SA43A-1557
Microphysical studies of mesospheric sulfate aerosol as PMC nuclei in WACCM3
We present new three-dimensional calculations of the mesospheric sulfate layer, a class of particles which have been suggested as a source of nuclei for polar mesospheric clouds (PMCs). Recent modeling studies have raised questions about whether sufficient number densities of meteoritic dust particles large enough to nucleate PMCs can exist in PMC nucleation regions. By contrast, our calculations show that sulfates should grow on the smaller dust particles in these cold regions, creating nuclei of sufficient size and number density to account for observed PMCs. We have incorporated sulfur chemistry and aerosol microphysics into the Whole Atmosphere Community Climate Model 3 (WACCM3), a comprehensive model that spans the range of altitude from the Earth's surface to the thermosphere. We have tuned the gravity wave parameterization in WACCM3 to reproduce well observed temperatures in the mesopause region that are critical to PMC and sulfate formation, and present sensitivity studies for such tunings. Our calculations show that where temperatures are coldest and meteoritic dust is present, sulfates will grow on them. We discuss the feasibility of observing mesospheric sulfates containing dust cores with the Solar Occultation For Ice Experiment (SOFIE) on board NASA's current Aeronomy of Ice in the Mesosphere (AIM) experiment. To date, AIM has provided nearly two years of observations of PMCs.
SA43A-1558
Sensitivity of WACCM/CARMA simulations of polar mesospheric clouds to gravity wave and microphysics parameterizations
We use WACCM/CARMA to explore the sensitivity of simulations of polar mesospheric clouds (PMCs) to changes in the parameters and processes that impact the cloud microphysics. WACCM/CARMA is 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). We look at the response of the model to changes in the gravity wave parameterization, the ice particle nucleation scheme and the specification of radiative heating of the cloud particles. These results are compared with cloud properties retrieved from the Solar Occultation for Ice Experiment (SOFIE) and the Cloud Imaging and Particle Size Experiment (CIPS) instruments from the Aeronomy of Ice in the Mesosphere (AIM) mission. We find that the simulated cloud properties generally agree well with both SOFIE and CIPS observations and are very sensitive to the gravity wave parameterization. We see similar results for a variety of nucleation parameters and find radiative heating to be necessary to get a mid-season reduction in PMCs that is seen in the observations.
SA43A-1559
Ice content of polar mesospheric clouds from the AIM mission: Comparison with the WACCM general circulation model
The Aeronomy of Ice in the Mesosphere (AIM) satellite mission has observed three polar mesospheric cloud (PMC) seasons at this point in time including two in the northern hemisphere (2007 and 2008) and one in the south (2007/2008). The Cloud Imaging and Particle Size (CIPS) and Solar Occultation for Ice (SOFIE) instruments observe PMC from a noon-midnight sun-synchronous orbit. CIPS and SOFIE measure the UV scattering and IR extinction of PMC, respectively. The two experiments provide separate measurements of the integrated (vertical column) ice water content, independent of knowledge of the particle size distribution. We present results for the total ice content of the 2007 summertime polar mesosphere, and compare with predictions from two models that simulate PMC within version 3 of the Whole Atmosphere Community Climate Model (WACCM-3). The models differ in that one includes a sectional microphysics representation of the PMC size distribution, using the Community Aerosol and Radiation Model for Atmospheres (CARMA), while the other uses a bulk microphysics representation. Seasonal and latitudinal cross-sections show good overall agreement with both models, indicating a significant advance in understanding the complicated interactions of ice microphysics, chemistry and dynamics in the summer polar mesosphere.
