SA21A-0247
Can Charged Dust Explain Polar Mesospheric Summer Echoes? Theory and Experiments
Simultaneous and collocated measurements of Polar Mesospheric Summer Echoes (PMSE) and electron density in the D- and E-regions of the ionosphere with the EISCAT radars have allowed to make accurate absolute calibrations of the PMSE scattering cross sections at 224 MHz (Bragg wavelength of 67 cm) and at 930 MHz (Bragg wavelength of 16 cm). These measurements give volume scattering cross sections of 5250×10-18\ and\ 3.5×10-18 m-1 for the VHF and UHF radars respectively. These unprecedented measurements allow to make a crucial test to the theory of PMSE that asserts that electron turbulence induced by neutral air turbulence can be maintained at the necessary scale lengths by an extension of the Kolmogorov spectrum due to the presence of charged nanometer size ice dust particles which cause an enhancement of the Schmidt number. Using a model of of the Kolmogorov spectrum proposed by Hill that incorporates the Schmidt number, it has been possible to fit to the model the Schmidt number and the dissipation rate of electron density variance, given the two measurements of the volume scattering cross sections. Assuming the most favorable theoretical initial condition, namely that the slow diffusion mode completely dominates the dissipation of electron density variance, Schmidt numbers of a few thousands are possible with low charge numbers; or equivalently, dust radii up to a few tens of nanometers can sustain the required Schmidt numbers. However, it is argued that the assumed most favorable condition is not prevalent in nature.
SA21A-0248
Electric Field Probe Measurements in NLC and PMSE during the MASS rocket Campaign
Electric field and potential perturbation measurements were successfully conducted during two rocket flights from Andoya, Norway in August 2007. The MASS rockets were launched through small to moderate noctilucent cloud and polar mesospheric summer echo events. The identical electric field instruments on each of the MASS rockets included two pairs of booms, forward and aft in the same plane, with two high impedance probes on each boom for a total of eight probes per rocket. Double Langmuir probe measurements were made between all pairs of probes, and involved probe separations from 0.65m to 3.0m both perpendicular and parallel to the rocket axis. After deployment, and below the NLC the electric field probes detected the expected VxB electric field in the rocket frame of reference. Initial analysis indicates that significant voltage perturbations were detected on the first flight during a separated, lower NLC layer, and during a larger, higher altitude PMSE layer. The second flight found similar perturbations during encounter with a PMSE layer. During the PMSE traversal of flight 1 it appears that the rocket became positively charged by about one Volt relative to the external probes, coincident with the aerosol particles.
SA21A-0249
VLF and transient electric fields in NLC and PMSE
Two rocket payloads were launched in August 2007 to study noctilucent cloud (NLC) and polar mesospheric summer echo (PMSE) conditions from Andøya, Norway. The payloads carried a set of instruments to measure the electric field, fluctuations and the distribution of nanometer sized charged aerosol particles. The electric field measurements were performed by two pairs of electric field booms supporting two high impedance spherical probes each. Electric field variations, on the order of tens of millivolts, are seen coincident with the detection of charged particles and the observation of the NLC and PMSE events. The electric field fluctuations extend up to 1~kHz in frequency. The measurements are used to test the atmospheric turbulence origin of PMSE events.
SA21A-0250
A Rocket-borne Ion Mass Spectrometer for the Mesosphere That is Pumped by Rocket Aerodynamics
Rocket-borne mass spectrometers for ions have been flown that were evacuated by cryogenic vacuum pumps with liquid helium or neon. There have not been flights since 1993 because these instruments required expensive deliveries of cryogens and frequent refillings. Advances in (1) aerodynamic modeling, (2) mass spectrometer design, and (3) ion detection technology make possible a new approach to mass spectrometry in the mesosphere in which the spectrometer is pumped by the flow around the rocket. First, the Direct Simulation Monte-Carlo method has been applied to simulating the air flow around the rocket payload. We find that if the forward deck of the payload is supported on a stalk of smaller diameter (10 cm for example), that a low-density void is created below the forward deck by the flow around the payload, assuming that the payload is pointed in the ram direction. The air density below the deck is reduced from ambient by a factor 7 and 15 at altitudes of 80 and 90 km, respectively. The mass spectrometer is exhausted into this void which acts as a pump. In a conservative scenario, the spectrometer is kept evacuated on the upleg then opened at the apogee both at the inlet and exit. Data are acquired on the downleg to 70 km, below which the pressure in the low-density void becomes too high. Second, we use the rotating field mass spectrometer which operates at higher pressure (up to 30 mTorr) than the quadrupole spectrometer because the ion path length is shorter (2 cm) and because a larger ion acceleration potential is used that reduces the ion-neutral collision cross section. Third, we use a new design of channel electron multiplier that has been shown to operate at pressures up to 10 mTorr in the lab, corresponding to the number density at approximately 80 km in the arctic winter.
