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Gravity wave packets excited by a source of finite duration and size possess a broad frequency and wave number spectrum and thus span a range of temporal and spatial scales. Observing at a single location relatively close to the source, the wave components with higher frequency and larger vertical wavelength dominate at earlier times and at higher altitudes, while the lower frequency components, with shorter vertical wavelength, dominate during the latter part of the propagation. Utilizing observations from the Na lidar at Utah State University and the nearby Mesospheric Temperature Mapper at Bear Lake Observatory (41.9°N, 111.4°W), we investigate a unique case of vertical dispersion for a spectrally broad gravity wave packet in the mesopause region over Logan, Utah (41.7°N, 111.8°W), that occurred on 2 September 2011, to study the waves' evolution as it propagates upward. The lidar-observed temperature perturbation was dominated by close to a 1 h modulation at 100 km during the early hours but gradually evolved into a 1.5 h modulation during the second half of the night. The vertical wavelength also decreased simultaneously, while the vertical group and phase velocities of the packet apparently slowed, as it was approaching a critical level during the second half of the night. A two-dimensional numerical model is used to simulate the observed gravity wave processes, finding that the location of the lidar relative to the source can strongly influence which portion of the spectrum can be observed at a particular location relative to a source.

While the mesospheric temperature anomalies associated with Sudden Stratospheric Warmings (SSWs) have been observed extensively in the polar regions, observations of these anomalies at midlatitudes are much more sparse. The Rayleigh-scatter lidar system, which operated at the Center for Atmospheric and Space Sciences on the campus of Utah State University (41.7°N, 111.8°W), collected a very dense set of observations, from 1993 to 2004, over a 45–90 km altitude range. This paper focuses on Rayleigh lidar temperatures derived during the six major SSW events that occurred during the 11 year period when the lidar was operating and aims to characterize the local response to these midlatitude SSW events. In order to determine the characteristics of these mesospheric temperature anomalies, comparisons were made between the temperatures from individual nights during a SSW event and a climatological temperature profile. An overall disturbance pattern was observed in the mesospheric temperatures associated with SSW events, including coolings in the upper mesosphere and warmings in the upper stratosphere and lower mesosphere, both comparable to those seen at polar latitudes.

Rayleigh-scatter lidar observations were made at the Atmospheric Lidar Observatory (ALO) at Utah State University (USU) from 1993–2004 from 45–90 km. The lidar operated at 532 nm with a power-aperture-product (PAP) of ~3.1 Wm2. The sensitivity of the lidar has since been increased by a factor of 66 to 205 Wm2, extending the maximum altitude into new territory, the lower thermosphere. Observations have been extended up to 115 km, almost to the 120 km goal. Early temperatures from four ~4-week periods starting in June 2014 are presented and discussed. They are compared to each other, to the ALO climatol Conference paper accompanying poster submitted to the 27th International Laser Radar Conference, New York, NY, July 5-10, 2015 ogy from the original lidar [1], and to temperatures from the NRLMSISe00 empirical model [2].

We present an unprecedented comparison of temperature measurements from the Rayleigh-scatter (RS) and sodium (Na) lidar techniques. The extension of the RS technique into the lower thermosphere that has been achieved by the group at Utah State University (USU), enables simultaneous, common-volume measurements by the two lidar systems hosted in the Atmospheric Lidar Observatory at USU. The two lidars’ nightly averaged temperatures from 80-105 km, based on 19 nights of observations, are explored.

The TA observatory is a hybrid detector system consisting of both a surface detector array as well as a set of fluorescence detectors. The observatory will measure the energy spectrum, anisotropy and composition of ultra-high energy cosmic rays. The surface detectors are being deployed and the array should be complete by the end of February, 2007. We will soon be collecting hybrid data at the Telecope Array.

While mesospheric temperature anomalies associated with Sudden Stratospheric Warmings (SSWs) have been observed extensively in the polar regions, observations of these anomalies at midlatitudes are sparse. The original Rayleigh-scatter lidar that operated at the Atmospheric Lidar Observatory (ALO; 41.7°N, 111.8°W) in the Center for Atmospheric and Space Sciences (CASS) on the campus of Utah State University (USU) collected an extensive set of temperature data for 11 years in the 45–90 km altitude range. This work focuses on the extensive Rayleigh lidar observations made during six major SSW events that occurred between 1993 and 2004, providing a climatological study of the midlatitude mesospheric temperatures during these SSW events. An overall disturbance pattern was observed in the mesospheric temperatures during these SSWs. It included coolings in the upper mesosphere, comparable to those seen in the polar regions during SSW events, and warmings in the lower mesosphere.