SA43A-1560
The PMC Mass for the 2007 Northern Summer: Results From a Microphysical Model Driven by a Data Assimilation System
An Advanced-Level Physics High-Altitude (ALPHA) prototype of the Navy Operational Global Atmospheric Prediction System (NOGAPS) has recently been extended into the upper mesosphere, providing synoptic analysis fields in support of NASA's Aeronomy of Ice in the Mesosphere (AIM) mission. Microphysical model results have indicated that temperature (T) and water vapor (H2O) are critical to the calculation of the polar mesospheric cloud (PMC) ice mass. NOGAPS-ALPHA assimilates T up to ~88 km altitude from NASA's Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) and Microwave Limb Sounder (MLS) satellite experiments and H2O mixing ratios to the same height from MLS for the 2007 northern summer. The analyzed T and H2O fields provide a measure of the local saturation, which strongly correlates with PMC occurrence observed independently by the Solar Occultation For Ice Experiment (SOFIE) on AIM. Motivated by this fact, we seek to quantify the relationship between the mesospheric environment (T, H2O) and the PMC mass. Our approach is to use time-dependent output from NOGAPS-ALPHA in the one-dimensional Community Aerosol and Radiation Model for Atmospheres (CARMA) to simulate the microphysics and compare the results directly to SOFIE observations. We will focus primarily on the PMC mass during the 2007 northern summer and its sensitivity to available nucleation sites. Although meteoric smoke is regarded as the most likely nucleation site for PMCs, recent results from global climate models indicate that the distribution of meteoric smoke in the polar summer mesosphere is significantly less than expected. We will explore the sensitivity of our results to variations in concentrations of meteoric smoke and identify what is needed to reproduce the SOFIE observations.
SA43A-1561
QBO Generated Inter-annual Temperature Variations and their Solar Cycle Modulation in the Polar Mesopause Region
We present results from the Numerical Spectral Model (NSM), which focus on the temperature environment of the mesopause region where Polar Mesospheric Clouds (PMC) form. The dynamical interactions originate from the stratospheric Quasi-biennial Oscillation (QBO) of the zonal circulation, which is generated in the NSM primarily by parameterized small-scale gravity waves (GW) and by planetary waves owing to the baroclinic instability. In contrast to the zonal winds that are confined to low latitudes, the associated temperature variations extend to high latitudes and in particular at higher altitudes. The meridional circulation redistributes the energy, and one can show that the associated vertical winds produce through adiabatic heating and cooling inter-annual year-to-year temperature variations from 5 to 10 K in the polar mesopause region. Our analysis also demonstrates that the non-linear interaction between the QBO and the dominant annual cycle produces significant inter-hemispheric differences. Salby and Callaghan (J. Clim. 2000) analyzed 41 years of radiosonde measurements at 20 km and found in the QBO zonal winds a relatively large (~ 8 m/s) solar cycle (SC) modulation. This observation was reproduced in a study with the NSM where the amplitude of the imposed SC varies with height exponentially from 0.2% at the ground to 20% at 100 km and above (Mayr et al., GRL, 2006). That model also generates QBO (inter-annual) temperature variations in the polar mesopause region but with a measurable SC modulation. Over the 10-year period of the imposed SC forcing, the QBO temperature amplitude varies on average by more than 1 K in the polar region, depending on the hemisphere. And the phase of the QBO temperature modulation, relative to the SC peak, can vary by up to 3 years.
SA43A-1562
The Transfer Function Model (TFM) as a Tool for Simulating Gravity Wave Phenomena in the Mesosphere
The Transfer Function Model (TFM) is semi-analytical and linear, and it is designed to describe the acoustic gravity waves (GW) propagating over the globe and from the ground to 600 km under the influence of vertical temperature variations. Wave interactions with the flow are not accounted for. With an expansion in terms of frequency-dependent spherical harmonics, the time consuming vertical integration of the conservation equations is reduced to computing the transfer function (TF). (The applied lower and upper boundary conditions assure that spurious wave reflections will not occur.) The TF describes the dynamical properties of the medium divorced from the complexities of the temporal and horizontal variations of the excitation source. Given the TF, the atmospheric response to a chosen source is then obtained in short order to simulate the GW propagating through the atmosphere over the globe. In the past, this model has been applied to study auroral processes, which produce distinct wave phenomena such as: (1) standing lamb modes that propagate horizontally in the viscous medium of the thermosphere, (2) waves generated in the auroral oval that experience geometric amplification propagating to the pole where constructive interference generates secondary waves that propagate equatorward, (3) ducted modes propagating through the middle atmosphere that leak back into the thermosphere, and (4) GWs reflected from the Earth's surface that reach the thermosphere in a narrow propagation cone. Well-defined spectral features characterize these wave modes in the TF to provide analytical understanding. We propose the TFM as a tool for simulating GW in the mesosphere and in particular the features observed in Polar Mesospheric Clouds (PMC). With present-day computers, it takes less than one hour to compute the TF, so that there is virtually no practical limitation on the source configurations that can be applied and tested in the lower atmosphere. And there is no limitation on the temporal and spatial resolutions the model simulations can provide. We shall discuss the concept and organization of the TFM and present samples of GW simulations that illustrate the capabilities of the model and its user interface. We shall discuss in particular the waves that leak into the mesopause from the thermosphere above and propagate into the region from tropospheric weather systems below.