SA21A-0251
Mesospheric Aerosol Sampling Spectrometer
An instrument has been developed to detect charged, sub-visible aerosol particles in the polar mesosphere. Two of these instruments were launched in August, 2007 from Andoya, Norway as part of the Mesospheric Aerosol Sampling Spectrometer (MASS) campaign and both detected charged aerosols. These in-situ measurements coincided with measurements by the Aeronomy of Ice in the Mesosphere (AIM) satellite and the German/Norwegian Existence and Charge state Of Meteoric dust grains in the middle Atmosphere (ECOMA) rocket campaign. This instrument has a 25 square centimeter entrance slit that admits a continuous flow of air. Venting ports are placed lower on the detector in order to reduce pressure buildup. The air sample flows between three pairs of graphite electrodes biased symmetrically with increasing bias potentials. Electrons, light ions, cluster ions and heavy charged aerosol particles of both polarities are collected mass-selectively on the electrodes that are connected to sensitive electrometers. Direct Simulation Monte Carlo (DSMC) codes have been used to optimize the supersonic airflow within and around the instrument. The calibration of the MASS instrument as well as preliminary results will be shown. Acknowledgement: This project is supported by NASA.
SA21A-0252
Mass-analysis of Charged Aerosol Particles in a PMSE/NLC Layer by a Rocket-borne Spectrometer
The first of two "MASS" (Mesospheric Aerosol Sampling Spectrometer) rockets was launched from the Andoya Rocket Range at 22:51 UTC on 3 August 2007 into PMSE and NLC approximately 26 minutes after an AIM satellite overpass. The sun was 4 degrees below the horizon and the local riometer indicated that the ionospheric conditions were rather quiet, i.e., day time conditions as far as negative cluster ions are concerned. NLC were seen in the previous hour at 83 km by the ALOMAR RMR lidar pointed along the rocket trajectory and were detected at the same altitude by rocket-borne photometer measurements. The rocket carried an electrostatic mass analyzer for the charged fraction of the aerosol particles and both forward and aft deployable electric field booms. The mass analyzer was mounted on the tip of the payload and pointed in the ram direction. It has a forward inlet slit with area of 25 square centimeters and side vents for air exit. Aerosol particles with different ranges of charge-to-mass ratio are collected within the instrument housing on two sets of four biased collector plates, with one set for positive particles and one set for negative particles. A preliminary analysis of the data shows the density of negative particles with radius greater than 3 nm rising sharply at 83 and continuing to 89 km, collocated with PMSE detected by the ALWIN radar. Particles with 1-2 nm radii with both signs of charge and positive particles with less than1 nm radius were detected at 86-88 km. Initial charge-density estimates are several thousands per cubic centimeter for each of these size ranges. The E field booms detected significant potential variations in the PMSE/NLC region. Further analysis will examine in more detail the effects of aerodynamics, payload charging, and spurious charge generation by particle impacts. http://plasma.colorado.edu
SA21A-0253
Comparison of PMC measurements from AIM and SBUV/2
The Aeronomy of Ice in the Mesosphere (AIM) spacecraft, launched on April 25 from Vandenberg Air Force Base, is a satellite mission that explores Polar Mesospheric Clouds (PMCs) in order to find out why they form and why they are changing. Results of this mission will provide new knowledge about the connection between PMCs and the meteorology of the polar mesosphere. The Cloud Imaging and Particle Size (CIPS) instrument is a nadir- viewing instrument from which PMC frequency and brightness can be inferred. It produces panoramic images of scattered radiation at 265 nm with a field of view of 1800 x 800 km and high spatial resolution. This work provides a first comparison of CIPS PMC morphology to concurrent results from the Solar Backscatter Ultraviolet (SBUV/2) instrument, which has provided a 28-year climatology of PMC brightness and frequency. CIPS and SBUV/2 PMC detections are compared for selected days in the 2007 northern hemispheric season. To facilitate comparison, the CIPS footprint of 1x2 km is binned to match the SBUV/2 footprint of 150x150 km at the PMC altitude of 80 km. Because CIPS measures only one wavelength at 265 nm, the SBUV PMC detection algorithm, which normally uses data at five wavelengths between 252-292 nm, is simplified to an algorithm applying just one wavelength. It will be shown that the single wavelength SBUV/2 algorithm gives similar results to the original algorithm. PMC frequency and brightness derived from both CIPS and SBUV/2 using the common algorithm will be compared. Cloud brightness for all latitudes agrees to within 1 percent over the season. In addition, a coincidence analysis of CIPS and all three operational SBUV/2 instruments for the summer 2007 season will be shown.
