SA41A-1537
Highlights of the CAWSES Global Tidal Campaigns
To date, four CAWSES (Climate and Weather of the Sun Earth System program, a SCOSTEP sponsored program) Global Tidal Campaigns have taken place over the past three years. These, along with several workshops, have provided a forum for the inter-comparison and combination of ground based and satellite observations and models, and covered the four seasons. This work established the equivalence between satellite and meteor radar observations and demonstrated that the reconstructed total tidal fields from satellite analyses must be used for this equivalence. Significant geographical variation in the diurnal and semi-diurnal amplitudes was also demonstrated and shown to vary with season. These comparisons are being extended to include temperature, airglow and constituent signatures. These campaigns have also provided the opportunity to link thermospheric and ionospheric tidal signatures to the neutral signatures from below. Of the four campaigns, the northern hemisphere winter solstice campaign of December/January 2007/2008 has shown the most tidal variability likely because of the strong warmings which took place. Comparisons with models (four GCMs and two mechanistic models) are now taking place and indicate reasonable agreement for some components and disagreement for others. Identifying what improvements are needed before models can duplicate the observed geographical variability in tidal signatures is now under way.
SA41A-1538
Polar Tidal Signatures in the Extended Canadian Middle Atmosphere Model
The polar regions in the mesosphere and lower thermosphere are the site of unique tidal
features. These tides transport and modify the chemistry of constituents throughout this
region. In order to study the transport of the constituents by tidal features in the
region, we need to determine the dominant components of the tides and their vertical
structures and seasonal variations as the first step.
A one-year run of the extended Canadian Middle Atmosphere Model (CMAM) is used to
characterize the tidal signatures in this region. Significant amplitudes from wave 0
through wave 4 appear in the model run. The wind and temperature signatures of the
dominant components of the diurnal semidiurnal and terdiurnal tides are discussed and
their seasonal variations presented. The spatial variations of their superposition are
also calculated. Semidiurnal and terdiurnal (as opposed to diurnal) migrating and
non-migrating tides dominate in the polar region.
http://www.unb.ca/fredericton/science/physics/CAWSES_GTC/
SA41A-1539
Polar cap mesopause dynamics during a calm polar vortex season
Measurements of mesopause region winds are reported using a ground based Michelson interferometer stationed under the Arctic polar cap. Time series of the measurements are analyzed during a relatively calm polar vortex season, in the absence of major stratospheric warming events. Variability of winds is analyzed for tidal, planetary and gravity wave signatures, and compared to the state of the stratospheric vortex derived from assimilated data. The results are interpreted in terms of degree of vertical coupling of the upper stratosphere and the mesopause.
SA41A-1540
Observation of local tidal variability and instability, along with dissipation of diurnal tidal harmonics in the mesopause region over Fort Collins, CO (41°N, 105°W)
During the 9-day continuous campaign in September 2003, the Colorado State University sodium lidar observed significant short-term tidal variability in both diurnal and semidiurnal tides above 85 km in days 265- 268. Both diurnal and semidiurnal amplitudes dramatically increased on day 267 with a continuous phase advance in diurnal tidal harmonics, causing local atmosphere to become dynamically unstable. Following the dynamical instability associated with tides, we observed equally dramatic decrease in diurnal amplitude, which was accompanied by rapid and continuous phase retardation at 87 km on day 268; the accompanying diurnal phase profiles changed from propagating mode to evanescent mode. Since the time scale of the observed variability during days 265-268 is less than one day, gravity wave/tidal interaction at least is partially responsible for the observed variability. The observed changes in tidal amplitudes and phases are correlated with gravity wave activities concurrently observed by an OH all-sky imager at nearby Yucca Ridge station, as suggested by well known models of tidal/gravity wave interactions. The stability analysis in the night of 267, when both diurnal and semidiurnal reached the maximum amplitudes, revealed that the running daily tidal waves alone, superimposed with the associated mean state, are able to push the atmosphere into local dynamical instability near 90-95 km. The eddy diffusion associated with the instability is believed to have caused a strong dissipation of diurnal tide as observed on day 268.