SA43A-1563
Longitudinal variability of Polar Mesospheric Cloud (PMC) albedo and frequency from the Cloud Imaging and Particle Size Experiment: Comparison of the 2007 and 2008 Northern Hemisphere cloud seasons
The Cloud Imaging and Particle Size (CIPS) Experiment on the Aeronomy of Ice in the Mesosphere Mission (AIM) images Polar Mesospheric Clouds (PMCs) as a function of latitude and time. Data on PMC albedo and occurrence frequency have now been taken over two Northern Hemisphere seasons for 2007 and 2008 and one Southern season, 2007/2008. The data for the 2007 and 2007/2008 seasons have shown strong longitudinal variability of albedo and occurrence when averaged over periods of 15 to 20 days that are correlated to ice water content from the Solar Occultation for Ice Experiment (SOFIE) on AIM, and anti- correlated to temperature data from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) and to the occurrence of gravity waves. We compare the time and longitudinal variations of cloud albedo and frequency of occurrence and temperature for the three seasons.
SA43A-1564
Longitudinal variability in PMC structures observed from the CIPS experiment on the AIM spacecraft: Impact on PMC occurrence frequency and brightness.
The Cloud Imaging and Particle Size (CIPS) experiment is one of three instruments on board the Aeronomy of Ice in the Mesosphere (AIM) spacecraft that was launched into a 600 km sun-synchronous orbit on April 25, 2007. CIPS images have shown clear and distinct wave patterns and structure in Polar Mesospheric Clouds (PMCs), around the summertime mesopause region, which are qualitatively similar to ground based photographs of Noctilucent Clouds (NLCs). These structures, observed in PMCs, are interpreted as manifestations of upward propagating gravity waves. One of the objectives of the AIM mission is to investigate gravity wave effects on PMC formation and evolution. In this presentation we provide new results pertaining to the longitudinal variability of observed PMC wave structures from CIPS. The horizontal scales and maps of the observed PMC structures during the northern and southern hemisphere 2007 and 2008 cloud seasons are presented. By comparing the longitudinal variability of the normalized wave occurrence frequency with the CIPS observed PMC occurrence frequency and albedo we can infer new details about the effect of gravity waves on PMCs. The spatial variability of the observed longitudinal structures and correlation with topography are also presented.
SA43A-1565
Investigating Gravity Waves Measured by CIPS/AIM in the Northern/Southern Summer Polar Mesosphere
The Aeronomy of Ice in the Mesosphere (AIM) satellite was launched on April 25, 2007. Its primary goal is to explore Polar Mesospheric Clouds (PMC) near the mesopause region, and investigate their formation and evolution. One of the instruments onboard AIM is the Cloud Imaging and Particle Size (CIPS), which is a four camera, wide-field (120° x 80°) UV imager designed to measure PMC morphology and particle sizes. Initial investigations using CIPS imagery have revealed a variety of cloud and wave-like structures, the latter due primary to gravity waves with a broad range of scale-sizes. Recently developed high resolution CIPS data (2x2 km pixel resolution) provide high quality images of PMCs, facilitating more detailed analysis of wave structures in the clouds. The effects of differing gravity wave sources in the northern and southern hemispheres on PMC visibility and structure are not yet known. In this presentation, we compare and contrast wave spectra obtained from CIPS data during the first summer season for both the northern (July, 2007) and southern (January, 2008) polar regions (utilizing the high resolution CIPS level 2a data), focusing on wave occurrence and dominant horizontal scale-sizes.
