SA41A-1031 0800h
Simultaneous TIMED/SABER and Ground-Based Measurements of the Semi-annual Oscillation in Mesospheric Temperatures
As part of a TIMED correlative ground-based research program long term measurements of the near IR mesospheric OH and O2 emissions have been made from USAF AEOS facility at the summit at Haleakala Crater, Maui, Hawaii (20.8N, 156.2W). Observations have been made routinely since October 2001 (typically 22 days/month) using the CEDAR Mesospheric Temperature Mapper (MTM). This imager sequentially measures the OH (6, 2) band intensity and temperature (peak altitude ~87km) and the O2 (0, 1) Atmospheric band intensity and temperature (peak altitude ~94km) with a precision of 1-2 K in 3 minutes.. To date, over 450 nights of quality data (durations typically 4 to 10 hours) have been obtained. A seasonal analysis of these data reveals a marked semi-annual oscillation (SAO) in temperature (and intensity) for both the OH and O2 emission data. The peaks in temperature (and intensity) data occurred during the Spring and Fall in good agreement with the well established SAO signatures in the mesospheric wind field. SAO signatures in mesospheric temperatures have previously been investigated using rocket and satellite borne techniques, but, ground-based observations are exceptionally few. In this paper we utilize zonally averaged SABER/TIMED data recorded during the 2002-2003 period to investigate seasonal variability in mesospheric temperatures and to look for a possible SAO signature and its amplitude variability with altitude. The results will be compared with our ground-based MTM analysis (which show a marked asymmetry in the oscillations peaking during northern hemisphere spring-time) to better quantify the SAO characteristics in the mesospheric temperature field.
SA41A-1032 0800h
Rate Coefficient for Collisional Removal of O$_2$($X^3\Sigma^-_g$, $v$ = 1) with O Atoms at 240 K
Knowledge of the water concentration profile is key to understanding of the chemistry and energy flow in the stratosphere and mesosphere. One of the tasks of the SABER instrument in NASA$'$s TIMED mission is to measure water vapor concentration by detecting H$_2$O($\nu_2$) emission in the 6.8 $\mu$m region. An important source of the H$_2$O($\nu_2$) emission is the collisional deactivation of vibrationally excited O$_2$: O$_2$($X^3\Sigma^-_g$, $v$ = 1) + H$_2$O $\leftrightarrow$ O$_2$($X^3\Sigma^-_g$, $v$ = 0) + H$_2$O($\nu_2$). For reliable interpretation of the SABER data it is crucial to determine rate coefficient for the competing process: O$_2$($X^3\Sigma^-_g$, $v$ = 1) + O($^3P$) $\rightarrow$ O$_2$($X^3\Sigma^-_g$, $v$ = 0) + O($^3P$) [1]. Laboratory measurements are reported of the rate coefficient for collisional removal of O$_2$($X^3\Sigma^-_g$, $v$ = 1) by O($^3P$) at a temperature of 240 K, relevant to the upper mesosphere. Instead of directly detecting the O$_2$($X^3\Sigma^-_g$, $v$ = 1) population, a novel, technically simpler, approach is used in which the $v$ = 1 level of the O$_2$($a^1\Delta_g$) state is monitored. With ground-state O$_2$ present, owing to the rapid equilibration of the O$_2$($X^3\Sigma^-_g$, $v$ = 1) and O$_2$($a^1\Delta_g$, $v$ = 1) populations via the processes O$_2$($a^1\Delta_g$, $v$ = 1) + O$_2$($X^3\Sigma^-_g$, $v$ = 0) $\leftrightarrow$ O$_2$($a^1\Delta_g$, $v$ = 0) + O$_2$($X^3\Sigma^-_g$, $v$ = 1), the information on the O$_2$($X^3\Sigma^-_g$, $v$ = 1) kinetics is extracted from the O$_2$($a^1\Delta_g$, $v$ = 1) temporal evolution. A two-laser method is employed, in which the pulsed output of the first laser near 285 nm photodissociates ozone to produce atomic oxygen and O$_2$($a^1\Delta_g$, $v$ = 1), and the pulsed output of the second laser detects O$_2$($a^1\Delta_g$, $v$ = 1) via the resonance-enhanced multiphoton ionization. In the same experiment, rate coefficients for removal of O$_2$($a^1\Delta_g$, $v$ = 1) with the atmospherically relevant colliders O$_2$, CO$_2$, and O also were measured at room temperature and 240 K. The measured rate coefficient for O$_2$($X^3\Sigma^-_g$, $v$ = 1) removal by O($^3P$) is in the range 2--3 $\times$ 10$^{-12}$ cm$^3$s$^{-1}$ at 240 K, compared to the recently measured room temperature value of about 3 $\times$ 10$^{-12}$ cm$^3$s$^{-1}$ [2]. Interestingly, removal of