SA21A-0254
Observation of Ozone Column Densities by the Cloud Imaging and Particle Size Experiment on the Aeronomy of Ice in the Mesosphere 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. The spatial resolution of CIPS observations is 2x1 km in the nadir. The goal of CIPS is to observe Polar Mesospheric Clouds (PMCs) and determine their absolute albedo and particle size distribution. When PMCs are not present, CIPS observes only the sunlit Rayleigh-scattered background brightness, which is controlled by the column ozone abundance above 40 km. These observations are made over a range of scattering angles from 35 to 150 degrees. Following the technique developed for the Solar Backscattered UltraViolet (SBUV) instruments by McPeter's et al. [1980], the ozone column density and the ratio of the ozone and air scale heights may be determined by CIPS observations. We have applied that technique to non-PMC observations by CIPS. We compare CIPS ozone results to historical and current observations, including those of SBUV.
SA21A-0255
High Latitude Dynamics Measured by the Cloud Imaging and Particle Size (CIPS) Experiment on the AIM Spacecraft
The large field of view of Cloud Imaging and Particle Size (CIPS) experiment on the Aeronomy of Ice in the Mesosphere (AIM) mission allows images of the same region of space to be recorded on several consecutive orbits. These data are used to determine the absolute positions of features in the cloud scenes. From consecutive, orbit to orbit images of the same features, atmospheric transport velocities can be determined with an approximately 96 minute cadence set by the orbital period. We will show several examples and discuss the issues and uncertainties involved in the analysis.
SA21A-0256
Common Volume Measurements of Polar Mesospheric Clouds from AIM: Characterization of particle size distribution from CIPS and SOFIE experiments
A prime mode of observation of the Aeronomy of Ice in the Mesosphere (AIM) mission is to make a variety of angular and multi-spectral measurements of PMC in the region of the terminator, where both CIPS (Cloud Imaging and Particle Size Spectrometer) and SOFIE (Solar Occultation for Ice Experiment) observe the same volume of space, separated by about 6 minutes in time. CIPS observes the same volume at a pixel size of 5 km for 7 separate scattering angles, thereby obtaining both the brightness (UV albedo) and scattering phase function. SOFIE observes the same volume at the limb in solar occultation at over a range of near-IR and UV wavelengths. Thus the combination of multi-spectral extinction, and UV scattering at multiple angles place unprecedented constraints on particle size distributions in PMC. We present the first results (northern summer, 2007) for the size and shape of mesospheric ice particles for some case studies from CIPS/SOFIE common volume measurements.
SA21A-0257
The Variability of Cosmic Dust Influx as Seen by the AIM Satellite
The Cosmic Dust Experiment (CDE) onboard the Aeronomy of Ice in the Mesosphere (AIM) mission is a dust impact experiment to monitor the variability of the cosmic dust influx. It is based on 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 (NLC) activity indexes. In this talk we will describe the CDE instrument. We will discuss our challenges in identifying the various noise sources that could possibly contaminate our science measurements, and also our initial science results about the spatial and temporal variability of dust fluxes entering our atmosphere. The results will be compared with expectations based on models, earlier in situ dust measurements, and radar observations. http://lasp.colorado.edu/aim/
SA21A-0258
AIM Receiver/Communication Lock Analysis; When Bad Space Weather is Good
The AIM (Aeronomy of Ice in the Mesosphere) spacecraft (a NASA Small Explorer satellite) was launched on 25 April 2007. Some days after launch, AIM began to exhibit a problem in which it would not always achieve proper receiver uplink communications 'lock'. During several periods in May – August 2007, the solar wind became very quiet and geomagnetic activity went to very low levels. During such times, there were several complete days without successful unlink from the ground operators to AIM. In this context, the Forecast Modeling team of the Center for Integrated Space Weather Modeling (CISM) used modeling tools to examine solar conditions and issued forecasts about geomagnetic activity. This was based on the hypothesis that higher solar wind speeds would lead to greater geomagnetic activity – and this, in turn, would improve AIM operations. Such forecasts have proven accurate: An increase in solar wind and geomagnetic activity often leads to a dramatic improvement in AIM communication uplink. We conclude that the AIM spacecraft receiver lock problem is related to space environment conditions. We have speculated that increased space weather activity helps drive the AIM receiver circuits toward a better operational state. The best predicator of 'good lock' state is a shift from low (or quiet) geomagnetic and solar wind conditions to more disturbed conditions. We have used the CISM Forecast Model tools to predict when propitious conditions should occur. We do not fully understand the mechanism(s) by which disturbed space weather improves AIM performance, but use of CISM tools has been an important, supportive adjunct to a key new NASA flight program which is now operating quite successfully and returning excellent, continuous data.