SA43A-1566
Detection of mesospheric gravity waves in Odin/OSIRIS PMC data in 2002- 2008
The Optical Spectrograph and InfraRed Imager System instrument (OSIRIS) on the limb-viewing Odin satellite observes Polar Mesospheric Clouds (PMCs) in both hemispheres since November, 2001. The orbit period of Odin is 96 minutes and the maximum latitudinal coverage in the orbit plane is between 82.2 N and 82.2 S. In this work, the longitudinal distribution of Odin/OSIRIS PMC brightness in each hemisphere during a 4-week period around the summer solstice from 2002 until 2008 is analysed. In the Northern Hemisphere, the PMC brightness around 60+-20 W and around 80+-20 E is up to 30 percent lower than that at other longitudes. In the Southern Hemisphere, the cloud brightness is also 30-60 percent lower around 80+-20 W. We attribute this effect to the influence of gravity waves generated by the Earth's terrain above Greenland and Ural mountains (the natural boundary between Europe and Asia) in the Northern Hemisphere and by the Antarctic Peninsula mountains in the Southern Hemisphere.
SA43A-1567
The Odin satellite polar mesospheric noctilucent cloud database
The Odin satellite has so far provided 13 seasons of noctilucent cloud observations. Odin is now run as an ESA Third Party Mission and data are made available within this framework. This report describes the noctilucent cloud data product as obtained from the Optical Spectrograph and Infrared Imager System (OSIRIS). The analyzed data comprise cloud ocurrence, brightness, and particle size. Odin's mesospheric observation programme has successively been extended and offers today daily measurements during the noctilucent cloud season. Odin's latitude coverage is unique with measurements all the way to the pole in the southern hemisphere. Odin noctilucent cloud data provide thus an excellent basis for studies of spatial, seasonal and interannual variability, hemispheric differences, and dynamical influences on the polar summer mesopause. Co-analysis with other satellite and ground-based observations is ongoing.
SA43A-1568
In Flight Calibration Monitoring of the CIPS UV Imager Using Atmospheric Rayleigh Scattered Radiance
The Cloud Imaging and Particle Size (CIPS) instrument is a nadir viewing UV imager flying aboard the Aeronomy of Ice in the Mesosphere (AIM) satellite. AIM is at an altitude of approximately 600 km and CIPS has a field of view of approximately 120° along orbit track by 80° across orbit track. This results in a field of view of approximately 2000 km by 1000 km. CIPS observes with a center wavelength at 265.8 nm with a 16.5 nm FWHM with a resolution near nadir of approximately 1 km by 2 km. We describe a method to use the atmospheric Rayleigh scattered radiance observations taken at fast cadence to derive the relative sensitivity across the camera (the flat field). Although the Raleigh scattered UV radiance is highly dependent upon geometry and the mesospheric ozone column abundance, our technique removes the requirement for knowledge of ozone parameters. By taking consecutive images at fast cadence we observe the same geophysical locations, having the same ozone parameters, at many locations across the camera. Observations of the same location with the satellite observing from opposite sides along track from the point of observation will have the same geometry parameters, thus these pairs of observations observe the same phase function adjusted albedo independent of the ozone parameters. The ratio of these measurements is effectively a direct measurement of the relative calibration between the two sets of pixels. After repeating this experiment with the satellite pitched, we string the pairs of pixels together to derive a relative calibration between the pixels in along track strips. In this talk we will present the observation and calibration techniques. We will show that this is a generally applicable technique in the UV and is resistant to systematic trends in the flat field.