O$_2$($a^1\Delta_g$, $v$ = 1) by O($^3P$) is about five times less efficient than removal of O$_2$($X^3\Sigma^-_g$, $v$ = 1). The rate coefficient for O$_2$($a^1\Delta_g$, $v$ = 1) removal by O$_2$ is in the range 5--6 $\times$ 10$^{-11}$ cm$^3$s$^{-1}$ and is nearly temperature independent in the region 296--240 K. The removal by CO$_2$ is about 3000 times slower than removal by O$_2$ and nearly independent on temperature. Implications of the results for atmospheric modeling will be discussed. This work is supported by the NASA Geospace Sciences Program under grant NAG5-13002. Participation of Z. Campbell was made possible through the NSF Research Experience for Undergraduates Program under grant PHY-0353745. [1] M. G. Mlynczak, D. K. Zhou, M. Lopez-Puertas, G. Zaragoza, and J. M. Russell, Geophys. Res. Lett. 26, 63 (1999). [2] Konstantinos S. Kalogerakis, Richard A. Copeland, and Tom G. Slanger, Eos. Trans. AGU 82(47), Fall Meet. Suppl., Abstract SA41B-0728, 2001.
SA41A-1033 0800h
High-resolution Ion Drift Measurements from the JOULE Sounding Rocket Mission.
The JOULE sounding rocket mission was designed to investigate structured Joule dissipation in the auroral ionosphere. JOULE was launched March 27, 2003 from Poker Flat, Alaska, into an active substorm. The mission included two instrumented rockets and two chemical release (TMA) rockets in addition to ground-based diagnostics. One of the instrumented payloads carried a Suprathermal Ion Imager (SII) that measured 2-D (energy/angle) distributions of the core (0-8 eV) ion population at a rate of 125 images per second. In this presentation we compare bulk ion drifts derived from the SII with those inferred from DC electric fields. From differences in these two parameters we calculate the local Joule heating rate at a spatial resolution of 8 m.
SA41A-1034 0800h
Combined TIDI and Ground-Based Mesospheric Neutral Wind Observations
Using combined TIDI and ground based observations we study waves in the mesospheric and lower thermospheric neutral winds. We compare the neutral wind observations from spaceborne and ground-based measurements. We experiment with combine the neutral wind results from the two data sets. We hope the global coverage of the TIDI data and the extended local time coverage provided by the ground based observations will help to provide more insight of the MLT dynamics and energetics. Comparisons with model output are also planned.
SA41A-1035 0800h
Seasonal Variation of Mesospheric Ozone Over Three Decades
Mesospheric ozone has been measured over the last three decades from the Solar Mesosphere Explorer (SME: 1982-1986), High Resolution Doppler Imager (HRDI: 1992-1996) and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER: 2002-2004). Previous climatological studies of SME and HRDI ozone have shown that chemistry and dynamics play major roles in defining the seasonal variation. Both annual and semiannual oscillations are present indicating that factors affecting the seasonal variability in ozone include the distribution of water vapor and temperature, changes in solar insolation and tidal forcing. With the addition of an ozone climatology from SABER, this work compares the ozone seasonal variations as viewed by three satellites. In particular, we investigate how differences in satellite sampling can affect the perceived seasonal variations.
SA41A-1036 0800h
Electrodynamics of the Nighttime Equatorial Ionosphere: the Effects of Winds and Waves
In this paper we present initial results from two sounding rockets designed to study the coupling bewteen neutral winds and electric fields in the equatorial ionosphere. The combined instrumented and chemical release payloads were launched from Kwajalein in September 2004. The rockets carried instruments measuring electric fields, plasma densities, neutral densities, and was accompanied by a TMA release to profile neutral winds. Ground based airglow imagers and were used to determine mesospheric conditions; specifically, the presence of gravity waves. The goal of the experiment was to investigate correlations between the gravity wave wind structure and local electric fields. This coupling is expected to be appreciable at the equator, where the magnetic field is nearly horizontal. Here we present initial results and discuss plans for data analysis.