SA21A-0259
Six Years of NLC Analysis from the Odin Satellite
The Optical Spectrograph and InfraRed Imager System (OSIRIS) onboard the Odin satellite observes noctilucent clouds in the limb at wavelengths between 280 and 800 nm. Since Odin's launch in 2001, mesospheric observation schemes have successively been extended. Today, Odin performs daily limb measurements between 10 and 110 km during the NLC seasons, covering latitudes up to 82° in the north and all the way to the pole in the south. Based on these observations we provide seasonal and latitudinal climatologies of NLCs between 2002 and 2007. From 2 weeks before until 6 weeks after summer solstice a more or less continuous cloud cover is found above 75° latitude. NLC brightnesses increase generally towards higher latitudes. NLCs in the northern hemisphere tend to be brighter than in the southern hemisphere. From the spectral analysis of the OSIRIS data, we derive an effective optical radius as a measure for NLC particle sizes. This effective radius provides a robust parameter for climatological studies of NLC properties as it is less dependent on instrumental and viewing conditions than the cloud brightness. Our analysis shows smaller particle sizes in the southern hemisphere for most seasons. We suggest that the smaller radii and the weaker cloud brightness in the southern hemisphere result from the higher planetary wave activity in the NH winter stratosphere via an interhemispheric coupling. The Odin mission is currently scheduled to continue at least until 2008, as a third party mission within the ESA Earthnet programme, thus providing excellent opportunities for joint mesospheric studies with the AIM satellite.
SA21A-0260
Odin/OSIRIS PMC properties in 2007 in context with the AIM observations
The Optical Spectrograph and InfraRed Imager System (OSIRIS) instrument on the Odin satellite has observed Polar Mesospheric Clouds (PMCs) in both hemispheres since November, 2001. OSIRIS measures the limb- scattered solar radiance between 280 and 810 nm with ~1 nm resolution and this allows PMC particle size retrievals from the UV spectra at 290-305. The sensitivity of the limb-scattering technique employed by OSIRIS and high instrument's signal-to-noise ratio at PMC altitudes also permits the detection of clouds that are only 20% brighter than the corresponding Rayleigh background. This presents a unique opportunity to study PMCs at middle and low latitudes. In this work, PMC properties measured by OSIRIS in 2007 are presented in context with the AIM mesospheric observations during the same time period. OSIRIS PMC occurrence, brightness, altitudes, and particles sizes are analysed in the same latitude region as AIM measurements and also compared to the same parameters measured at other latitudes for different seasons in the northern and southern hemisphere.
SA21A-0261
The Diurnal and Seasonal Variation of PMCs Near 55° N Observed by SHIMMER and CIPS: Implications to Long Term PMC Trends
The Spatial Heterodyne Imager for Mesospheric Radicals (SHIMMER) is designed to measure OH solar resonance fluorescence near 309 nm by imaging the Earth's limb. It has been observing OH and PMCs up to about 58° N since March 16, 2007 from the STPSat-1 satellite. SHIMMER has a local time precession of ~30 min/day so that during the 2007 northern hemisphere summer it observed the entire OH and PMC diurnal cycle. SHIMMER observed hundreds of PMCs in 2007 between 50-58° N. These data complement the PMC data from NASA's Aeronomy of Ice in the Mesosphere (AIM) mission, which are made near local noon. We will compare the SHIMMER PMC frequencies at local noon to those from the Cloud Imaging and Particle Size (CIPS) instrument on AIM. Using the seasonal PMC dependence observed by CIPS, we will infer the local time dependence on PMC frequency for the 2007 NH summer from the SHIMMER observations. We will then consider the implications to long term PMC trends as applied to satellite observations that vary slowly in local time from year to year.
