SA13B-01
SHIMMER on STPSat-1: First Results
The Spatial Heterodyne Imager for Mesospheric Radicals (SHIMMER) is the primary payload of STPSat-1, a small satellite launched in March 2007. SHIMMER measures the solar resonance fluorescence of hydroxyl (OH) and solar scattering from the atmosphere around 309nm, between about 35km and 95km altitude, with a sample spacing of about 2km, covering latitudes of up to 58 degrees. SHIMMER is in a low inclination orbit with a local time precession of about 30min/day which allows the investigation of local solar time effects not possible from satellites in sun synchronous orbits. The main goal of the SHIMMER mission is the investigation of the seasonal and local time dependence of mesospheric OH, which is also a good proxy for water vapor in the upper mesosphere. In addition, SHIMMER observes sunlight scattered by Polar Mesospheric Clouds (PMCs) between ~50N-58N. We will briefly review the basics of Spatial Heterodyne Spectroscopy (SHS), which is the optical technique used by SHIMMER, and the specific design of SHIMMER on STPSat-1. Subsequently, we will present the first hydroxyl data from SHIMMER. We will compare with photochemical model calculations and data from the OH channel of the Microwave Limb Sounder (MLS) on the NASA Aura satellite taken at the same local solar time. SHIMMER is a joint effort between the Naval Research Laboratory and the DoD Space Test Program (SMC/TEL).
SA13B-02
PMC Detection and Mapping Using Aura OMI Measurements
The Ozone Monitoring Instrument (OMI), launched on the NASA Aura spacecraft in July 2004, is a hyperspectral instrument designed to measure stratospheric profile ozone and total column ozone. OMI uses a wide field of view telescope and a CCD detector to observe a 2600 km swath across the orbit track with 13 km x 24 km pixels at the surface for nadir measurements (13 km x 48 km at UV wavelengths), while simultaneously collecting spectral information over the wavelength range 264-511 nm for each pixel. These measurements provide full global coverage every day at the latitudes where polar mesospheric clouds (PMCs) occur, with substantial overlap between consecutive orbits. We have successfully adapted the PMC detection algorithm developed for SBUV and SBUV/2 measurements for use with OMI Level 1B data. These results demonstrate a factor of 100- 200 increase in PMC detections, significantly improved resolution of horizontal structure, and greater dynamic range compared to concurrent SBUV/2 data. These improvements are due to the expanded OMI cross-track coverage and smaller pixels compared to SBUV/2 (nadir only, 170 km x 170 km). Overlapping OMI measurements from multiple consecutive orbits allow us to examine local time variations in PMC brightness and frequency for any location above 70 degrees latitude on a daily basis. Additional refinements to the OMI algorithm will take further advantage of its increased wavelength coverage and scattering angle sampling. OMI has smaller pixels and better wavelength sampling than SBUV/2 instruments, providing much improved information for PMC particle size analysis. PMC maps from OMI will also provide an important validation resource for the NASA AIM (Aeronomy of Ice in the Mesosphere) mission, launched on 25 April 2007.
SA13B-03
Long-Term Variations in PMC Frequency as a Function of Latitude from SBUV
An earlier analysis of the Polar Mesospheric Cloud (PMC) measurements from the Solar Backscatter Ultraviolet (SBUV & SBUV/2) satellite measurements found that there was a weak long-term increase in the frequency of occurrence of PMCs, which was not statistically significant [DeLand et al. 2003]. Since then, a new Version 3 data set has been developed using an improved PMC detection algorithm which produces more consistent results under all measurement conditions. DeLand et al. [2007] have used this new data set to examine the long-term variations in the PMC brightness. We have utilized this Version 3 data set to examine the corresponding long- term variations in the PMC frequency as a function of latitude. The occurrence frequency data are adjusted for local time effects before merging the overlapping data sets from different SBUV/2 instruments for trend calculations. Preliminary results indicate that while there is a positive trend in all latitude bins, the trend was only about 6% per decade in the lowest latitude bin (50° to 64°) in both hemispheres, and was not statistically significant. At higher latitudes (64° to 74°, and 74° to 82°) the trend was much stronger in both hemispheres (approximately 15% to 25% per decade), and statistically significant. There is also a strong anti-correlation with the long-term variation of solar Lyman-alpha flux, with a peak-to-peak solar cycle variation of approximately a factor of 2 for all latitudes. The weak long-term increase at 50° to 64° N is comparable with that found in the ground based Noctilucent Cloud (NLC) observations for Northern Europe recently updated by Kirkwood et al. [accepted by Ann. Geophys., 2007].