SA41A-1037 0800h
Comparisons of Measurements at Arecibo of the Gyro Line of Incoherent Scatter with the Theory
The gyro line of incoherent scatter is observed in the lower E region at Arecibo during the day. It is weak but still detected easily, and we have recently made measurements of sufficient quality to compare in detail with the predictions of the theory. The first step in a program to obtain useful geophysical information from this scatter is to verify that the results agree with predictions of the theory. Parameters contributing to the characteristics of the line are the electron gyro frequency, the look angle to the magnetic field, the electron density, and the electron temperature. The measurements are made with a long pulse for sensitivity reasons, and so the range resolution is not adequate to determine the location on profiles of density and temperature with sufficient accuracy for comparisons with the theory. Thus it is necessary to find a method to eliminate these two parameters from the comparison. After some time studying the theoretical predictions, it was discovered that the differences between the center frequencies of the lines at two different measurable look angles to the magnetic field are only very weak functions of the density and temperature. That is, although this frequency difference is a function of the electron gyro frequency and the look angle, it is not a strong function of the other two parameters. In effect, this frequency difference is known from the theory and the field parameters and consistency between prediction and the measurement is a check of the theory to a limit determined by the accuracy of the field parameters, the small residual variation due to the density and the temperature, and the random noise in the measurement. After a careful comparison with the data from October 21, 2001, we have determined that the measured difference is too small for agreement with the theory. We are now checking for why this might be so and attempting to make comparisons with other available data sets.
SA41A-1038 0800h
MLT cooling at Resolute Bay(74\deg N, 94\deg W), Canada
Observations of the MLT (Mesosphere and Lower Thermosphere) show a strong coupling to the stratosphere through adiabatic cooling and warming effects. This arises from energy and momentum input to the MLT by propagating waves from the lower atmosphere.The dynamical forcing causes upwelling in the mesosphere and downwelling in the stratosphere, giving rise to a stratospheric sudden warming. To explore this relationship an optical instrument called SATI (Spectral Airglow Temperature Imager) was installed at Resolute Bay (74\deg N, 94\deg W), November, 2001 and observations have been made for three winter seasons. The SATI measures emission rates and temperatures from the O$_2$(0$-$1) atmospheric band at an altitude of 94 km and from the OH(6$-$2) Meinel band nightglow at 87 km. The three winters were very different in the characteristics of their temperature perturbations. The strongest mesospheric coolings related to the stratospheric sudden warming (SSW) were found from 2001/2002 winter season data. These events were compared with the stratospheric assimilated data provided by UKMO (UK Meteorological Office) and the TIME-GCM$/$CCM3 (National Center for Atmospheric Research Thermosphere, Ionosphere, Mesosphere, and Electrodynamics General Circulation Model$/$Climate Community Model Version 3) predictions of Liu & Roble.
SA41A-1039 0800h
Evidence for a new Production Mechanism for the Singlet Delta State of Molecular Oxygen
The InfraRed Imager subsection of the OSIRIS instrument onboard the Odin spacecraft collects limb images of the Oxygen InfraRed Atmospheric band emissions at 1.27 microns. The dusk-dawn orbit of the Odin spacecraft means the evening twilight sector of the orbit is near the equator and as a result the tomographic retrieval technique used to process the InfraRed Imager data produces high resolution two-dimensional profiles of the singlet delta volume emission rate as the sun sets. For the times of year under consideration the actual sunset data extends from the equator to approximately 20 degrees latitude. Accepting the limitation that the satellite geometry means different solar zenith angles are viewed at different latitudes this work will use the InfraRed Imager measurements along with the accepted radiative lifetime and quenching coefficients to show that after the sun sets the singlet delta state of molecular oxygen does not decay as quickly as expected. If the accepted values are indeed correct the only explanation for the decrease in decay rate is that there is a production mechanism that has not been considered. The OSIRIS measurements indicate that this production mechanism is layered with a peak around 60 km.
SA41A-1040 0800h
A Prototype Near-IR Mesospheric Imaging Michelson Interferometer (MIMI) for Atmospheric Wind Measurement
A prototype optical instrument for the simultaneous observation of airglow intensities and winds, through doppler shifted emission lines, has been designed and is currently operating at York University. The Mesospheric Imaging Michelson Interferometer (MIMI) has successfully retrieved simulated winds in the laboratory using visible wavelengths with an error less than 1 m s$^{-1}$ and in the near-IR region to better than 2 m s$^{-1}$. The instrument operating theory and four point wind retrieval technique will be discussed in addition to current work focusing on efforts to observe winds from a ground based instrument.