SA21A-0262
Ozone Gravitywave Observations from the AIM Satellite
The CIPS (Cloud Imaging and Particle Size) instrument aboard the newly launched AIM (Aeronomy of Ice in the Mesosphere) satellite has been analyzed for the presence of gravity waves in the observed albedo. AIM is in a sun synchronous orbit with an equatorial local time currently centered near noon. CIPS is a nadir viewing CCD imager with a field of view of approximately 2000 km along track and 1000 km across track. The pixel size at nadir is 2 km by 1 km. CIPS observes albedo at 265 nm. At this wavelength and in the absence of PMCs (Polar Mesospheric Clouds), variations in ozone densities in the 40 to 70 km altitude region dominate the deviations in albedo which would be expected from an unchanging atmosphere across the field of view. Under the assumption that ozone is the sole driver for the albedo structure observed, high resolution 2D ozone structure has been inferred from the images. Initial analysis has indicated that the principle scale of ozone structure is typically on the order of 1000km. Typical amplitudes are on the order of 2% (4% peak to trough) in ozone density.
SA21A-0263
Gravity wave observation from the Cloud Imaging and Particle Size (CIPS) Experiment on the Aeronomy of Ice in the Mesosphere (AIM) Spacecraft
The Cloud Imaging and Particle Size (CIPS) experiment is one of the three instruments on board the Aeronomy of Ice in the Mesosphere (AIM) spacecraft that was launched into sun-synchronous orbit on April 25, 2007. CIPS is a 4 camera wide-field (120° x 80°) imager designed to measure PMC morphology and particle properties and has a spatial resolution of 1 x 2 km in the nadir. Structures observed in PMC's occurring near the cold summer mesopause have been attributed to various wave and instability processes and it has been suggested that PMC structures may be used to infer quantitative properties of gravity wave activity. One of the objectives of AIM is to investigate gravity wave effects on PMC formation and evolution. CIPS images show distinct wave patterns and structures in PMC's. In this work, we present initial analysis of the gravity wave structures observed in PMC's near 80-85 km altitude. Wavelengths of structures seen in PMC's range between 15 - 300 km, with smaller wavelength structures of less than 80 km being most common. We also present wave structures observed from the Rayleigh scatter background albedo at 50 km altitude at low latitudes and from PMC free orbits. The wavelength of structures observed from the background albedo show an equal distribution between 150 – 400 km. A comparison of the wave structures at the two altitudes will be made to determine differences in the observed wave parameters. We will also investigate the seasonal and latitudinal variations in the nature of the waves observed.
SA21A-0264
Multi-Instrument Measurements of Noctilucent Clouds in Coordination with the AIM Satellite
With the recent launch of the NASA Aeronomy of Ice in the Mesosphere (AIM) satellite in April 2007 the opportunity exists to perform novel coordinated satellite and ground-based measurements of noctilucent clouds (NLC), to better quantify their nature, temporal development, latitudinal extent and longitudinal variability. These measurements will also help shed new light on the long-standing question on the differences (if any) between NLC, which are naturally limited in their observation to latitude ranges of typically 50-65°, and Polar Mesospheric Clouds (PMC) as detected at higher latitudes during the summer months from space borne instruments. Here we present new two-station image measurements of NLC from Edmonton, Canada (53° N) recorder during July 2007, providing detailed information on the cloud dynamics near their equatorward edge, for comparison with the UV cloud signatures as determined by the Cloud Imaging and Particle Size (CIPS) instrument on the AIM satellite. These results are then contrasted with high-latitude (65°N) cloud measurements using AIM in coordination with multi-station imager, lidar and radar observations of Polar Mesospheric Summer Echoes (PMSE) using the new PFISR system at Poker Flat, Alaska.