SA43A-1569
An Analysis of PMC Detection Sensitivity for the CIPS Instrument
The Cloud Imaging and Particle Size (CIPS) instrument is a nadir-viewing UV imager aboard the Aeronomy of Ice in the Mesosphere (AIM) satellite. CIPS measures scattered solar radiation at 265 nm using a unique four-camera configuration providing an instantaneous field of view of 120o (along-track) by 80 o (cross- track). Full instrument resolution for nadir pixels is 1 by 2 km. By combining data from multiple cameras, CIPS observes a given volume of air at seven different scattering angles ranging from 20 to 180 degrees. Level 4 data processing, which includes PMC detection and cloud parameter retrievals, typically uses binned data with a spatial resolution of 5 x 5 km. The detection algorithm discriminates a PMC signature from the Rayleigh-scattered background by exploiting the fact that the former is strongly forward scattered, whereas the background signal is symmetric about 90 degrees scattering angle. We present an analysis of the CIPS cloud detection sensitivity, with the goal of deriving an effective cloud brightness (albedo) threshold. This threshold is expected to vary with solar zenith angle (and hence latitude) due to both the CIPS measurement sampling characteristics and the geophysical variation in the Rayleigh background. Simulations show that it also depends on the mean cloud particle radius, as well as the desired spatial resolution of the cloud product (data binning). By quantifying these dependencies we can account for the residual effects of varying detection sensitivity in interpreting the cloud occurrence frequencies observed by CIPS, particularly the latitude dependence. This understanding will also provide a quantitative foundation for comparing the CIPS observations with other data sets. We also compare the sensitivity of the operational CIPS algorithm with an alternative cloud detection algorithm similar to that used for SBUV PMC analysis. This technique uses the measured albedo directly from individual CIPS pixels at a fixed scattering angle. Cloudy pixels are detected as enhancements above a background level, which is obtained iteratively by fitting a polynomial curve to an entire orbit's worth of data. This approach is found to work best at lower latitudes, which is precisely where the operational algorithm encounters its greatest difficulty due to increased brightness of the Rayleigh background and decreased measurement sampling of forward scattering angles. Thus results from this analysis may be used to define an optimal method for combining these two techniques in routine CIPS data processing.
SA43A-1570
Scattering Phase Functions and Particle Sizes for Polar Mesospheric Clouds from the Aeronomy of Ice in the Mesosphere (AIM) Explorer
The Cloud Imaging and Particle Size (CIPS) instrument on the AIM spacecraft is a 4-camera nadir pointed imager with a bandpass centered at 265 nm and a field of view of 120 by 80 degrees. CIPS observes Polar Mesospheric Clouds (PMCs) against the sunlit Rayleigh-scattered background. At individual polar locations approximately 5km by 5km in area, CIPS observes the same volume of air multiple times over a range of scattering angles from about 35 to 150 degrees. These multi-angle observations allow the identification and extraction of the PMC scattered radiance from the Rayleigh-scattered background. Ice phase functions have been obtained throughout the polar cap for two full northern PMC seasons and most of one southern season. We will overview the spatial and temporal variability of the measured phase functions and compare the results for the northern and southern seasons. With assumptions about the shape of the ice particles, the PMC phase functions yield mean particle radius. We will report on the spatial and temporal variability of the particle radii. In particular we will focus will be on times and locations observed by both CIPS and SOFIE. Comparisons between CIPS and SOFIE particle size detections will be presented.
SA43A-1571
Simultaneous Observations of NLC From Space and From Ground.