SA41A-1041 0800h
Absolute Intensities of the OH Meinel bands in the Nightglow
Flux-calibrated high resolution spectra of the night sky have been accumulated for the spectral region of 314 - 1054 nm. The spectra are obtained from two sources: (a) the ESI spectrograph on the Keck II telescope at Mauna Kea with a spectral resolution of 6000 and a temporal resolution of 3000 seconds and (b) coadded spectra (1) from the UVES spectrograph on the VLT (Kueyen) telescope at Cerro Paranal with a spectral resolution of 50000. Emission from the OH X$^{2}\Pi$(v'=3-9) Meinel bands are prominent in the spectra allowing absolute intensities to be measured for discrete rotational lines in the main rotational branches for 16 vibrational bands in the ESI spectra ($\Delta$v = -6 to -3) and 20 vibrational bands in the UVES spectrum ($\Delta$v = -7 to -3). Comparison of the band intensities to the earlier photographic measurements of Krassovsky et al.(2) show a systematic deviation with wavelength similar to that deduced by Adler-Golden(3). Several emission bands are observed from most upper state vibrational levels. Comparisons of the band intensity ratios and the rotational branch intensity ratios for these bands show systematic deviations from those calculated using the existing sets of emission coefficients. Progress will be reported on the re-evaluation of the dipole moment function (4) using the present absolute intensities to obtain an improved set of OH emission coefficients. This work was partially supported by NSF grant ATM-0139344. (1) R. W. Hanuschik, Astron. Astrophys. {\bf 112}, 1157 (2003). (2) V. I. Krassovsky et al., Planet. Space Sci. {\bf 9}, 883 (1962). (3) S. Adler-Golden, J. Geophys. Res. {\bf 102}, 19969 (1997). (4) D. D. Nelson et al., J. Chem. Phys. {\bf 93}, 7003 (1990).
SA41A-1042 0800h
Vertical Heat and Constituent Transport in the Mesopause Region by Dissipating Gravity Waves at Maui, HI (20.7N) and Starfire Optical Range, NM (35N)
Vertical heat flux profiles induced by dissipating gravity waves in the mesopause region (85-100 km altitude) are derived from Na lidar measurements of winds and temperatures at Maui (20.7N, 156.3W), HI and compared with earlier results from Starfire Optical Range (SOR, 35.0N, 106.5W), NM. The heat flux profile at SOR has a single downward maximum of 2.25$\pm$0.3 Km/s at 88 km, while the profile at Maui has two downward maxima of 1.25$\pm$0.5 Km/s and 1.40$\pm$0.5 Km/s at 87 and 95 km, respectively. The common maximum below 90 km can be attributed to high probability of convectively instability. Comparison of the horizontal wind shear suggests that the second maximum at 95 km at Maui may be associated with dynamic instability. The measured Na flux and predicted Na flux based on measured heat flux at Maui agree well, further confirming earlier findings using SOR data. The dynamical flux of atomic oxygen estimated from the heat flux is smaller at Maui compared with that at SOR, but both are comparable to or larger than the eddy flux. The results also suggest that weaker gravity wave dissipation at Maui may cause two opposite effects on the energy balance in the mesopause region, a reduced cooling from heat transport and reduced chemical heating from atomic oxygen transport.
SA41A-1043 0800h
Analysis of the SABER 4.3-$\mu$m Nighttime Radiance and Implications for the Temperature and CO$_2$ vmr Retrieval
The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument measures the CO$_2$ 4.3-$\mu$m nighttime emission with a signal-to-noise ratio which equals to 1 at 130 km. These measurements can be used to derive the carbon dioxide abundance above 75\,km during nighttime. CO$_2$ abundance is needed not only to understand the energy balance of the MLT region but also to accurately derive the kinetic temperature in that region from the measurements taken at 15-$\mu$m. However, the nighttime non-LTE mechanisms affecting the 4.3-$\mu$m CO$_2$ vibrational state population are not well known and therefore CO$_2$ abundance cannot still be accurately retrieved from SABER measurements at night. The analysis of SABER nighttime measurements at 4.3-$\mu$m presented here shows that the radiance is reproduced only if an efficient energy transfer from OH to CO$_2$ via N$_2$ , whereby 2.8-3 N$_2$(1) molecules are excited after quenching of one OH($\upsilon$), is considered. We also present the implications of including such a process in the simultaneous T$_k$/CO$_2$ retrieval results.