SA41A-1541
Tides observed by Na lidar at Colorado State University and studies of anomalous winter diurnal tide using TIMED/SABER and HAMMONIA
The Na lidar at Colorado State University (40°N, 105°W) has the capability to measure mesopause region (80-110 km) temperature, zonal and meridional winds over full diurnal cycles. By performing harmonic analysis on this unique data set from May 2002 to April 2006, monthly climatologies of diurnal and semidiurnal tidal perturbations have been obtained. Since solar thermal tides are global scale waves, global tidal signatures deduced from satellite observations will greatly extend the spatial coverage beyond that of a single ground-based station. Therefore, results of satellite observations and GCM predictions are expected to provide global perspectives and deeper understanding of tidal behavior deduced from local observations. In this paper, tidal perturbations observed by the CSU Na lidar are compared with reconstructed tides observed by the TIMED/SABER instrument and with HAMMONIA model outputs to elucidate the global context of the nearly-evanescent temperature diurnal tides observed by the CSU Na lidar during the winter solstice period. This anomalous behavior is studied, along with information provided by observations from the TIMED/SABER instrument and HAMMONIA model, to ascertain the possible influence of nonmigrating tides on CSU Na lidar observations during this period.
SA41A-1542
Influence of an Ultra Fast Kelvin Wave on the Migrating Diurnal Tide
The migrating diurnal tide is one of the dominant dynamical features of the Earth's Mesosphere and Lower Thermosphere (MLT) region, particularly at low latitudes. While the long term evolution of the migrating diurnal tide is dependent primarily upon seasonal changes in the solar heating profile and the background atmosphere, short term fluctuations on the order of a few days have been observed, occurring at time scales too short to be explained by changes in solar heating. These short-term fluctuations are often manifested as a modulation of tidal amplitudes at frequencies corresponding to those of propagating planetary wave modes, suggesting that short term variability in the tide can be driven by nonlinear wave-wave interactions between the tide and various propagating planetary waves also present in the region. However, many questions still remain about the nature of such interactions. The conditions under which various planetary waves may or may not interact with the atmospheric tides, as well as the mechanisms and overall effects of a planetary wave / tidal interaction are still unclear. In this study, we explore the effect of ultra fast Kelvin waves (UFKWs) on the migrating diurnal tide. The UFKWs are eastward propagating disturbances that occur sporadically throughout the year in the low latitude MLT region where the migrating diurnal tide is large. The NCAR Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) is used to simulate a control case without a UFKW and cases in which a UFKW of various magnitudes is present. Use of a global circulation model in this way allows us to characterize the effects of UFKW on the migrating diurnal tide and to investigate the underlying physical processes responsible for the interactions. Initial studies have indicated the UFKW does clearly modulate the amplitude of the tidal parameters influencing the overall amplitude and spatial structure of the migrating diurnal tide.
SA41A-1543
Understanding Short Term Variations of the Migrating Diurnal Tide
The upward propagating diurnal tide dominates the wind and temperature structure of the mesosphere and lower thermosphere. This phenomenon is forced in the lower atmosphere due to the absorption of infra-red radiation by water vapor in the troposphere and to a lesser extend the absorption of ultra violet radiation by ozone in the stratosphere. As the migrating diurnal tide propagate vertically, away from the source region, it can be impacted by a number of sources which can modify the amplitude and phase of the diurnal tide. These nonlinear interactions associated with the background zonal mean winds, dissipation and other large scale planetary waves can impact the amplitude and phase structure of the globally coherent migrating diurnal tide. Observations, primarily from ground-based radar and optical systems, have shown that the locally observed 24 hour oscillation, typically associated with the diurnal tide, can vary significantly over time scales from days to months. Satellite observations, which typically require integration times of months to extract the migrating tidal information have also shown the long period seasonal and interannual variations captured by the ground based observations. These long period variations have been replicated in both mechanistic and global circulation models, however the shorter period variations which occur on timescales of days have proven difficult to capture from observations and replicate using numerical models. One area that is problematic in understanding the day-to-day variability of the diurnal tide is the difficulty in separating potential sources of variability from the observations. From the ground-base perspective it is not clear if the observed variability is due to changes in the migrating diurnal tide or changes in other non- migrating components which cannot be separated from the migrating diurnal tide with measurements from multiple stations at similar latitudes. When utilizing measurements from a single satellite the difficulty arises from the fact that while the satellite provides nearly global coverage, all of the measurements on a give day are made at only one or two specific phases of the tide. To resolve this issue measurements are typically made over an extended time interval of months to build up measurements from multiple phases of the tide before inferring the tidal amplitudes. As a result of this process any short term variations in the tide are smoothed out. In this paper we will present an approach for utilizing observations from multiple satellite measurements to determine the global day-to-day variability of the migrating diurnal tide. Observations from the SABER instrument on the TIMED mission and the MLS instrument on the AURA mission will be combined to create estimates of the daily migrating diurnal tidal amplitude and phase. These results will be interpreted in an effort to understand the potential sources of variability associated with the migrating diurnal tide.