Noctilucent Clouds (NLC) have been extensively observed and characterised from the ground since their first identification in 1885. It has been argued that NLC first appeared just around this time and that they are important indicators for atmospheric changes and variability. More recently it has also been demonstrated that NLC properties and occurrence frequency are intimately related to the dynamic coupling processes on global scale. Noctilucent clouds were first detected from space by an instrument on the OGO-6 satellite in 1972. It was also discovered that a permanent scattering layer exists over the polar cup during the summer. NLCs are now considered to be equatorward extenstions of this permanent layer, also sometimes called Polar Mesospheric Clouds (PMC). More recently NLC/PMC have been extensively studied by the Swedish satellite Odin launched in 2001. The AIM satellite mission, launched in 2007, is entirely dedicated to research into noctilucent clouds. The Cloud Imaging and Particle Size (CIPS) experiment on AIM is a wide angle (120° along track by 80° across track) imager consisting of four identical cameras arranged in a cross pattern. CIPS is the first space borne instrument that takes images of PMCs with a high spatial resolution and in the viewing geometry that makes comparison with the ground imagery possible. Since the summer 2004, photographs of noctilucent clouds (NLC) are taken from a site in Stockholm, Sweden (59.37°N, 18.06°E). A digital camera takes every summer night hundreds of images of twilight sky at the rate of 1 to 2 pictures per minute. A technique to re-projected these images to a horizontal plane in order to correctly represent movements and actual spatial scales have been developed. Simultaneous observations of the same NLC scene from space and from ground will be presented and discussed.
SA43A-1572
Comparison of Satellite and Ground-based Measurements of Polar Mesospheric Clouds
Polar Mesospheric Clouds (PMCs) are tenuous ice clouds that form near the cold (<150K) summer mesopause region (80-85 km). From the ground, these clouds are seen during twilight hours as Noctilucent or "night shining" Clouds (NLCs) and are typically seen from latitudes from 50° to 65°. Observations by the Solar Backscatter Ultraviolet (SBUV) instruments on the NOAA satellites have shown that the occurrence and brightness of NLCs have been increasing over the last several decades prompting speculation concerning their possible role in climate change. Recently the Aeronomy of Ice in the Mesosphere (AIM) satellite was launched (April 2007) and is the first satellite dedicated to the study of NLCs. In this presentation, we compare SBUV and AIM PMC observations with ground-based image data collected during two campaigns from Edmonton, Canada (June 30-July 17, 2007) and Delta Junction, Alaska (July 29- August 17, 2007). Four nights of data are presented where coincident measurements were obtained by AIM, SBUV and ground-based imagers. The results show good spatial or temporal agreement, but rarely both, and illustrate the importance of coordinated measurements for better understanding the geographic and local time variability of PMCs.
SA43A-1573
Drivers for the Formation and Variability of Ice Layers in the Mesopause Region
We provide an overview of the latest three Polar Mesospheric Cloud (PMC) seasons as seen by the Aeronomy of Ice in the Mesosphere (AIM) Cloud Imaging and Particle Size (CIPS) experiment: the northern 2007 and 2008 seasons as well as the southern 2007/2008 season. These PMC results will be based on an algorithm similar to the Solar Backscatter Ultraviolet instrument (SBUV) algorithm and thus they facilitate a comparison to concurrent and historical SBUV data. Correlations between PMC data and measurements of temperature and water vapor from different satellite instruments such as the Microwave Limb Sounder (MLS) are used to investigate mechanisms contributing to PMC variability. To evaluate our understanding of the forcing variables underlying these mechanisms, we will compare simulations of mesospheric meteorology from the Whole Atmosphere Community Climate Model (WACCM) to satellite measurements.
SA43A-1574
Temperature Trends in the Polar Mesosphere between 2002--2007 using TIMED/SABER Data
The TIMED Satellite was launched on December 7, 2001 to study the dynamics and energy of the mesosphere and lower thermosphere. The TIMED/SABER instrument is a limb scanning infrared radiometer designed to measure a large number of minor constituents as well as the temperature of the region. In this study, we have concentrated on the polar mesosphere, to investigate the temperature characteristics as a function of spatial and temporal considerations. We used the recently revised SABER dataset (1.07) that contains improved temperature retrievals in the Earth polar summer regions. Weekly averages are used to make comparisons between the winter and summer, as well as to study the variability in different quadrants of each hemisphere. For each year studied, the duration of polar summer based on temperature measurements compares favorably with the PMSE (Polar Mesospheric Summer Echoes) season measured by radar at the ALOMAR Observatory in Norway (69°N). The PMSE period should also define the summer period suitable for the occurrence of polar mesospheric clouds. The unusual short and relatively warm polar summer in the northern hemisphere during 2002 is also clearly defined in this analysis and shown to be unique for the period analyzed.