SA21A-0265
Large-scale Dynamics of Noctilucent Clouds Over Alaska, 2005
Noctilucent clouds (NLC) form in the coldest region that exist on Earth, near the polar summer mesopause at an altitude of approximately 83 km. Coincident ground-based observations of NLC were made from interior Alaska over a 3-day period in August, 2005, using imagers and lidar. The imagers were deployed at Donnelly Dome (63° N, 145° W) approximately 175 km south of the lidar facility. The observed NLC displays were unusually extensive considering the late season, filling the twilight sky from horizon-to-horizon and lasting >4 hours. In particular, the night of August 10 showed a remarkable display extending well south of the observation site (> 125° elevation). Recent modeling results (Berger and von Zahn, 2007) showed how meridional winds can transport the icy particles southward from their nucleation site. Co-located MF radar data support this suggestion. We compare these data with simulations by the NRL Navy Operational Global Atmospheric Prediction System- Advanced Level Physics and High Altitude (NOGAPS-ALPHA) as well as with published work by Berger and von Zahn, 2007.
SA21A-0266
Lidar Observations of Polar Mesospheric Clouds in Conjunction with an AIM Overflight
On August 10, 2007 a dramatic polar mesospheric cloud display was observed visually and by a lidar system from the Sondrestrom Upper Atmosphere Research Facility near Kangerlussaq, Greenland (67.0N, 309.1E). The PMC was detected in the lidar's vertical beam from approximately 01:30 UT until local sunrise near 07:30 UT. The AIM spacecraft passed within a few hundred kilometers of the site near 02:20 UT, placing the site well within the viewing angle of the CIPS instrument. The SOFIE instrument on AIM made measurements within 700 km of the lidar observations. The lidar detection indicates typical PMC characteristics with an altitude near 82 km, a thickness of 1 km and a backscatter coefficient near 100. The CIPS images will place in context the lidar observations and the CIPS measurements of the scattering phase function will help constrain PMC particle size. The SOFIE measurements will help determine the temperature and water vapor conditions in the region of the lidar observations. The detailed lidar measurements complement the satellite observations and provide for the first time a detailed view of a PMC simultaneously from ground and space.
SA21A-0267
Seasonal variations of mesospheric Fe layers at Rothera and comparisons to the South Pole results
Based on two and half years of lidar observations made by the British Antarctic Survey and the University of Illinois at Rothera (67.5S, 68.0W), Antarctica with an Fe Boltzmann temperature lidar, a systematic analysis was made to characterize the mesospheric Fe layers at this high southern latitude. Rothera Fe layer characteristics are then compared to the South Pole results reported earlier. Rothera seasonal variations of Fe layers share some similar features as those of the South Pole but there are distinct differences between these two sites. Among them, the summer Fe layers at Rothera have lower peak altitude but much high abundance than those of the South Pole. This may be attributed to the heterogeneous removal process by the apparent different occurrence frequencies of polar mesospheric clouds (PMC). Meanwhile, the midwinter Fe layers at Rothera show very low peak altitude (~80 km) and sharp bottom edge. We will seek the explanations for the results through comparison to a mesospheric Fe chemistry model.
SA21A-0268
Seasonal variations of stratospheric gravity waves in Antarctica and correlations to polar mesospheric cloud brightness in summer
Gravity waves (GWs) play an important role in the dynamics of global middle and upper atmosphere. However, quantitative characterization of GWs in the upper stratosphere is still rare in Antarctica. Here we present a study of stratospheric GW parameters and seasonal variations using the data obtained with the University of Illinois Fe Boltzmann/Rayleigh lidar at the South Pole (90°S) from December 1999 to January 2001 and at Rothera (67.5°S, 68.0°W) from December 2002 to March 2005. Through analyzing the Rayleigh lidar density data in 30-60 km, GW parameters are derived for the South Pole and Rothera, and the results are comparable. The annual mean GW vertical wavelength is 4.3 +/- 1.5 km, vertical phase speed is 0.33 +/- 0.15 m/s, and the period is 245 +/- 110 min. We characterize the stratospheric GW strength with the root- mean-square (RMS) relative density perturbation. The seasonal variation of GW strength is clear at Rothera, with the maximum in winter and the minimum in summer. No significant seasonal variations are observed at the South Pole. The data also show that the GW period is shorter in summer than in winter at Rothera. In addition, the stratospheric GW strength is negatively correlated with PMC brightness at Rothera but no significant correlation at the South Pole. Two important factors, i.e., the wind filtering effect and topographical GW source difference, are investigated in order to explain the GW seasonal variations. We then apply a GW ray-tracing model to analyze the GW source and propagation. The correlation between GW strength and PMC brightness also provides a clue of GW propagation from the stratosphere to the mesosphere.
SA21A-0269
What can we Learn From Ground-based Photography of Noctilucent Clouds?