SA41A-1044 0800h
QBO Generated Inter-annual Variations of the Diurnal Tide in the Mesosphere
In preparation for the measurements from the TIMED mission, we report results from a study with the Numerical Spectral Model (NSM), which produces in the diurnal tide significant inter-annual variations. Applying Hines' Doppler Spread Parameterization (DPS), small-scale gravity waves (GW) drive the Quasi-biennial Oscillation (QBO) and Semi-annual Oscillation (SAO). With a GW source that peaks at the equator and is taken to be isotropic and independent of season, the NSM generates a QBO with variable periods around 27 months and zonal wind amplitudes close to 20 m/s at 30 km. As reported earlier, the NSM reproduces the observed equinoctial maxima in the diurnal tide at altitudes around 95 km. In the present paper it is shown that the QBO modulates the tide such that the seasonal amplitude maxima can vary from one year to another by as much as 30%. Since the period of the QBO is variable, its phase relative to the seasonal cycle changes. The magnitude of the QBO modulation of the tide thus varies considerably as our long-term model simulation shows. To shed light on the underlying mechanisms, we discuss (a) the relative importance of the linearized advection terms that involve the meridional and vertical winds of the diurnal tide and (b) the effects of momentum deposition from GWs filtered by the QBO zonal winds.
SA41A-1045 0800h
Determining tidal-period perturbations from less than full-diurnal cycle time series
Lidar and radar observation can now be performed continuously for several complete diurnal cycles. Though diurnal and semidiurnal amplitudes are typically larger than the terdiurnal and quatradiurnal counterparts, depending on season and latitude, such is, however, not always the case. For the long-period continuous data sets decomposition into tidal-period oscillations with diurnal, semidiurnal, terdiurnal and quatradiurnal components is unique. Often, the data sets shorter than a full-diurnal cycle coverage are nonetheless of considerable interest, because of the need to assess the contribution of tidal-period perturbation to atmospheric instability or the tidal variability due to gravity wave interaction which may be very strong. Unfortunately, data shorter than one complete diurnal cycle admits diverse decomposition, depending how many terms are included in the analysis. In this paper, we use synthetic data with reasonable amplitudes to assess the variability or uncertainty of deduced tidal components due to different relative phases of the actual tides, due to different assumed components in the analysis, as well as due to the length of data sets and the presence of gaps. We then discuss these findings by investigating a 9-day continuous data set and two other sets each with 16 hours of data, all acquired in September by our two-beam lidar, capable of measuring temperature, zonal and meridional wind in the mesopause region.
SA41A-1046 0800h
First Simultaneous MLT and Thermospheric F-region Observations
Earth's thermosphere and the embedded ionosphere, called the thermospheric F region, have been studied in numerous publications. From these studies, it is known that complete understanding of the behavior of the thermospheric F region requires its coupling to the magnetosphere above and the mesosphere lower-thermosphere (MLT) region below. Recently, we have started observing the MLT and thermospheric F regions simultaneously by operating the MU radar (35$^{\circ}$N, 136$^{\circ}$E) in alternate meteor and incoherent scatter (IS) modes under a project called MTEC-S (Mesosphere Thermosphere Experiments for Coupling Studies), with a view to identify the tides and waves that can dynamically couple the upper atmospheric regions. The MTEC-S observations (each lasting more than a week) provide simultaneous zonal and meridional wind velocities at MLT altitudes (80-95 km), meridional wind velocity in the upper thermosphere (220-450 km), and electron density (150-600 km), peak height and plasma drift velocity in the ionosphere with a time resolution of 1.5 hours. The long data sets, one in each season during 2000-01, and their spectra are used to obtain the mean winds, and tides and waves that can couple the MLT and thermospheric F regions in different seasons. The seasonal and solar activity dependencies of the mean wind velocity and tidal amplitudes (of periods 24 and 12 hours) at the MLT and thermospheric F region altitudes are also presented.
SA41A-1047 0800h
A curved gravity-wave structure in the mesospheric airglow images
We found a unique wave structure, which had arc-like curved wave fronts in high contrast, by using an all-sky airglow imager located at Shigaraki (34.9N, 136.1E) on October 3, 2002. The curved structures were identified over 2.5 hours (1330-1600UT: 2230-0100LT) both in the OI (557.7 nm, emission altitude: 96 km) and OH-band (720-910 nm, 86 km) images. The wave structures had a wavelength of about 40 km and propagated northeastward with a horizontal phase velocity of about 100 m/s. Assuming that each wave pattern originated from a point source in the troposphere, the center of the curvature was projected on the sea near the tip of the Kii peninsula (33.5N, 135.1E). In the presentation, we will discuss three-dimensional structure of the curved pattern of gravity waves using image data of two airglow emissions at different altitudes, background wind data obtained simultaneously by the MU radar, and meteorological data obtained from ground and satellite.