SA41A-1544
The effects of the Quasi-Two Day Wave on Airglow observations at Alice Springs and Buckland Park Australia
The Quasi-Two Day Wave (QTDW) is a planetary wave which, although present globally, becomes intense in the southern hemisphere (especially at mid southern latitudes) in January through February. While the effects of the QTDW on the winds has been well documented only a few studies have been made on the effects on airglow emissions (e.g. Ward, W. E., B. H. Solheim, and G. G. Shepherd (1997), Two Day Wave Induced Variations in the Oxygen Green Line Volume Emission Rate: WINDII Observations, Geophys. Res. Lett., 24(9), 1127–1130). Two airglow imagers have been situated in Australia, at Buckland Park (3455S, 13836E) and Alice Springs (2342S, 13353E), since 2001. These instruments obtains images of the OH Meinel (6,2) band (hereinafter OHM) and O2 Atmospheric (0,1) band (hereinafter O2A) band emissions. A sequence of five images is obtained, each at 1 min integration, through separate narrow passband filters. Two of the filters cover two different rotational lines of OHM, two filters cover different portions of O2A, and one filter covers the background and has almost no airglow emission in its passband. The latter is used to correct the airglow images for background skylight. Thus, one can obtain images of the OHM and O2A airglow, the intensity and temperature of the OHM and O2A emissions, and atmospheric gravity wave horizontal wavelengths and velocity. A review of all the data have revealed some interesting phenomena that appear to be related to the presence of the QTDW. These include greatly enhanced airglow intensities, the potential for ducting of atmospheric gravity waves that originate in tropospheric convective sources, and perhaps even the presence of mesospheric bores. In this paper we will review the results of these airglow data with respect to the QTDW.
SA41A-1545
Doppler Ducting Measurements of Short-Period Gravity Waves and Mesospheric Bores in OH and O2 Airglow Emissions
Under special wind conditions short-period gravity waves and bores can be Doppler ducted in a region of vertical propagation bounded by regions of evanescence in the mesosphere and lower thermosphere (80- 100 km). The bore events are characterized by long-lived, sharp bright (or dark) leading fronts that are usually accompanied by a growing number of coherent wave crests. Using simultaneous imaging and background wind measurements from Maui, Hawaii (20.70 N, 156.30 W), during 2003, the ground-relative and intrinsic parameters of ducted short-period waves have been investigated. Here we present two examples of small-scale, short-period gravity wave and bore events observed in the mesospheric OH and O2 airglow emissions. The measurements were obtained using the Utah State University Mesospheric Temperature Mapper (MTM) which sequentially sampled the near-infrared OH and O2 airglow emissions centered at ~87 and ~94 km, respectively, and the University of Illinois meteor radar which provided continuous hourly wind measurements over the altitude range of 80-100 km. Utilizing measurements of the local background wind field, the intrinsic wave parameters and hence the propagation nature of the wave can be investigated. In this paper, we present new evidence for strongly ducted waves and compared their signatures with theoretical Doppler ducting profiles.
SA41A-1546
Numerical modeling of ducted gravity waves: Impacts of multiple gravity wave sources
We present numerical simulations of mesospheric inversion layer-ducted gravity waves in the mesopause as generated by spatially and spectrally varying tropospheric gravity wave sources. Specifically, when multiple gravity wave sources are allowed to generate gravity waves and allowed to propagate into the mesopause, a portion of the resultant gravity wave spectrum is ducted by the artificial mesospheric inversion layer. The resultant ducted wave signature (i.e., that which would be observed by an all-sky imager or photometer) is studied in detail and compared to experimental observations. We find that there are a number of tropospheric sources configurations that can form the signature of a mesospheric front, like a mesospheric bore.
SA41A-1547
Observations of High-Frequency AGW Activity from Na Lidar Measurements
This paper reports a novel technique to observe high-frequency gravity wave activity from Na-lidar measurements. Typically, Na lidar systems are used to observe longer wave periods, atmospheric tides, and other features that have time scales on the order of hours to tens of hours. However, by applying standard signal processing techniques to the Na temperature and density measurements, waves with periods of only a few minutes have been observed. Here, we show the results of this new technique on Na lidar data collected from the Illinois Data Campaign 2007 and compare them to results achieved from correlating the phases of the OH and OI wave variations observed in coincident airglow images. The significance of the method reported in this paper is that it can be immediately applied to existing lidar data in the current studies of atmospheric gravity waves.
