SA53D-01
High resolution Polar Mesospheric Cloud images from the Cloud Imaging and Particle Size Experiment: Implications for cloud appearance and ice particle growth
The Cloud Imaging and Particle Size (CIPS) Experiment on the Aeronomy of Ice in the Mesosphere Mission (AIM) has the ability to image Polar Mesospheric Clouds (PMC) with approximately 2 km resolution. In addition, the CIPS has a large field of view that allows the same region of space (at high latitude) to be viewed on several successive orbits with a cadence of about ninety minutes. The overlapping CIPS data reveal significant variations in PMC albedo and occurrence from orbit to orbit, with bright clouds containing relatively large particles appearing in regions that were essentially cloud free ninety minutes earlier. The implications for PMC growth and lifetimes are discussed with respect to modeling results. In addition, the high resolution data provide a new view of clouds and reveal longitudinal variability in cloud structure that at times resembles near-coherent wave patterns, and at times is dominated by circular cloud features. It is suggested that this variability is associated with longitudinal variations in gravity wave activity.
SA53D-02
PMC Variability Observed in Aura OMI Data
The Ozone Monitoring Instrument (OMI) is a hyperspectral nadir-viewing spectrometer that has been flying on the EOS Aura spacecraft since July 2004. OMI data cover the spectral range 265-500 nm, and can be analyzed using a modified version of the Solar Backscatter Ultraviolet (SBUV) polar mesospheric cloud (PMC) detection algorithm. OMI's smaller pixel size (13 km x 48 km at nadir) and 110° cross-track viewing geometry allow observations for 6-8 consecutive orbits at most locations between 70° and 90° latitude on a daily basis. This provides us with the opportunity to directly observe PMC local time variability and evaluate its dependence on latitude and longitude. Results from four PMC seasons in each hemisphere will be presented. OMI is also the first instrument to make regular PMC measurements up to 90° latitude in both hemispheres. We will discuss how results obtained from the extended OMI spatial coverage compare with predicted near-polar behavior from previous measurements.
SA53D-03
First Climatology of Polar Mesospheric Clouds From GOMOS/ENVISAT Stellar Occultation Instrument.
GOMOS on board the European platform ENVISAT is a stellar occultation instrument combining 4 spectrometers in the spectral range 250 to 950 nm (UV-visible- near IR) and 2 fast photometers. On the day side, GOMOS measures also the solar light scattered by the atmosphere. In the summer polar day, polar mesospheric clouds (PMC) are clearly detected using the photometers signals. The observation of PMC with the spectrometers provides the spectral dependence of the scattering by PMC particles from which it is possible to derive some information on particle size. The sun-synchronous orbit of ENVISAT allows observing PMC in both hemispheres. The stellar occultation technique allows a very accurate determination of the tangent altitude of the ray path (better than 100 m). The method of detection will be described and the climatology of PMC obtained by GOMOS will be presented, focusing on the seasonal and latitudinal coverage, the asymmetry between hemispheres and the determination of the mean altitude.
SA53D-04
The Mobile Scanning Iron Lidar: A new Approach for Background Free Doppler Measurements of Rayleigh/Mie/Resonance Scattering at Daylight.
At daylight measurements in the UMLT are hindered by the strong solar background. Nowadays lidars reject a part of the background by narrow band spectral filtering where the spectral width is on the order of the Doppler width of the backscattered signal. Spectral filtering alone reduces the background largely but the remaining background is still several orders of magnitude larger compared to night time observations. In recent years we have therefore developed a new type of Doppler resonance lidar, namely a scanning iron lidar. Compared to up-to-date potassium and sodium lidars the iron lidar provides 2-3 orders of magnitude lower background for resonance scattering and additionally performs simultaneously background free observations of aerosols from the stratosphere to the mesosphere. In July 2008 the instrument was installed closed to ALOMAR at 69° N for temperature measurements during the ECOMA campaign. After the campaign the instrument was operated by remote control with very little onsite assistance. The transition in temperature from summer to winter is covered. We will compare these measurements with the temperatures of the former potassium lidar at Spitsbergen (78° N) and the FS-climatologies at 69° N (Lübken JGR 99) and 78° N (Lübken and Müllemann JGR, 2003).
SA53D-05
Long term trends of PMC/NLC modeled with LIMA-ICE
In this paper we investigate the long term trend of mesospheric ice layers (NLC/PMC) by means of a model study with LIMA-ICE (Leibniz Middle Atmosphere Model and ICE Model). We take into account 3 decades of northern and southern mesospheric summers from 1979 up to 2008, a total of more than 60 PMC seasons, and compute the mean occurrence, altitude, and brightness of each PMC season. Each summer season has individual mesospheric temperatures, dynamics, water vapor concentrations, and Lyman-alpha conditions computed by the LIMA-GCM. As as result, the analysis of PMC trend behaviour show that the parameters occurrence, brightness, and altitudes can be used to detect a trend signal in PMC/NLC formation. In our paper we will present comparisons of our model results to satellite time series (SBUV) and lidar measurements over ALOMAR. Especially, we will investigate the different roles of possible trends of background mesopause temperatures and water vapor combined with solar cycle conditions, and their effect on NLC/PMC trends.
SA53D-06
The influence of the winter hemisphere on polar mesospheric clouds
Polar mesospheric cloud (PMC) observations have revealed that a significant part of the year-to-year variability in the polar summer mesosphere is forced by the planetary wave activity in the winter stratosphere. This inter-hemispheric coupling may also explain hemispheric differences in the characteristics of these high altitude clouds. We investigate the extent to which conditions in the winter hemisphere determine the state of the summer mesopause region using observations of PMCs from the Aeronomy of Ice in the Mesosphere (AIM) satellite in combination with model results from the Whole Atmosphere Community Climate Model (WACCM). PMC parameters of interest include the spatial extent of the cloud cover and the temporal PMC variability over the summer season. In this paper we focus on the start and end of the PMC seasons and connect these to the build-up and breakdown of the polar vortex in the winter hemisphere. We also examine a specific case of a major stratospheric warming to see how it affects the polar mesospheric cloud cover in the opposite hemisphere.