SA41A-1048 0800h
Impact of E-Region Ion-Neutral Chemistry on SABER Measurements of 4.3 um Emission and the Retrieval of Kinetic Temperature and Carbon Dioxide
The TIMED/SABER experiment is based on broadband limb emission measurements. Measurements from the 4.3 um channel, in particular, are strongly enhanced during nighttime aurora. Auroral particle precipitation increases the ionization of the neutral atmosphere, followed by fast ion-neutral exothermic reactions that produce vibrationally excited NO+ (i.e., NO+(v)), which promptly emits at 4.3 um. Therefore, SABER 4.3 um measurements provide a unique tool for observing and analyzing the E-region response to auroral particle energy deposition, as NO+ is the terminal E-region ion. We use SABER data products and 4.3 um measurements, the field-line interhemispheric plasma (FLIP) model, measurements of auroral particle energy characteristics from the NOAA/POES satellites, and radiation transfer algorithms to analyze the ion-neutral energy transfer mechanisms that produce NO+(v) and emission at 4.3 um during the April 2002 and October-November 2003 solar storms. Furthermore, since SABER kinetic temperature (Tk) and CO2 are simultaneously retrieved from the 15 um and 4.3 um channel measurements, respectively, NO+(v) 4.3 um emission can introduce biases in the SABER Tk/CO2 retrievals at polar latitudes even during quiescent conditions, with maximum biases occurring at summer solstice. Moreover, sensitivity studies are conducted to assess potential biases in SABER Tk/CO2 due to contamination by NO+(v) 4.3 um emission.
SA41A-1049 0800h
Investigation of observed day-to-day variability in September mesopause region tidal-period perturbations
Simultaneous observations of the tidal-period perturbations (diurnal, semidiurnal, .etc) of temperature, zonal wind, and meridional wind in the mesopause region (80km-105km) by the CSU two-beam Na lidar system in Fort Collins, Colorado between UT day 264 and 272, September 2003 (a 9-day continuous campaign) indicate a dramatic day-to-day variability on tidal amplitudes. Further analysis on the dataset with best fit to tidal perturbations within a running 24hr window reveals that in addition to diurnal and semidiurnal tides, there exist 3-day and 5-day waves. We also observed a 2-fold increase in amplitudes of temperature, zonal and meridional wind tides on the day 267-268. Whether this is the result of tidal-gravity wave nonlinear interaction, or of planetary wave modulation is the main objective of this paper. Time series of the temperature vertical profiles for day 267 shows a strong temperature inversion with a near adiabatic lapse rate above. We find that at the altitude near adiabatic lapse rate, the semidiurnal and diurnal tides are in-phase so that the total negative temperature gradient due to tidal contribution was increased to near adiabatic lapse rate. The observed temperature inversion and accompanying change in zonal wind are consistent with wave breaking. Analysis in this direction invoking both TIME-GCM simulation and TIMED/SABER observed temperatures providing a global perspective will be made.
SA41A-1050 0800h
Diurnal Tidal Variability Over the Equator: Model and Measurement Comparisons
We compare equatorial migrating diurnal temperature estimates determined from measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite with predictions from the NCAR Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) and the Global-Scale Wave Model (GSWM). We contrast the full model tidal results with diurnal tidal estimates determined from subsets of temperature predictions that represent what SABER would observe if it flew through the model atmospheres. Comparisons between the full and satellite sampled model temperatures suggest that there may be strong artifacts of the semidiurnal tide in the SABER diurnal tidal estimates above ~100 km.
SA41A-1051 0800h
Variability of Atomic Oxygen and its Effect on the Energy Budget Near the Mesopause
Atomic oxygen plays a crucial role in determining the energy budget near the mesopause region of the atmosphere. The rates of important exothermic reactions depend either directly or indirectly on its concentration, as does the rate at which energy is lost through airglow emissions. Measurements of these emissions can thus be used to infer atomic oxygen densities and, through the use photochemical models, chemical heating rates. This work presents a three-way intercomparison of atomic oxygen derived from airglow observations made by the UARS-WINDII and TIMED-SABER instruments, and simulations using a global chemical-dynamical model. All datasets reveal significant seasonal and diurnal variability in atomic oxygen and so chemical heating rates, and again demonstrates the need to quantify constituent variability when examining the mesopause energy budget.