Since the summer 2004, photographs of noctilucent clouds (NLC) are taken from the top floor window of the Arrhenius Laboratory at the University Campus 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. Time-lapse movies, which magnificently visualise dynamical character of the mesopause region, can be made out of these image series. Wave-like structures of different spatial scales, non-periodic features of different shapes and sizes and front-like structures can usually be observed as they move through the twilight arch. The images have, however, to be re-projected to a horizontal plane in order to correctly represent movements and actual spatial scales. A study of such images provides tools for analyzing the dynamics of this region of the atmosphere. In fact, NLCs work as a tracer of the coherent structures forming or propagating at the mesopause level. Optical studies of similar phenomena have already been conducted using the mesopause region airglow emissions as markers of the waves. Since an NLC layer is significantly thinner than a typical airglow layer (2-3 km compared to 8-9 km) the observed wave signatures should appear much more distinct (or "sharp") in NLCs and thus could be studied in much better detail. Analysis of such still images and time-lapse movies provides information on the region's dominating wind (bulk motion) and characteristics (wavelengths, phase velocities) of periodic features. Examples of such investigation will be presented. http://www.misu.su.se/~jacek/nlcmovies.html
SA21A-0270
Studies of Noctilucent Clouds With an Inter-Continental Network of Automatic Digital Cameras
Noctilucent clouds (NLC) are the highest clouds in the Earth's atmosphere, occurring around the mesopause at 80-85 km altitudes. They can be seen during summer nights (May-September in the northern hemisphere). These clouds are composed of small ice particles scattering sunlight, making NLC readily visible against the dark twilight sky. NLC are excellent indicators of the physical state of the mesosphere and may be readily studied with ground- based instruments. The presence (or absence) of NLC is determined by the complex combination of a number of characteristics of the mesosphere: temperature, abundance of water vapor, meteor dust particles and hydrated ions. NLC are not uniformly distributed in the mesosphere around the globe, but some processes control their spatial and temporal variability. A ground-based network of digital cameras is an excellent tool to monitor NLC formation and dynamics around the globe as well as to study the wind regime and wave activity in the mesosphere. Since 2004, automatic digital cameras have been operating during summer time (May 25 - August 15) to register NLC. In 2007 the five cameras were in Athabasca (Canada), Port Glasgow (Scotland), Aarhus (Denmark), Moscow (Russia), and Novosibirsk (Russia). These points have near the same latitudes (between 55N and 57N) and are separated by a long distance in longitude. This provides comparable NLC observations in the same latitude circle and allows studying NLC homogeneity on continental scales as well as gravity and planetary wave activity. The combination of NLC observations made from ground and space will provide us valuable information on the NLC geographical distribution and atmospheric processes taking place in the mesosphere during the NLC season.
SA21A-0271
Measurements of Meteor Smoke and Ice Particles During the ECOMA-2006 and ECOMA/MASS-2007 Rocket Campaigns
In the course of the European ECOMA project (ECOMA = Existence and Charge State of Meteoric Smoke Particles in the Middle Atmosphere) two sounding rocket campaigns were conducted in September 2006 and August 2007 from the North Norwegian Andoya Rocket Range (69N). The latter campaign was closely coordinated with the US-American MASS campaign which also focused on mesospheric aerosol particles and their plasma environment. A core instrument of the ECOMA payload is a Faraday-Cup-based particle detector which is combined with a Xenon-flashlight for the active photo-ionization of mesospheric aerosol particles. The first launch in September 2006 revealed evidence for meteor smoke particles in the entire altitude range from 60 - 110 km, as indicated by detected photo-emission signatures. In August 2007, however, when the ECOMA payload was launched into a weak event of polar mesosphere summer echoes and noctilucent clouds, particle signatures were confined to the altitude region of mesospheric ice layers identified by the ALWIN MST radar and the ALOMAR RMR lidar, i.e., roughly between 82 - 88 km altitude. These results will be discussed in the scope of our current understanding of the seasonal distribution of meteor smoke particles, corresponding implications for the nucleation of mesospheric ice clouds, and the physical mechanisms giving rise to polar mesosphere summer echoes.