SA13B-04 INVITED
The Aeronomy of Ice in the Mesosphere Mission: Overview and Early Results
The Aeronomy of Ice in the Mesosphere (AIM) mission was launched from Vandenberg Air Force Base in California at 1:26:03 PDT on April 25, 2007 becoming the first satellite mission dedicated to the study of noctilucent clouds. A Pegasus XL rocket launched the satellite into a near perfect 600 km sun synchronous circular orbit. AIM carries three instruments - a nadir imager, a solar occultation instrument and in-situ cosmic dust detectors - that were specifically selected because of their ability to provide key measurements needed to address the six AIM science objectives. Brief descriptions of the science, instruments and observation scenario will be presented along with early science results.
SA13B-05 INVITED
Modelling of Summer Mesopause PMC Formation With LIMA
No abstract.
SA13B-06
Mesospheric Simulations with the NOGAPS-ALPHA model: Applications to the Summer Polar Mesosphere and AIM data
The Navy Operational Global Atmospheric Prediction System (NOGAPS), the Department of Defense's global numerical weather prediction (NWP) system, consists of two main components: the Naval Research Laboratory (NRL) Atmospheric Variational Data Assimilation System (NAVDAS) and a global spectral general circulation model (GCM) for forecasting. NRL researchers are currently developing an Advanced-Level Physics High-Altitude (ALPHA) NOGAPS prototype that extends the currently operational 1 hPa upper boundary of NOGAPS through the mesosphere and lower thermosphere (MLT) to ~110 km. We report results of preliminary experiments with this NOGAPS-ALPHA system during May-June 2007, focused on the northern hemisphere (NH) summer mesosphere observed from the Aeronomy of Ice in the Mesosphere (AIM) satellite. These AIM-period NOGAPS-ALPHA experiments have two main goals: to provide global modeling support for AIM science and to allow objective validation of these new NOGAPS-ALPHA MLT fields using independent observations from AIM. We report results of runs which assimilate temperature and water vapor data from the SABER and MLS instruments up to ~0.01 hPa. We investigate the development of the cold NH summer mesopause in NOGAPS-ALPHA and its sensitivity to parameterized nonorographic gravity wave drag (GWD) and radiative heating/cooling by comparing with temperatures and water vapor measured by AIM's SOFIE instrument. We can also compare the variability in the NOGAPS-ALPHA temperature and water vapor fields with mesospheric cloud occurrence statistics measured by CIPS on AIM.
SA13B-07
Simulation of Polar Mesospheric Clouds Within a 3-Dimensional Chemistry Climate Model
While cold mesospheric temperatures dictate that polar mesospheric clouds (PMC) will usually form during the summer months, substantial variation in their global frequency and distribution has been observed by both ground-based and satellite instruments. Likely sources of PMC variability include global-scale dynamics, solar irradiance changes, and long-term trends in atmospheric constituents and temperatures. To explore this variability, a parameterization of PMC microphysics has been incorporated into NCAR's Whole Atmosphere Community Climate Model (WACCM), a chemistry climate model the covers the height range from the surface to ~130 km. This paper describes the parameterization, explores PMC variability in the model, and presents comparisons of WACCM PMC frequency and ice mass distributions with observations from instruments on board the Aeronomy of Ice in the Mesosphere and Student Nitric Oxide Explorer satellites.
SA13B-08
Numerical simulations of the three-dimensional distribution of polar mesospheric clouds using WACCM/CARMA
Polar mesospheric clouds (PMC) are ice clouds that routinely form in the cold summer mesopause region; however, the nucleation mechanism for these clouds is not well understood. Several possible condensation nuclei have been identified including: meteoric dust, ion clusters, sulfate aerosols, soot, sodium bicarbonate and sodium hydroxide. Recent studies have shown that fewer large meteoric dust particles may be present in the summer mesopause region than have previously been assumed to be necessary for the nucleation of PMCs. We use WACCM/CARMA, a three-dimensional chemistry climate model based upon the Whole-Atmosphere Community Climate Model (WACCM) with sectional microphysics from the Community Aerosol and Radiation Model for Atmospheres (CARMA) to study the distribution and characteristics of PMCs formed by heterogeneous nucleation with meteoric dust particles. The distribution of meteoric dust particles in the model is also calculated using sectional microphysics and is based upon a source of recondensed material from the ablation of micrometeoroids. Results from these simulations are compared with several observations including those from the Aeronomy of Ice in the Mesosphere (AIM) mission, the Solar Backscatter Ultraviolet (SBUV) instrument and the Student Nitric Oxide Explorer (SNOE) satellite and with results from other models.