ice-over-water clouds using Visible and Infrared Scanner (VIRS) and Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) measurements acquired over the Tropics between January and August 1998. Lookup tables of top-of-atmosphere 0.65-mu m reflectance are developed for ice-over-water cloud systems using radiative transfer calculations for various combinations of ice-over-water cloud layers. The liquid and ice water paths, LWP and IWP, respectively, are determined with the MCRS using these lookup tables with a combination of microwave ( MW), visible ( VIS), and infrared (IR) data. LWP, determined directly from the TMI MW data, is used to define the lower-level cloud properties to select the proper lookup table. The properties of the upper-level ice clouds, such as optical depth and effective size, are then derived using the Visible-Infrared Solar-infrared Split-Window technique (VISST), which matches the VIRS IR, 3.9 mu m, and VIS data to the multilayer cloud lookup table reflectances and a set of emittance parameterizations. Initial comparisons with surface-based radar retrievals suggest that this enhanced MCRS can significantly improve the accuracy and decrease the IWP in overlapped clouds by 42 and 13% compared to using the single-layer VISST and an earlier simplified MW-VIS-IR (MVI) differencing method, respectively, for ice-over-water cloud systems. The tropical distribution of ice-over-water clouds is the same as derived earlier from combined TMI and VIRS data, but the new values of IWP and optical depth are slightly larger than the older MVI values and exceed those of single-layered clouds by 7 and 11%, respectively. The mean IWP from the MCRS is 8-14% greater than that retrieved from radar retrievals of overlapped clouds over two surface sites, and the standard deviations of the differences are similar to those for single-layered clouds. Examples of a method for applying the MCRS over land without MW data yield similar differences with the surface retrievals. By combining the MCRS with other techniques that focus primarily on optically thin cirrus over low water clouds, it will be possible to more fully assess the IWP in all conditions over ocean except for precipitating systems.