SA41A-1052 0800h
Lidar Measurements of the MLT Thermal Structure At Maui, HI (20.7°N) And Starfire Optical Range, NM (35°N)
The University of Illinois Na wind/temperature lidar was coupled to large astronomical telescopes at the Starfire Optical Range (SOR) in Albuquerque, New Mexico (35.0°N, 106.5°W), and at the Maui Space Surveillance Complex on the top of the Haleakala in Maui, Hawaii (20.7°N, 156.3°W). Hundreds of hours of high-quality temperature and wind data have been collected at these two locations. This provided us a good opportunity to study the subtropical thermal structure of the mesosphere and lower thermosphere (MLT) region, and make comparisons with mid-latitudes. We also compared the observations with the MSIS-00 model. Both locations exhibit mesospheric temperature inversion layers (MIL) between 85 and 100 km, which are not predicted by the MSIS-00 model. The amplitudes of the Maui MILs are about half of those at SOR and the Maui MILs have a smaller width compared to the SOR MILs. The Maui lidar temperatures are generally warmer than the MSIS-00 predictions, while the SOR lidar data are comparable to the MSIS-00 except in the MIL altitude range. Both SOR and Maui mesopause temperatures are coldest in mid-summer and warmest during the mesopause transition periods. However, the Maui mesopause is warmer than the SOR, and the amplitude of the mesopause temperature variations at Maui is much smaller than at SOR. Two distinct levels of mesopause altitudes are clearly shown in the SOR seasonal data with a low altitude around 86.5 km in summer (May through August) and a high altitude around 101 km during the rest of the year. Abrupt transitions between the two stable levels occur in early May and early September. At Maui, the lidar measurements indicate a low mesopause altitude near 87.5 km in July when averaging over a 10-h period centered at local midnight. Tides strongly influence the MLT temperature and the mesopause structure. The composite night in July shows that the lowest temperature is near 87.5 km at the beginning of the night and then switches to a higher altitude around 100 km after local midnight. With the semi-diurnal tides removed from the data, the composite night indicates that the mesopause stays at the low altitude through most of the night in July at Maui.
SA41A-1053 0800h
Global and Seasonal Distributions of Mesospheric OH Emissions from SABER
On December 7, 2001, SABER, a cooled multichannel radiometer, was launched aboard the TIMED satellite. In January of 2002 the SABER instrument began returning airglow limb scan measurements from around the globe. Data now available include 65% of 2002, 75% of 2003, and 40% of 2004. Experimental data were taken from SABER for two radiometric channels centered at $\lambda$=1.6 $\mu$m and 2.06 $\mu$m. Volume emission rates (VER) were computed at the peaks of the OH layer profiles and then the magnitudes were displayed as a function of the latitude and longitude of the tangent point of the observation. The Mlynczak unfiltering algorithm for OH emissions was used to obtain absolute values for the maximum VER of the total sequence of OH vibration-rotation band emissions. The maximum VER was found to be greater near the equator compared with high latitudes. In addition, seasonal effects on the global distribution of the nighttime OH airglow were explored for the available data in 2002, 2003, and part of 2004. Algorithmic methods of optimized geographic visualization for this unprecedented wealth of mesospheric airglow data were also explored.
SA41A-1054 0800h
Coordinated Ground and Space Based Observations of the Quasi Two-Day Wave in January 2004
The quasi two-day wave is a predominant feature of the mesosphere and lower thermosphere during January and early February each year with horizontal wind speeds exceeding 50 m/s and temperature perturbations on the order of 14K. Theoretical and modeling results indicate the quasi two-day wave is initiated through a baroclinic instability of the summer westward mesospheric jet. The global quasi two-day wave response is repeatable from year to year and is the result of the 3,0 Rossby normal mode being forced by the instability. Observations from the TIMED spacecraft in January 2004 have provided the first opportunity to study the global structure and evolution of the quasi two-day with measurements of both the temperature and horizontal wind field. These measurements from the mesosphere into the lower-thermosphere are provided from the SABER and TIDI instruments on TIMED. These observations will be combined with observations from the global network of ground-based meteor and medium frequency radars to provide a comprehensive view of the quasi two-day wave observed during January 2004.
SA41A-1055 0800h
Evidence for a Solar Cycle Variation in Nightglow and Atomic Oxygen in the Mesosphere and Lower Thermosphere.
Six years of UARS/WINDII nightglow data have been used to derive atomic oxygen mixing ratios from the 80 to 110 km. This data set extends from winter 1991 to 1996 and ranges from shortly after solar maximum to solar minimum. Inter-annual variations in the derived mixing ratio are observed. This variation is in addition to the local time, seasonal and annual variations previously identified in this data set. Above ~90 km there is a positive correlation between the solar cycle and the oxygen mixing ratio as would be expected given the solar cycle dependence of its source in the thermosphere (dissociation of molecular oxygen). The decrease at these heights is by more than 50%. The correlation changes sign below this height and the mixing ratio increases by about 50%. A decrease in the peak height of the hydroxyl and oxygen green line nightglow layer is also observed during this time period. Associated variations are expected in the chemistry and energetics of the mesosphere and lower thermosphere.