SA41A-1548
Recent sounding rocket flights of a mesospheric charged dust detector
Various versions of fairly simple faraday-cup-style mesospheric charged dust detectors have been flown in recent years on mesospheric sounding rockets. The Dartmouth/UNH dust detector, one of the simplest versions, has been flown multiple times as a standalone instrument. This past year we have had the opportunity to fly copies of this instrument on several payloads with more complete instrumentation suites, allowing the comparison of the Dust Detector response both to other particle signatures, and to the response of similar dust sensors. On January 31st 2008, the detector was flown as part of the HotPay2 Campaign fromthe Andøya Rocket Range, Norway. On 30 June 2008 (1322UT) and 12 July 2008 (1046UT), another copy of the detector was flown on the ECOMA-04 and ECOMA-06 flights, also from Andoya. The HotPay2 flight, together with a new and more rigorous model of the detector response, allows a careful comparison of the dust density measurement to the densities of the ambient thermal ion and electron populations. The ECOMA flights allow comparison to both the Univ Tromso (Havnes) dust detector and the IAP (Rapp) dust detector, as all three sensors flew on both ECOMA missions. The data obtained with the Dartmouth/UNH Dust Detector on the HotPay2 flight show a peak charged dust density of approximately 500 particles per cc at 87 km. This interpretation, based on a newer and more rigorous model of the detector response, gives a five-fold increase from the estimated density of previous analyses. The measured HotPay2 ion density and electron density instruments show a net positive plasma charge in the 80-100 km range. By comparing the absolute dust density measurement to the profile of net positive charge, the mesospheric plasma's apparent non- neutrality may be explained by the presence of the observed negative charged dust layer in the 77-97 km altitude range.
SA41A-1549
Large Amplitude Dynamic Events Near the Mesopause Observed in Na Lidar Measured Wind, Temperature, and Density
Large amplitude dynamic events are frequently observed in the 85-105 km altitude region in data from Starfire, NM, Maui, HA, and Urbana, IL. Similar events at Maui have been analyzed by Larsen et al., [2004, J. Geophys. Res., 109, doi:10.1029/2002JF003067] and Hurd et al. [CEDAR poster, Utah, 2008] from Na lidar data. The events have a vertical extent of large temperature anomalies over 4-6 km, with a period of 3- 6 hours. All the events consist of a cold (upwelling) followed by a warm (downwelling) phase. Na density enhancements and depletions above the events as well as the horizontal winds provide insights into the cause for specific events (i.e. Li et al. , 2007, Investigation of a "wall" wave event, J. Geophys. Res., 112, doi10.1029/2006JD007213).
SA41A-1550
Electron Scavenging in the Night-Time Mesosphere - A Collection of Empirical Data
In the nocturnal lower ionosphere there are always more positive ions than electrons and the difference for charge neutrality is generally ascribed to negative ions. The absence of direct sunlight and atomic oxygen allows to describe the relation between electrons, positive and negative ions in a very simple way, essentially only depending on the ratio between attachment rate of electrons to molecules and ion-ion recombination. From 27 sounding rocket flights we find that this ratio scatters by more than two orders of magnitude which can neither be explained by uncertainties of the attachment rate, nor by the ion-ion recombination. The ratio does, however, vary largely as one would intuitively expected as a function of temperature, ionization, solar zenith angle and indeed the phase of the moon. But to explain the huge scatter in the data we suggested that electron scavenging by particles larger than molecules such as meteoric smoke may reconsile the observations.
SA41A-1551
Satellite Investigation of Atmospheric Metal Deposition During Meteor Showers
Using the nadir-viewing Global Ozone Measuring Experiment (GOME) UV/VIS spectrometer on the ERS-2 satellite, we investigate short term variations in the magnesium column densities and any connection to possible enhanced mass deposition during a meteor shower. We derive a time dependent mass flux rate due to meteor showers using published estimates of mass density and activity profiles of meteor showers. An average daily mass flux rate is also calculated and used as a baseline against which calculated shower mass flux rates are compared. These theoretical mass flux rates are then compared with GOME derived metal column densities from the years 1996 - 2001.There appears to be little correlation between theoretical mass flux rates and changes in the Mg and Mg+ metal column densities. A possible explanation for the lack of a shower related increase in metal concentrations may be differences in the mass regimes dominating the average background mass flux and shower mass flux.