A method has been developed for the retrieval of mesospheric temperatures in the 65–90 km altitude range from satellite observations made by the Wind Imaging Interferometer (WINDII) aboard the Upper Atmosphere Research Satellite (UARS). Retrieved temperatures are derived from Rayleigh scattered sunlight observed in a wavelength band centered at 553 nm. Integrated line-of-sight radiance observations are inverted to tangent height volume scattering profiles, which are proportional to atmospheric density. From these, absolute temperature profiles are calculated using a technique derived from established Rayleigh lidar retrieval methods assuming that the atmosphere is in hydrostatic equilibrium and that it obeys the ideal gas law. Sources of error have been identified and typical temperature uncertainty values for individual profiles are determined to be < 2.5%, 5.5%, and 13% for altitudes of 70 km, 80 km, and 90 km, respectively. A thorough comparison of the derived WINDII temperatures is performed against a number of ground-based and satellite measurements, including ground-based lidar, falling spheres, the High Resolution Doppler Imager observations aboard UARS, and against common atmospheric models. The data consist of spring equinox observations in March and April 1992/1993, summer solstice data in July/August 1992/1993, fall equinox data in September/October 1992, and winter solstice data in December 1992/1993 and January 1993/1994. The results of the comparisons show that WINDII temperatures are in reasonable to excellent agreement with a number of established temperature studies. In particular, July Northern Hemisphere monthly averaged temperatures show that characteristics of the mesopause obtained by WINDII are in very good agreement with other measurements. This good agreement with other established data sets and a determination of the error bounds of our recovered temperatures have shown that WINDII data can be used to confidently derive near-global temperatures of the upper mesosphere between 65 and 90 km. Above 90 km the errors increase, and systematic differences may arise with other measurements.

Having ionospheric electron density distributions as a function of height, latitude, longitude, and time under different conditions is essential for scientific, technical, and operational purposes. A satellite-based, swept-frequency, HF sounder can obtain electron density profiles on a global scale. We are developing a new generation HF sounder that employs recent developments in technology, electronics, and processing capabilities. It will provide global-scale electron density distributions, contours of fixed densities, maps of ƒoF2, hmax, etc. It will allow us to map irregularities, estimate anomalous propagation and conditions for ducting, determine angles of arrival, etc. It will also be able to perform various plasma diagnostics and, because of new flexibility, will be programmable from the ground to perform a variety of experiments in space. Need for such a system exists through the Department of Defense and several civilian agencies. Some of the novel features of the system include software-based design, direction of arrival estimation and synthetic aperture radar-type operation, onboard processing, and reconfigurable and flexible architecture with multimission capabilities.

The ionosphere, embedded in and tightly coupled to the thermosphere, is strongly influenced by couplings to other geophysical regions. For example, above it, both the magnetosphere and plasmasphere greatly affect the ionosphere by the precipitation of soft and energetic particles, by heat conduction, and by fluxes of thermal particles. Below, the middle atmosphere affects it with upwardly propagating waves (gravity waves, tides, and planetary waves). All the while, polar and auroral regions greatly affect the mid-latitudes by the equatorward penetration of electric fields and winds, and by the equatorward propagation of waves (traveling ionospheric disturbances or TIDs). Exploring these couplings effectively furthers our understanding of at least the dominant processes and interactions that play such an important role in determining the character of this part of the Earths environment. Significant progress during the Solar-Terrestrial Energy Program (STEP) has demanded that the observational, analytical, and theoretical thrusts of the international scientific community be global in all senses. Observationally, this has led to coordinated measurements from many regions, from the poles to the equator, and from ground- and space-based instruments. It has also led to many different instruments, including new ones, measuring an extensive variety of (related) geophysical parameters. Depending on the instrument, measurements have been made continuously or at appropriate intervals to sample different geomagnetic conditions, and diurnal, seasonal, inter-annual, and solar-cycle variations. Extensive analyses have been carried out on these observations. New empirical models have been developed and old ones improved. Theoretical work has led to new and improved first-principles models that are being used to test our understanding of the observations. Our intent is to review this progress and suggest some future directions. Our approach is to illustrate the broad front of progress with representative examples, rather than to do an exhaustive review. We apologize from the start, to those whose good work we have not noted, in order to allow a broad balanced overview of areas advanced.

The flux-corrected transport (FCT) technique and the alternating-direction explicit (ADE) method are coupled through a time-splitting technique. This new combination of both methods has been used successfully to solve the fully coupled Navier?Stokes system applied to ionospheric thermal plasma flows with a viscosity and strong heat conduction. The combined scheme gives convergent solutions within the time step set for nonlinear stability of the corresponding nondissipative flow fields, and the time-dependent solutions are consistent with other model results using different methods. To have a quantitative view of the flux-limiter of Boris' FCT version, a concept of local variation is defined to identify local extrema. The total variation diminishing scheme finds unique entropy solutions for vanishing dissipation. The ADE scheme, however, enables us to handle dissipation when the FCT technique alone can be inappropriate.

Rayleigh lidar observations of mesosphere temperature profiles obtained from 40 to ∼100 km from Logan, Utah (41.7, 111.8 W, altitude, 1.9 km) over 10 nights in late February, 1995, revealed an interesting development between 60 to 75 km of a winter mesosphere inversion layer with an amplitude of ∼20–30 K and a downward phase progression of ∼1 km/hr. The data also showed two altitude regions exhibiting significant cooling of 10–30 K in extent. These were located below and above the peak of the inversion layer, respectively, at altitudes of ∼50–55 km and ∼70–80 km. When these results were compared with the predictions of a global wave scale model (GSWM), the observed thermal mesosphere structure is similar to the computed composite tidal structure based upon the semi-diurnal and diurnal tides with the exception that observed amplitudes of heating and cooling are ∼10x larger than predicted GSWM values. We suggest that these events over Utah are caused through a localized mechanism involving the coupling of gravity waves to the mesopause tidal structure.