SA43A-1575
Temperature and water vapor measured by SABER/TIMED and implications for mesospheric ice clouds
The SABER instrument on board the TIMED Satellite is a limb scanning infrared radiometer designed to measure temperature and minor constituent vertical profiles and energetics parameters in the mesosphere and lower thermosphere. We applied an updated non-LTE model for the interpretation of the 6.3 micron H2O radiance measured by SABER. The obtained meridional and seasonal distributions of the H2O density in the mesosphere are discussed. The conditions for the mesospheric ice particle formation are estimated using the combination of SABER H2O and temperature (V1.07) profiles.
SA43A-1576
Preliminary Validation of AIM SOFIE Water Vapor Observations and Seasonal Evolution During the PMC season
The Aeronomy of Ice in the Mesosphere satellite was launched on April 25, 2007 becoming the first mission dedicated to the study of Polar Mesospheric Clouds (PMCs). AIM has observed three PMC seasons at this point in time including two in the northern hemisphere and one in the south. The Solar Occultation for Ice Experiment (SOFIE) measures vertical profiles of temperature and trace gases involved in the PMC microphysics along with a number of PMC properties. Water vapor is central to PMC formation as it is now clear that the clouds are made up primarily of water ice. This paper describes the SOFIE water vapor measurement characteristics, presents measured vertical profiles and shows results of comparisons with ACE and MLS. Evolution of water vapor over the course of the PMC season in both hemispheres and comparisons of changes for the two northern seasons will be discussed.
SA43A-1577
SOFIE Measurements of PMCs, Water Vapor, and Temperature
The Solar Occultation For Ice Experiment (SOFIE) onboard the AIM satellite has completed measurements of
two northern and one southern polar mesospheric cloud (PMC) seasons, and continues routine operation.
This work describes results using the record of SOFIE PMC, temperature, and water vapor measurements.
SOFIE temperatures are now based on non-local thermodynamic equilibrium retrievals, and are up to 10 K
cooler than previous SOFIE results. Connections between variability in ice properties and temperature and
water vapor are explored. The water budget in the upper polar mesosphere is examined using observations
of ice content and water vapor. Comparisons of SOFIE and CIPS results within the common volume will be
discussed.
http://sofie.gats-inc.com
SA43A-1578
Direct Observation of micrometeor differential ablation: Insights into the evaporation of the meteoroid chemical constituents and their relation to ice particles.
Meteoric smoke is believed to provide a major source of condensation nuclei (CN) for the formation of ice particles in the Mesosphere and Lower Thermosphere (MLT). Smoke particles may therefore be a necessary precursor to the formation of noctilucent clouds (NLC) and polar mesospheric summer echoes (PMSE). The smoke forms from the condensation of meteoric material ablated from the billions of extraterrestrial particles entering our atmosphere every day. However, it is not clear, from all the chemical constituents evaporated from the meteoroid, which is the best candidate for the formation of smoke. This makes the accurate understanding of the meteoroid ablation process a crucial step towards the complete elucidation of the microphysics of ice layers. We present the first direct observation of meteoroid differential ablation, providing evidence that this is the main mechanism through which micron-sized particles deposit their mass in the MLT. These results are obtained utilizing two state-of-the-art models to correlate temporal behavior in the received signal of observed radar meteor head-echoes with the precise moment at which a particular chemical constituent is predicted to evaporate from the main body. Prior to this work, differential ablation was merely a hypothesis and there was no known mechanism for remote sensing the individual chemical constituents of meteors so small that they create no measurable light. The coupling of a differential ablation model with an astronomical model of the meteoric flux, combined with large aperture radar observations, will therefore enable the origins of meteoroids within the solar system to be related to the deposition of their constituents in the upper atmosphere, and shed new light on their aeronomical impacts.
