Joshua P. Herron

Retrieval and validation of mesospheric temperatures from Wind Imaging Interferometer observations

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.

Mesospheric temperature observations at the USU/CASS Atmospheric Lidar Observatory (ALO)

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. ALOs 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.

Connection between the midlatitude mesosphere and sudden stratospheric warmings as measured by Rayleigh‐scatter lidar

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.