Doppler temperatures have been obtained in the mesopause region (∼85 km) above Bear Lake Observatory, Utah, over a period of two years, using the hydroxyl (OH) emission. The mid-latitude mesopause temperature decreases ∼60 K from a winter maximum of ∼220 K to a summer minimum of ∼160 K. ‘Sudden Mesopause Cooling’ Events of ∼30 K amplitude have been observed during mid-winter, one in January 1994 and two in January / February 1995, which appear to be associated with ‘stratospheric sudden warming’ phenomena. Tidal variations in temperature can be observed by taking hourly averages of data over a one-month period. The largest tidal amplitudes, of ∼10 – 20 K, occur during winter, while amplitudes in summer are smaller, ∼2 K.

Very accurate measurements of electron density can be made at Arecibo Observatory, Puerto Rico, by applying the coded long-pulse (CLP) radar technique [Sulzer, 1986a] to plasma line echoes from daytime photoelectrons [Djuth et al., 1994]. In the lower thermosphere above Arecibo, background neutral waves couple to the ionospheric plasma, typically yielding ∼1–3% electron density “imprints” of the waves. These imprints are present in all observations made to date; they are decisively detected at 30–60 standard deviations above the “noise level” imposed by the measurement technique. Complementary analysis and modeling efforts provide strong evidence that these fluctuations are caused by internal gravity waves. Properties of the neutral waves such as their period and vertical wavelength are closely mirrored by the electron density fluctuations. Frequency spectra of the fluctuations exhibit a high-frequency cutoff consistent with calculated values of the Brunt-Vaisala frequency. Vertical half wavelengths are typically in the range 2–25 km between 115- and 160-km altitude, and the corresponding phase velocities are always directed downward. Some waves have vertical wavelengths short enough to be quenched by kinematic viscosity. In general, the observed electron density imprints are relatively “clean” in that their vertical wavelength spectrum is characteristically narrow-banded. It is estimated that perturbations in the horizontal wind field as small as 2–4 m/s can give rise to the observed electron density fluctuations. However, the required wind speed can be significantly greater depending on the orientation of the neutral wave's horizontal wave vector relative to the geomagnetic field. Limited observations with extended altitude coverage indicate that wave imprints can be detected at thermospheric heights as high as 500 km.

The Imaging Fabry-Perot Interferometer (IFPI) at the Bear Lake Observatory (BLO), Utah (41.9°N, 111.4°W) is used for studies of the aeronomy of the middle and upper atmosphere. Wind and temperature structure can be determined from observations of the Doppler shift and Doppler broadening of the airglow and auroral emissions from the mesosphere and thermosphere. The mesospheric winds recorded at the end of August, September and early October 1992 are consistent with a semi-diurnal tidal variation. The amplitude of this variation is approximately 30 ms−1 at the end of August and early September and approximately 20 ms−1 at the end of September and early October. However, during June and July, the semi-diurnal tidal variation, if present, is weak, with amplitude < 5 ms−1. No consistent semi-diurnal tidal variation is observed during late October 1992. During the solstice period, antisymmetric tidal components may be preferentially generated in such a way that they can result in destructive interference with the normally dominant symmetric modes, resulting in a decrease of tidal variation. This is consistent with the observed decrease in tides during the June, July and late October periods. Near the equinoxes, however, the excitation of these antisymmetric modes is expected to be weaker, possibly explaining why a pronounced and consistent semi-diurnal tidal variation has been observed during the August, September and early October periods. In contrast, the mesospheric winds derived from the Sheffield Meteor Wind Radar (53.4°N, 1.5°W) reveal a clear semi-diurnal tidal variation throughout the year, with an amplitude that may vary between 15 ms−1 and 50 ms−1, being about 25 ms−1 on average. The IFPI records winds from a region of the atmosphere centred at 87 km, whereas the Sheffield Meteor Wind Radar measures winds centred at 95 km. Therefore, the two regions may experience different tidal modes due to the different latitude, longitude and altitude of the observed regions and/or the different topography of the observing sites. Some proposed reasons for these differences are presented.

A Rayleigh lidar was operated from 1993 to 2004, at the Atmospheric Lidar Observatory (ALO; 41.7°N, 111.8°W) at the Center for Atmospheric and Space Sciences (CASS) on the campus of Utah State University (USU). Observations were carried out on over 900 nights, 729 of which had good data starting at 45 km and going upward toward 90 km. They were reduced for absolute temperatures and relative neutral number densities. The latter at 45 km can be put on an absolute basis by using atmospheric models that go up to at least 45 km. The models’ absolute number densities at 45 km are used to normalize the lidar observations, thereby providing absolute densities from 45 to 90 km. We examine these absolute density profiles for differences from the overall mean density profile to show altitudinal structure and seasonal variations.

t is no longer sufficient to use lidar, such as the Rayleigh lidar at the Atmospheric Lidar Observatory (ALO) at Utah State University (USU), to observe the middle atmosphere and reduce the data to geophysical parameters. Extended operations, with inevitable equipment, data reduction, and analysis improvements, require us to keep careful track of all these changes and how they affect the scientific products. Furthermore, many of the funding agencies and the journals now require us to do, at least, some of this. We have built three interconnected data structures to organize and manage the different hardware and software set- ups from the Internet as well as to keep track of the products generated by these. These structures were implemented as a database, which is particularly important for groups with a large volume of information like the Rayleigh Group at ALO-USU.