SA21A-0272
Reduced meteoric smoke particle density at the summer pole - implications for mesospheric ice particle nucleation
Noctilucent clouds (NLC) and polar mesospheric summer echoes (PMSE) are phenomena that occur in the summertime polar regions due to the presence of ice particles around the mesopause. That ice particles are able to form in a region with such low water vapor concentration as the mesopause is noteworthy. Even though the summer mesopause is the coldest region on earth, temperatures are generally not low enough for homogeneous nucleation to occur, which necessitates the presence of pre-existing condensation nuclei. The nature of these nuclei has long puzzled the scientific community and many candidates have been suggested, such as particles of meteoric origin, ion clusters, sodium bi-carbonate, sulfate aerosols and soot particles. Out of these the so called "smoke particles", i. e. particles re-condensed from ablated meteoritic material, have long been considered the most likely. Generally, it has been believed that these particles exist in numbers of the order of thousands per cubic centimeter at the mesopause. This belief is based on 1-dimensional studies of meteoric material. A recent 2-dimensional model study, which includes the atmospheric circulation from summer to winter pole however, suggests much lower number densities at the summer mesopause. We here investigate the implications of low number densities for the formation of ice particles. We find that even though resulting ice particle distribution may produce typical NLC brightness, the number density of ice particles is not consistent with what is expected for NLC and PMSE. In particular, it is much lower than the ice particle concentration (>1000 cm-3) typically expected to explain the "electron bite-outs" that are frequently observed in the vicinity of PMSE's. We therefore re-examine the assumptions and parameters that determine the smoke distribution. We show that even though the number of condensation nuclei at the polar summer mesopause can be increased within the uncertainties, the results in most scenarios remain insufficient. We show that charged particles, perhaps in combination with significant deviations from the mean mesospheric state, may be necessary for condensation of ice particles in the polar summer mesosphere.
SA21A-0273
The importance of charging processes for mesospheric ice nucleation
Meteoric smoke particles are considered the most likely condensation nuclei for ice in the mesosphere. Open nucleation questions concern the number and size distribution of smoke. The critical radius above which neutral smoke can act as condensation nuclei is about 1 nm. Hence, while the smoke population is thought to be dominated by sub-nanometer particles, only larger particles are considered important for ice nucleation. Recent model simulations show that the global circulation efficiently transports meteoric material away from the summer pole, resulting in a shortage of condensation nuclei just at the summer mesopause. This provides a challenge for our current understanding of NLC and PMSE. In this paper we argue that smoke charging is critical for the nucleation of mesospheric ice. As the Gibbs free energy barrier disappears for charged particles at sufficiently low temperatures, charging can remove the 1 nm size threshold of ice nucleation. We show that this is feasible at typical mesospheric temperatures and, hence, that all charged smoke regardless particle size can be turned into condensation nuclei. This in turn has large implications for the number and size distribution of NLC and PMSE ice particles. Of central importance is the question what fraction of meteoric smoke is actually charged. We discuss this in terms of microscopic smoke properties and the charging processes prevailing in the D-region dusty plasma.
SA21A-0274
Microphysical studies of mesospheric sulfate aerosol as PMC nuclei in WACCM3
We present the first three-dimensional calculations of the mesospheric sulfate layer. Since this new class of particles was proposed, it has been suggested as a source of nuclei for polar mesospheric clouds (PMCs). Homogeneous nucleation of water vapor is too slow to account for observed PMC particles, necessitating the existence of nuclei, the character of which is as yet unresolved. The leading candidates are dust particles generated by recondensation in meteor trails, ion nucleation resulting from proton hydrates, and nucleation on sulfate particles generated in situ near the mesopause. However, neither the smoke particles, nor the sulfate aerosols, nor the proton hydrates have been measured directly and unambiguously. Recent modeling studies have raised questions about whether sufficient concentrations of dust particles exist in PMC nucleation regions. 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 altitudes from the Earth's surface to the thermosphere. WACCM3 reproduces well the unique structure of the mesopause region that is critical to this study, comparing well to observations of water vapor and temperature. We have merged WACCM3 with the Community Aerosol and Radiation Model for Atmospheres (CARMA), a bin microphysics model that has been used extensively for simulations of a wide range of aerosol and cloud types, including PMCs and sulfates. Above about 35 km, increasing temperatures evaporate the stratospheric sulfate layer, producing H2SO4 vapor. Although visible light does photolize H2SO4 by vibrational overtone excitation, we calcuate that sufficient H2SO4 survives this weak photolysis to produce sulfate in the cold summer upper mesosphere, where PMCs form. We present calculations of this mesospheric sulfate layer, and discuss its suitability for PMC nucleation. We also discuss the effects of volcanic eruptions on the number of sulfate particles and nucleation sites.