SA41A-1552
Seasonal Variation in Meteor Decay Time Profiles Measured by a Meteor Radar at King Sejong Station (62°S, 58°W), Antarctica
A VHF meteor radar at King Sejong Station (62°S, 58°W), Antarctica has been detecting echoes from more than 20,000 meteors per day since March 2007. Meteor echoes are decayed typically within seconds as meteor trail plasma spread away or are neutralized. Assuming that diffusion is the only process for decay of meteor echo signals, the atmospheric temperatures and pressures have been inferred from the measured meteor decay times at the peak meteor altitudes around 90 km. In this study, we analyze altitude profiles of meteor decay times in each month, which clearly show a maximum at 80 ~ 85 km. The maximum appears at higher altitude during austral summer than winter. The fast decay of meteor signals below the maximum cannot be explained by atmospheric diffusion which decreases with increasing atmospheric densities. We find that the measured meteor decay time profiles can be fitted with a loss rate profile, in addition to diffusion, with a peak altitude of 55 ~ 73 km and a peak rate of 4 ~ 15 sec- 1. The additional loss of meteor plasma may be due to electron absorption by icy particles in the mesosphere, but the estimated peak altitudes are much lower than the layers of NLC or PME. The estimated peak loss rates seem to be too large to be accounted by absorption by icy or dust particles. We will discuss other processes to explain the fast meteor times and their variation over season.
SA41A-1553
Characteristics of the Lower Thermosphere and Ionospheric D Region Deduced From High Time-Resolution Sporadic E-Layer Data During the Solar Eclipse of August 1, 2008
The digital ionosonde at Sodankylä Geophysical Observatory, Finland, is performing continuous high time resolution soundings since the beginning of IPY in 2007. During the partial solar eclipse which occurred on first of August, 2008, a stable sporadic E layer was observed with the ionosonde. Using the time development of the recorded echo power of the sporadic E trace at different frequencies as a constraint, we analyse the underlying lower thermospheric and ionospheric D-region characteristics, by applying a detailed coupled ion and neutral chemistry model SIC (Sodankyla Ion Chemistry model), together with modeling of the radio wave propagation and absorption. Use of a simplified ion chemistry model is compared with the use of the SIC model. While the expected effect of the solar eclipse on E-layer critical frequency cannot be seen due to the existence of the sporadic E layer, ionisation in the D-region is consistent with the variation of solar radiation during the eclipse.
SA41A-1554
Characteristics of convective rolls (overturning events) observed by the resonance lidars at different latitudes
One of the debated questions is the generation mechanism of convective rolls that have been studied using models and sodium lidar observations in the past. These studies have revealed strong overturning events in the bottom side of the Na layer. The earlier work has suggested that overturning in the Na density occurs before the gravity waves become unstable. Therefore, such Na density overturning may not be a good indication of unstable layers as the background atmosphere may still be stable during the events. Na mixing ratio and potential temperature appear to be a good indicator of atmosphere instability. Also, the earlier work has focused on measurements either from one location or single metal observations. Thus, it is important to look into this phenomenon in more details by combining additional data sets. The primary objective of the current research work is to characterize the convective rolls from four different locations with different latitudes or longitudes: Maui (20.7° N, 156.3° W), Arecibo (18.35° N, 66.75 ° W), SOR (35° N, 106.5° W), and Kyoto (35° N, 136° E). We will also examine the convective rolls in other metals than sodium. In order to characterize the properties of the events, we will investigate all three parameters: metal density, mixing ratio and potential temperature. Considering that there is a correlation between the convective instability and the occurrence of the overturning events, we expect that the latitudinal differences in the temperature should affect the occurrence probability of such events. In addition, this work intends to facilitate a better understanding of the occurrence of these events at the topside of the metal layer.
SA41A-1555
Self-consistent Diagnostics of SABER MLT Limb Radiances in the 15 and 4.3 um Channels
We performed detailed non-LTE analysis of contributions of various atmospheric layers and molecular trace gases into the daytime 15 and 4.3μm SABER channel MLT limb radiances. The updated forward fit retrieval algorithms was applied to the CO2 VMR retrievals from the 4.3μm radiances in the lower thermosphere with the simultaneous correction of the lower thermospheric temperatures retrieved from the 15μm channel. This combined analysis showed that replacement of the model CO2 VMRs applied currently for the operational temperature retrievals by those obtained from the 4.3μm channel can cause up to 5 K differences in retrieved temperatures depending on the season, latitude and solar insolation.
SA41A-1556
The NJIT-UACNJ-PSU Collaborative: A spatially scanning middle atmospheric lidar system in northwest New Jersey
We present an overview of a new middle and upper atmospheric observatory located in northwest New Jersey; focusing specifically on the 355-nm lidar system deployed in summer-early fall 2008. The lidar system uses a 1.2 W 355-nm laser system attached to a 1.2 meter, fully steerable optical telescope to measure a host of lower and middle atmospheric parameters, including a) lower and middle atmospheric gravity wave structures, b) lower atmospheric cloud/aerosol formations, and c) frontal systems as progenitors of gravity waves. These topics of interest are studied using 4D volume visualization methods often used in tropospheric Doppler radar systems.