The first stage of a new midlatitude facility at the Hardware Ranch Observatory near Bear Lake (41.93°N, 111.42°W, 1970 M elevation), for studies of the aeronomy of the middle and upper atmosphere, was completed during early September 1989. An Imaging Fabry‐Perot interferometer (IFPI) (Rees et al., 1982; Rees et al., 1990), was commissioned with a special Imaging Photon Detector (IPD) (McWhirter et al., 1982), equipped with a Gallium Arsenide (GaAs) photocathode. Wind and temperature structure can be deduced from observations of the Doppler shift and Doppler broadening of airglow and auroral emissions from the mesosphere and thermosphere. The near infra‐red Meinel bands from near 86 km in the upper mesosphere were observed with the IFPI and show 40 ms−1 amplitude wind oscillations, consistent with a semi‐diurnal tidal mode.

[1] A Rayleigh-scatter lidar has been operated at the Atmospheric Lidar Observatory (ALO) on the Utah State University (USU) campus (41.7°N, 111.8°W) since August 1993. During the morning of 22 June 1995, lidar returns from a noctilucent cloud (NLC) were observed for approximately 1 hr, well away from the twilight periods when NLCs are visible. This detection of an NLC at this latitude shows that the first reported sighting, in 1999 (Wickwar et al., 2002), was not a unique occurrence. This 1995 observation differs from the 1999 one in that temperatures could be deduced. Near the 83-km NLC altitude the temperatures were found to be up to ∼23 K cooler than the 11-year June climatology for ALO. This analysis shows that these cool temperatures arose, not because the whole profile was cooler, but because of a major temperature oscillation or wave with a 22-km vertical wavelength and a ∼0.9 km/hr downward phase speed. This large-amplitude wave has many of the characteristics of the diurnal tide. However, the amplitude would have to be enhanced considerably. These lidar observations were supplemented by OH rotational temperature observations from approximately 87 km. These NLC observations equatorward of 50° have been suggested to be significant harbingers of global change. However, if that were the case, the mechanism is more complicated than a simple overall cooling or an increase in water vapor. Accordingly, we propose enhanced generation of gravity waves that would interact with the diurnal tide to produce a large-amplitude wave, the cold phase of which would give rise to low enough temperatures to produce the NLC. The gravity wave source might be orographic in the Mountain West or convective far to the east or south.

Data obtained from the USU incoherent backscatter lidar at Logan Utah during the interval 1994 through 1998 has been analyzed in terms of the climatology of stratospheric and lower mesospheric mean density and density variance (delta) (rho) /(rho) )2 vs. altitude. The total database consists of over 322 nights of cloud-free data over the altitude range, 40 to 90 km. We selected a subset of 142 days (886 hours) of the highest signal to noise ratio data for the analysis. The temporal and spatial resolutions were 2 minutes and 112.5 meters respectively. We compared the mean density profiles, normalized to MSISe90 on a monthly and seasonal basis to MSISe90. The mean density profiles compared well with the MSISe90 model with the following exceptions. The measured densities were less than MSISe90 predictions in the 45 to 80 km range by up to 10% in the 1st calendar quarter, and greater than MSISe90 density predictions in the last calendar quarter, by about 8 to 10 %, but over a narrower altitude range. The density variance profiles (delta) (rho) /(rho) )2 are proportional to the mean free energy of the atmospheric gravity wave and turbulent structure.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have developed a pulsed, narrow line Raman shifted alexandrite laser to produce tunable near-IR radiation in the 1140 nm absorption band of water vapor. With the first Stokes Raman conversion in hydrogen, the full tuning range of alexandrite, 730-790 nm, can potentially cover the wavelength range 1050 1200 nm. The application to differential absorption lidar, DIAL, is the vertical profiling of humidity and temperature in the atmosphere. This paper reports the application of Raman-shifted alexandrite radiation for new quantitative measurements of the strengths and widths of water vapor absorption lines between 8865 and 8915 cm -1 . Alexandrite wavelength determination was obtained with oxygen A-band rotational lines near 765 nm. Similar applications and studies of the water vapor band near 940 nm can be readily carried out by Raman-shifting in deuterium.

[1] Noctilucent clouds (NLCs) were observed from a midlatitude site (Logan, Utah) on the evenings of 22 and 23 June 1999 mountain daylight time. On both nights the clouds were seen for approximately an hour by experienced observers, and they were photographed. The NLC was also observed on the second evening for approximately an hour in the zenith with the Rayleigh-scatter lidar at the Atmospheric Lidar Observatory, which is operated by the Center for Atmospheric and Space Sciences on the campus of Utah State University. These observations enabled several of the properties of the cloud to be determined. They were within the range of those observed at higher latitudes, but notably the NLC was very weak and thin. These combined visual and lidar observations unequivocally support the identification of the cloud as a noctilucent cloud. The midlatitude location (41.74°N, 111.81°W) is ∼10° equatorward of previous observations. This equatorward penetration is significant because of potential implications about global change or the global circulation.

The Center for Atmospheric and Space Sciences (CASS) at Utah State University (USU) operates the ALO for studying the middle atmosphere from the stratosphere to the lower thermosphere. ALO's mid-latitude location (41.74°N, 1 1 1.81°W, 1466 m) is very unique in that it is in the middle of an extensive set of rugged mountains, the Rocky Mountains, which are a major orographic source of gravity waves that may give rise to a longitudinal variation in the mesospheric structure. Mesospheric observations between approximately 45 and 90 km have been carried out on many clear nights with the ALO Rayleighscatter lidar since late 1993. They have been carried out, mostly, with a frequency-doubled Nd:YAG laser producing 18 W at 532 nm and a 44-cm zenith-pointing telescope. To obtain better and more complete observations in the future, a considerably bigger steerable telescope, an alexandrite ring laser for resonance scatter, and an expanded data-acquisition system are being developed. The observations in the extensive existing database have been reduced to provide absolute temperature profiles, which provide important information for understanding the physics and chemistry of the middle atmosphere and for examining global change. They have been used to make a mesospheric temperature climatology that has been and is being used to examine secular, annual, seasonal, and tidal variations, to compare with other temperature observations and with modeled temperatures, and to study mesospheric inversion layers. Day-to-day changes in the temperature profiles are also being compared to meteorological parameters to see if mesospheric changes can be related to low-altitude sources. Temporal and spatial fluctuations in the density profiles have also been examined to provide more direct information on gravity wave activity. And, on 24 June 1999 UT, the lidar probed the first known noctilucent cloud to penetrate to this low latitude, approximately 10° equatorward of previously reported sightings and detections.