SA41A-1056 0800h
Morphological Studies of Mesospheric Chemical Heating Rates Using HRDI/UARS and SABER/TIMED Measurements
Several exothermic chemical reactions involving atomic oxygen, atomic hydrogen, and ozone are important heating sources in the mesosphere. These reactions also are directly or indirectly responsible for the airglow emissions in this altitude region. The rates for these airglow emissions, specifically the O($^1$S) greenline, O$_2$($^1\Sigma$), O$_2$($^1\Delta$), and OH Meinel bands, thus provide measurements of the chemical heating rates important for our understanding of mesospheric energetics. In this paper, we present the observed chemical heating rates of O+O+M, O+O$_2$+M, and H+O$_3$ reactions from nightglow emission rates measurements taken by the High Resolution Doppler Imager (HRDI) instrument onboard the Upper Atmosphere Research Satellite (UARS) and the Soundings of Atmosphere Using Broadband Emission Spectroscopy (SABER) instrument onboard Thermosphere-Ionosphere-Mesosphere, Energetics and Dynamics (TIMED). The temporal and spatial morphology of these chemical heating rates will be presented.
SA41A-1057 0800h
Collaborative analysis of Planetary Waves in the Mesospheric Neutral Winds with SuperDARN and TIMED Observations
The SuperDARN HF radars are best known for observing the ExB drift of ionospheric plasma in the high-latitude F region. At mesospheric altitudes the trails of ionization produced by meteors provide another kind of target for radar backscatter, and the motions imparted to these trails by winds in the neutral atmosphere can be measured. In the northern hemisphere the coverage of mesospheric winds currently extends over a 180 deg longitude sector but is confined by propagation conditions to latitudes near 55 deg geographic. We have analyzed several extended periods of simultaneous observations of the neutral wind involving SuperDARN and the TIMED suite of instruments. Often, the winds show clear evidence of large-scale wave events. The quasi 2-day planetary waves are prominent and their occurrence is seen to depend on season. By comparing the wave characteristics between the satellite and ground observations we obtain a complete breakdown of the wave activity in terms of wave periods and zonal wavenumbers. In addition, the semidiurnal tide is a ubiquitous feature of the mid-latitude mesosphere. A single radar station cannot resolve the sun-synchronous component from other contributions at the semidiurnal frequency. We show that with a chain of radars along a latitude band, the true sun-synchronous, or migrating, component can be inferred. Joint analysis can be performed chiefly with data from the SABRE and TIDI instruments.
SA41A-1058 0800h
A Data assimilation model for determining the mean state and migrating tide structures in the mesosphere and lower thermosphere using TIMED measurements of wind and temperature
One of the main goals of the TIMED mission is to characterize the structure of the mean winds and the migrating tides in the mesosphere and lower thermosphere (MLT). This task is made difficult by the fact that the zonal mean and migrating tides are aliased in satellite measurements of any dynamic or constituent field. The typical approach to separating the mean and tidal components in a single measured field is to use the satellite precession to scan in local time and then use harmonic analysis on the local time dependence of the measured field. This approach assumes that the tide and mean components are steady during the time it takes for the satellite to complete a full yaw cycle, but this assumption is far from true in light of the 60 day yaw cycle of TIMED. Attempts to use data from a partial yaw cycle will run into other difficulties. A new approach to the tidal analysis of satellite data has been developed and shown successful on data from HRDI/UARS. Our approach relies on the simultaneous measurement of wind and temperature fields to separate the mean and tidal components and incorporates data assimilation techniques into a steady-state model of the mean winds and migrating tides. This technique can be applied to obtain results from only a single day's measurements of winds from TIDI and temperatures from SABER. Unlike assimilation techniques used in weather forecasting, which rely on slow manifold balance conditions, this new technique relies on the assumption of geostrophic balance for the mean winds and the ageostrophic balance implied by the tidal equations. The fact that different balance conditions apply to the mean and tidal components enables their separation if wind and temperature measurements are used simultaneously. The tidal model uses the theory of generalized Hough modes developed by the PI to incorporate the effect of mean winds and damping (from gravity waves and molecular diffusion) on tidal structure. The sensitivity of tidal structure to damping enables information to be derived on the magnitude of damping effectively applied to the tides.