SA43A-1579
A Study of Meteoric Smoke Parameters Derived From Arecibo D-region ISR Spectra in Different Seasons
In this work we present a seasonal study of the presence and characteristics of meteoric smoke particles (MSPs) in the D-region plasma derived from observations using the 430 MHz dual-beam Arecibo Observatory (AO) incoherent scatter radar (ISR) in Puerto Rico (18° N, 67° W). MSPs are believed to be the major source of condensation nuclei for the formation of ice particles, the precursor for Polar Mesospheric Clouds (PMCs). Our results are obtained by utilizing a method similar to one developed by Strelnikova et al. [2007, Meteor smoke particle properties derived from Arecibo incoherent scatter radar observations, GRL (35)15] who fitted a summed Lorentzian function to the ISR power spectra in order to derive the MSP sizes and number densities. This method allows us to determine mean particle radii and densities in the 80 – 95 km altitude range during the hours of 10 - 14 AO LT when the detected signal-to-noise (SNR) from the D-region is strongest. Our results provide insight into the presence and distribution of positively charged meteoric dust in the mesosphere resulting from the condensation of ablated meteoric material. Furthermore, we investigate the existence of any correlation between the seasonal variations of the derived MSPs properties with that of the meteoric input function (MIF) in the MLT above Arecibo.
SA43A-1580
Mass Analysis of Charged Aerosol Particles During the MASS/ECOMA Campaign
Abstract. The Mesospheric Aerosol Sampling Spectrometer (MASS) instrument was launched on two sounding rockets in August 2007 from Andoya, Norway to find the masses of charged aerosol particles in the polar mesosphere in NLC/PMSE conditions (3 August) and PMSE conditions alone (6 August). We compare and contrast the four data sets from the uplegs and downlegs. The MASS instrument collected ions, cluster ions, and charged nanometer-sized particles on four pairs of electrically-biased graphite plates that collect positive and negative particles separately. Electron collection was prevented by the negative potential on the rocket body. For the 3 August upleg, the data show charged particle collection on all channels with number densities of order several thousand per cubic centimeter in the four size ranges < 0.5 nm, 0.5-1 nm, 1-2 nm, and > 3 nm. The occurrence of positively charged aerosol particles in the smallest sizes suggests positive ions as the nucleation sites because the smallest particles have negligible probability of charging by photoionization. The signals were smaller on the 3 August downleg as a consequence of the spatial variability of the cloud. For the 6 August upleg into PMSE alone, only smaller particles (< 2 nm) were detected and these were both positive and negative with number densities of several thousand per cubic centimeter. On the downleg, 1-2 nm negatively charged particles were detected, but there were no positive particles in this mass range.
SA43A-1581
The Cosmic Dust Experiment of AIM
The Cosmic Dust Experiment (CDE) onboard the Aeronomy of Ice in the Mesosphere (AIM) mission is a dust impact experiment designed to monitor the variability of the cosmic dust in ux. The instrument consists of fourteen permanently polarized thin plastic film sensors that generate an electrical signal when an impacting dust particle penetrates them. The total surface area is about 0.1 square meters and the detection threshold is about a micron in particle radius. The variability of these small grains is assumed to follow the variability of the dominant 100 micron radius particles, hence the measured flux can be used in correlation studies with various Noctilucent Cloud (NLC) activity indexes. CDE has been observing the cosmic dust influx since June 2007. In this talk, we present the first nine months of reduced data, focusing on the observed temporal and spatial variability of the dust influx. Data collected after February 2008 show increased levels of background noise and preliminary work on reducing this data will also be presented.
SA43A-1582
Electric field measurements in an NLC/PMSE region during the MASS/ECOMA campaign
Multiple high-impedance electric field probes were flown from Norway in August 2007 on each of the two MASS rockets, which were launched through NLC and PMSE events. Within the cloud layer, the probe potentials relative to the rocket skin were driven negative by incident heavy charged aerosols. In the first flight, the amplitude of voltage spikes caused by probe shadowing were large, and followed a profile similar to the probe potential and heavy charged aerosol density. The relationship between the shadowing spike amplitudes and heavy charged aerosol density is used to infer ion conductivity within the cloud layer.