Temporal and spatial spectral analysis techniques were applied to lidar data collected over a period of 18 months above the Rocky Mountain region at an altitude range from 45 to 70 km by a Rayleigh lidar system located in Logan, Utah (41.7°N, 111.8°W). Examination of the averaged temporal frequency F(ω) and vertical wavenumber F(m) spectra showed spectral slope values of −1.49 ± 0.03 and −2.3 ± 0.1, respectively. The observed slope for the overall averaged F(m) spectrum is considerably more positive than the value of −3 predicted by the linear instability theory but close to the value of ∼−2 that is predicted by the scale independent diffusive filtering theory using the measured F(ω) slope parameter. However, examination of the monthly averaged F(m) spectra for the transition from winter to summer showed the spectra became flatter suggesting that Doppler shift effects caused by the seasonal change in the magnitude and direction of the background wind field are significant. The characteristic vertical wavelength λ* was found to be ∼12 km for the altitude region of 45–70 km. Comparison of this value with the characteristic wavelengths from other lidar observations at lower and higher altitude ranges showed an overall increase of λ* with height. The observed enhancement of the F(m) spectral magnitude in winter is believed to be caused in part by the low–frequency wave activity observed in the temperature profiles.

The spatial and temporal distributions of density structure in the upper stratosphere and lower mesosphere (40 to 80 km altitude) are observed by Rayleigh scatter lidar at USU. We utilize advanced two dimensional Fourier filter techniques to derive estimates of the temporal and spatial (altitude) power spectral densities for the altitude-binned and time-binned structure, and of the 2-D space-time structure of an entire observing period (e.g., 8 hours). Coherent, wavelike spectra are observed in both altitude and time, and appear to be superimposed upon a background of continuous spectral power which may be characteristic of unsaturated turbulence. We observe upwardly propagating gravity waves having (downward) vertical phase velocities in the approximate range 0.15 to 1 meter/second (0.5 to 4 km/hr.). Wave structures are often not apparent in the raw density fluctuation data, but are brought out clearly by means of a 2-D Parzen filter in Fourier space followed by appropriate reconstruction of the density fluctuations in altitude-time coordinates.

The Atmospheric Lidar Observatory (ALO) at Utah State University has recently acquired an alexandrite laser, developed by Light Age Incorporated, that is a relatively new type of configuration, ideal for resonance lidar and DIAL observations. Unidirectional ring lasing is established in a two-rod cavity, producing single longitudinal and transverse mode (TEM00) pulses up to 200 mJ in energy and having a pulse length of 100 nsec or greater. This paper is, in part, a progress report on the advanced technology behind this new type of alexandrite laser, and how the new performance level will impact atmospheric lidar observations. We have not yet operated the USU alexandrite laser as a lidar transmitter, but have carried out the construction and testing of this and two other similar lasers, one of which is lidar-operational, and the other is currently being installed for the same purpose. This paper reviews some of the salient features of alexandrite as a laser medium, provides details on the current state-of-the-art of this tunable frequency-stabilized laser, and outlines the capabilities for geophysical lidar measurements using the alexandrite laser.

From Aug. 1993 to Feb. 1996, regular Rayleigh-scatter observations of the stratosphere and mesosphere in the altitude range 40–95 km were made with the Consortium Lidar (CL) located at Utah State University. These observations are now being continued with the Atmospheric Lidar Observatory (ALO) at the same location. The site is located at mid latitude in the middle of the Rocky Mountains—41.75° N, 111.80° W. Atmospheric density profiles derived from the lidar returns are reduced to temperature profiles, with considerable care being taken to avoid possible systematic errors. In summer months, the Utah mesospheric temperatures, like those from elsewhere, show the least variability and the expected monotonic decrease of temperature with altitude. However, the Utah temperatures appear systematically lower than others. Between spring and fall, an important feature of the temperature climatology is a strong asymmetry, which appears to be larger than elsewhere. In winter, day-to-day temperature variability is greatest, but variability also exists on the scale of a week. Perhaps as a consequence, or perhaps for another reason, the Utah data show an enormous change from one January to the next. Are these differences in the climatology real? If so, can they be related to the mountainous location and the orographic generation of gravity waves? Can the temporal variations be related to planetary (Rossby) waves and the generation of gravity waves by the jet stream?

Telescope Array (TA) is a hybrid detector of a surface detector array and fluorescence telescopes. This hybrid detector will measure the energy spectrum, anisotropy and composition of ultra-high energy cosmic rays (UHECRs) to identify their origin. The almost construction of the detector has been completed in May 2007, and the detector is running under test and adjustments. The first hybrid observation with the full configuration is planned in beginning of 2008. In this paper the status and prospects of TA detector is described.

We report on a wide variety of thermospheric and ionospheric observations from three consecutive January World Day campaign periods. Despite remarkably similar geophysical conditions characterizing the in situ forcing of the upper atmosphere during these solar minimum campaigns, we find significant variability in the observations of the ionosphere and thermosphere particularly at low latitudes in the American sector. In addition, we present further observational evidence of the unexpected exospheric temperature suppression at low latitudes initially reported by Hagan and Salah (1988). We discuss the lower and upper atmospheric coupling mechanisms of plausible importance to the interpretation of the observed thermospheric weather patterns. We report evidence that lower thermospheric [NO] (nitric oxide number density) and upward propagating atmospheric tides affected the thermospheric energy and momentum budgets during the campaign periods.

Thermospheric wind data obtained from the Atmosphere Explorer E and Dynamics Explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground-based incoherent scatter radar and Fabry-Perot optical interferometers to generate a revision (HWM90) of the HWM87 empirical model and extend its applicability to 100 km. Comparison of the various data sets with the aid of the model shows in general remarkable agreement, particularly at mid and low latitudes. The ground-based data allow modeling of seasonal/diurnal variations, which are most distinct at mid latitudes. While solar activity variations are now included, they are found to be small and not always very clearly delineated by the current data. They are most obvious at the higher latitudes. The model describes the transition from predominately diurnal variations in the upper thermosphere to semidiurnal variations in the lower thermosphere and a transition from summer to winter flow above 140 km to winter to summer flow below. Significant altitude gradients in the wind are found to extend to 300 km at some local times and pose complications for interpretation of Fabry-Perot observations.

Measurements of night-time 6300 A airglow intensities at the Arecibo Observatory have been compared with dissociative recombination calculations based on electron densities derived from simultaneous incoherent backscatter measurements. The agreement indicates that the nightglow can be fully accounted for by dissociative recombination. The comparisons are examined to determine the importance of quenching, heavy ions, ionization above the F-layer peak, and the temperature parameter of the model atmosphere. Comparable fits between the observed and calculated intensities are found for several available model atmospheres. The least-squares fitting process, used to make the comparisons, produces comparable fits over a wide range of combinations of neutral densities and of reaction constants. Yet, the fitting places constraints upon the possible combinations; these constraints indicate that the latest laboratory chemical constants and densities extrapolated to a base altitude are mutually consistent.

Dayside ionosphere convection at high latitudes has been examined during a series of experiments using the Sondrestrom radar together with ancillary observations of the interplanetary magnetic field (IMF) by the IMP-8 spacecraft. The radar experiments obtained a latitude coverage of 67.6 to 81.3 deg Lambda and a temporal resolution of between 14 to 25 minutes. A total of 17 rotations through the dayside cleft region during April, June and July, 1983 have been examined. The observations show two convection cells with sunward flow at lower latitudes and antisunward flow at higher latitudes. The flow commonly rotates through a 180 deg angle resulting in the predominant appearance of east-west flows. Rapid temporal variations in the convection velocities are frequently observed. Many of the high latitude variations in convection velocity appear to be directly related to variations in the IMF By component, with eastward (westward) velocity associated with negative (positive) By. This is strong evidence for a direct electrical coupling between the solar wind and dayside high latitude ionosphere.

Sondrestrom observations show that a characteristic F‐region signature of the interaction between the magnetosphere and ionosphere is a narrow band of elevated electron temperatures. Its location is associated with the ion convection reversal in the morning and evening convection cells. Typically, near 500 km altitude, the temperature is 3500 to 4000 K. However, on 24 April 1983, a geomagnetically very active day with Kp values of 6‐ during the period of interest, the electron temperature reached 6000 K in the afternoon convection reversal. The ion velocities were between 1 and 2 km/s on both sides of the reversal. There was considerable soft particle precipitation and a large downward heat flux of 0.3 erg/cm²‐s at 450 km. These high temperature electrons then transferred 0.5 erg/cm²‐s to ions and neutrals between 175 and 550 km, which represents a very sizeable perturbation to the thermosphere.

In this paper we describe the results of a series of geomagnetic meridian plane radar incoherent scatter plasma transport measurements. From such data the eastward (zonal) component of the electric field can be deduced. The results show that the electric field has an eastward component whenever the discrete auroras are northward of the region of the measurement. The zonal field component turns westward as the discrete auroras move equatorward of the region of the measurement. Thus there is an eastward electric field boundary near the equatorward limit of the discrete aurora, which is the poleward boundary of the diffuse aurora during undisturbed periods. During a particularly disturbed period we also observed three pronounced substorm-related enhancements of the westward-directed zonal field. For midnight and morning sector substorms the enhancements preceded the substorm onset times by 20–30 min. We show from meridian chain all-sky camera data that all three enhancements coincided with equatorward expansions of the auroral oval.

The ground-level zenith radiance of the atmospheric emission at λ 1.27 μm was radiometrically observed to increase by a factor of approximately two with the onset of an IBC III + auroral breakup above Chatanika, Alaska, on 10 March 1975. Time-resolved optical spectra clearly show that the slow component of the enhancement is associated with the (0,0) band of the infrared atmospheric system of O 2 . Photometric and incoherent scatter radar data are used to define the energy-deposition profile and the absolute energy flux for the event. The magnitude of the O 2 λ 1.27- μm enhancement compares favourably with the predictions of an auroral excitation model which includes only secondary-electron excitation of molecular oxygen in the O 2 ( a 1 Δ g ) source term.

First results are reported of a comprehensive campaign to measure ionospheric structure and dynamics of nighttime polar cap F‐layer or F‐region arcs. Airborne optical and digital ionosonde data were collected simultaneously with ground based incoherent scatter radar data, continuously over many hours in time and 500 to 1000 km in space. Polar cap F‐region sub‐visual auroral arcs, which are commonly observed during quiet magnetic conditions, are found to represent boundaries (or shears) in the polar cap plasma circulation pattern. F‐region electron concentration enhancements are found in these features and can be of significance to polar thermospheric circulation, composition, and thermal structure. The quiet polar ionosphere is so structured that high time resolution intensified optical images of thermospheric emmissions can make a major contribution to interpretation of incoherent scatter radar data.

By analyzing an observed storm time auroral electron temperature profile it is shown that anomalous transport effects strongly influence the thermal structure of the disturbed auroral ionosphere. Such anomalous transport effects are a consequence of plasma turbulence, the existence of which has been established by a large number of observations in the auroral ionosphere. The electron and composite ion energy equations are solved with anomalous electron thermal conductivity and parallel electrical resistivity coefficients. The solutions are parameterized with respect to a phenomenological altitude-dependent anomaly coefficient A and are compared with an observed storm time electron temperature profile above Chatanika. The calculated temperature profile for the classical case (A = 1) disagrees considerably with the measured profile over most of the altitude range up to 450 km. It is shown that an anomaly coefficient with a sharp peak of the order of 10,000 centered around the F2 peak is consistent with observations.

Observations of nighttime thermospheric neutral winds made at Sondre Stromfjord, Greenland, with optical and radar instrumentation, showed an occasional abatement in the equatorward meridional wind at a magnetic local time corresponding to the nighttime division between the evening and morning convection cells. This abatement appeared primarily in the poleward observations. In contrast, however, the characteristic midnight “surge” was usually seen in the equatorward set of observations. The apparent acceleration of about 250 m/s or greater within 4.6° latitude we attribute, in part, to a merging of neutral jet streams generated by polar cap ion drag adjacent to the auroral zone boundary, and, in part, to the higher electron densities and plasma convection speeds adjacent to the auroral zone. Comparison of these results with those from NCAR/TGCM computations that assumed an analytical plasma convection model showed reasonable agreement, except for the abatement feature.

Among the parameters we can deduce from incoherent-scatter radar measurements in the thermosphere is the meridional wind - the horizontal neutral wind in the magnetic north-south direction. Since this was first realized in 1967, radar observations have contributed greatly to the study of thermospheric dynamics. At mid and low latitudes, they have shown the important impact that tides propagating upward, from the lower atmosphere, have on the dynamics at F-region altitudes. At high latitudes, radar measurements have demonstrated what effects momentum and energy transfer from the magnetosphere have on the dynamics at F-region altitudes; including local ion drag, equatorward surge near midnight, IMF B y , local Joule heating, high-latitude heating, and midnight abatement and reversal. More generally the radar data have been used to confirm basic ideas about the global meridional circulation. Initially this was done with individual radars; now coordinated observations by a network of radars take data for periods of from one to five days. These global observations provide measurements of the full diurnal pattern at multiple locations as a function of season, magnetic activity, solar cycle, and of many other geophysical parameters. These multiday campaigns have contributed significantly to major ongoing programs such as CEDAR and WITS, and are planned to support future ones, such as STEP. The breadth of these programs is especially significant today. We are entering a new era when radar observations, combined with those from other instruments, can be used in conjunction with major theoretical models to test our quantitative understanding of the myriad physical processes and interactions that give rise to the winds and other geophysical parameters in the upper atmosphere.

A series of simultaneous incoherent-backscatter and 6300 A tilting-filter photometer observations were made in the winter and early spring of 1972 at Chatanika, Alaska. These observations have been combined for magnetically quiet nights to deduce the presence of excitation by two sources in addition to dissociative recombination. The first appears to be a source that is steady for at least three hours, centered about local midnight, but that varies from night to night, taking on values between 10 and 40 Rayleighs for the nights in question. It is suggested that this source may be a flux of low-energy electrons or protons. The second source is impact excitation by electrons from the magnetic conjugate point. The emission due to this source appears to be small immediately after local sunset, rises to a maximum at about 92° conjugate solar zenith angle (CSZA), and then decreases to zero in the vicinity of 105° CSZA. The deduced intensities for this source at 92° CSZA are in the region of 15–30 Rayleighs for local F -layer critical frequencies of 3−2 MHz, respectively.

Measurements with the Sondrestrom radar have been used to examine the daytime thermospheric neutral wind and to relate that wind to other geophysical parameters. Ion drag is found to be particularly important for determining the wind pattern. However, evidence is presented that the wind pattern is significantly influenced by soft particle precipitation and, possibly, by Joule heating.

Sondrestrom radar observations reveal that the dawn-dusk (By) component of the interplanetary magnetic field (IMF) strongly influences the nightside polar convection. This effect is quite complex. The convection for one orientation of By is not the mirror image of the other orientation. A positive By (i.e., pointing toward dusk) seems to organize the velocities such that, at all local times, they are predominantly westward within the radar field-of-view (approximately 68 deg-to-82 deg invariant latitude). Between dusk and midnight, on one such occasion, sunward flow is observed within the polar cap. In the midnight and dawn sectors, when By is negative, the plasma velocities often appear shifted toward early hours such that large southward velocities are observed about 3 hours before midnight. These are the only times when the predominant velocity component is southward.

Processes which confine photoelectrons to the plasmasphere (e.g., collisional backscattering from the thermosphere and magnetic trapping due to pitch angle redistribution through Coulomb collisions in the plasmasphere) tend to increase the steady state photoelectron flux in the plasmasphere above the amplitude level that would otherwise have been attained. Theoretical calculations are presented of steady state photoelectron fluxes in the plasmasphere, for specified atmospheric and ionospheric conditions. (Observational plasma line intensity data for these conditions exist and will be compared elsewhere.) General features of the angular distribution are presented and compared with observations. The transparency of the plasmasphere and the backscattering properties of the thermosphere are investigated. The buildup effect due to collisional backscatter alone is calculated, and the combined buildup effect of pitch angle diffusion and backscatter is estimated. It is found that the inclusion of these effects increases the steady state photoelectron flux amplitude in the plasmasphere by about 50% over the value obtained when the buildup effects are neglected. The calculated steady state photoelectron fluxes in the plasmasphere are in good agreement with the available observations.

When sufficiently high power o-mode HF radio waves are transmitted at frequencies below the ionospheric maximum plasma frequency, not only are plasma instabilities excited, but ambient electrons are accelerated to energies of several electron volts (vs electron thermal energies of order 0.1 eV). Such fluxes have been experimentally inferred from enhancements of atomic oxygen 6300 A, and occasionally 5577 A airglow emission. Active theoretical work has led to conflicting theories for the basic electron acceleration mechanism responsible. We report here the most direct observations to date of such suprathermal electrons. During experiments at Arecibo, transmitting about 140 kW of o-mode power at 7.63 MHz, near but below the ƒ0F2 (exciting strong plasma wave instabilities near an altitude of 285 km) nighttime plasma line intensities were observed to be enhanced by a factor of 10–100. These enhancements extend over a much broader altitude range than that to which HF excited plasma instabilities are confined. When the transmitter was turned off, these plasma line intensities immediately relaxed to their thermal level. Data are presented which should help guide future theoretical development. One significant conclusion that the observations directly lead to is that electrons are accelerated up to at least 20 eV, an energy so high as to call for reassessment of existing published theories. The data also contradict a highly sensitive HF power dependence of the suprathermal electron flux. The production rate is relatively flat from 10 to 20 eV and relatively stable over several hours for constant HF power densities. Model calculations demonstrate that the observed altitude variation of the plasma line intensities is dominated by collisional energy degradation of the suprathermal electron flux to the neutral atmosphere and ionospheric plasma. The modeling also demonstrates that a valid treatment of the plasma physics involved must include some of the geophysical processes (e.g. scattering by the neutral atmosphere).

Simultaneous radar azimuth scans with the Millstone Hill, Sondrestrom, and EISCAT incoherent scatter radars produce maps of the ionospheric convection electric field at high latitudes which span 10 hours of magnetic local time. A series of convection “snapshots” made during an interval of increasing geomagnetic activity indicate that the large-scale convection pattern maintains a two-cell character during substorm onset and that average convection models derived from radar data provide a reasonable representation of the large-scale convection pattern during dynamically varying conditions.

Elevation scan observations made by the Millstone Hill and Sondrestrom incoherent scatter radars are combined to provide extended latitudinal coverage of thermospheric measurements. Maps of the latitudinal and temporal structure of the exospheric temperature are presented for two 24-hour periods over the latitude range 45 to 72 degrees north. On the magnetically quiet June day the Millstone and Sondrestrom data formed a consistent picture of thermospheric structure. On the disturbed July day the two radars observed very different behavior, with Millstone Hill observing strong, long-lived ion frictional heating events but Sondrestrom observing more quiescent behavior. Comparison with HILAT satellite data recorded on the July day suggest that the two radars were observing different ionospheric regions separated by a bright auroral arc with a very turbulent ionosphere to the south of the arc but smooth flow to the north.

The Chatanika radar has been used to measure the ratio of atomic (O+) ions to molecular (O2 +, NO+) ions in the high-latitude ionosphere. The radar results agreed well with simultaneous in situ rocket data, giving confidence in the radar method of deducing ion composition. Measurements made over long periods of time show seasonal variations, diurnal variations, and variations due to auroral processes. The transition altitude, where the number densities of atomic and molecular ions are equal, is a convenient parameter for describing the composition variation with altitude or ‘composition altitude profile.’ The transition altitude occurs at ∼190 km at night and ∼170 km during the day, in agreement with midlatitude results. During the winter the daytime transition altitude is 15 km lower than in summer, a seasonal variation similar to that at midlatitudes. Energetic particle precipitation results in the lowering of the transition altitude, by 10 km in one case when energetic particles deposited ∼20 ergs/cm² s in the atmosphere. The largest variations in ion composition were found during periods of large joule heat input resulting from electric fields on the order of 50 mV/m. The transition altitude increased by 50 km in a case where the joule heat input rate was 30 ergs/cm² s. These observations were compared to calculations from a simple steady state model involving the principal consituents and reactions. The results indicate that the transition altitude during particle precipitation is most influenced by the increased ion production. There do not appear to be significant effects from possible increases of N2 vibrational temperature. A number of interrelated effects contribute to the increase in transition altitude during joule heating. The most important effect is the electric field contribution in raising the effective ion temperature. In addition, it appears that increased N2 density is also required to account for the observed change.