High Resolution Doppler Imager Research Articles

Repeatability of high-resolution laser Doppler images of the hands in patients with systemic sclerosis and secondary Raynaud's phenomenon.

The objective of the study was to establish the repeatability of baseline diagnostic images of the dorsum of the hands acquired using a high-resolution laser Doppler imager in patients with Raynaud's phenomenon secondary to systemic sclerosis (SSc). The dorsal side of the hands of 22 patients (8 male 14 female), age range 29-73, median 62, with SSc and secondary Raynaud's phenomenon were imaged over two consecutive days at approximately the same time using a Moor Instruments' high-resolution laser Doppler imaging unit. The images were analysed by taking regions of interest at discrete locations in the images to calculate dimensionless values of flux (PU). Repeatability of the diagnostic investigation was assessed using methods described by Bland and Altman and by also plotting the results from visit 1 against visit 2 and calculating the line of best fit. Based on the criteria that 95% of all measurement differences should be within a factor of 1.96 of the standard deviations of the mean values, then high-resolution laser Doppler imaging technique is probably repeatable when acquiring and analysing baseline images of patients with Raynaud's phenomenon secondary to SSc. However, a larger study with more patients is required to prove this conclusively-as only data from 19 patients were analysed (3 patients were not included due to technical issues)-and was therefore susceptible to marked clinical variations in patients presenting on different days for the investigations.

Neurogenic Flare Response following Image-Guided Focused Ultrasound in the Mouse Peripheral Nervous System in Vivo

Focused ultrasound (FUS) has been used to non-invasively elicit or inhibit motor neuronal activity in the mouse peripheral nervous system in vivo. However, less is known about whether FUS elicits immune system responses associated with peripheral sensory neuronal activity. In this study, we sought to determine that non-invasive ultrasound image-guided FUS can elicit the neurogenic axon reflex of peripheral nerves in the mouse sciatic nerve. The local vasodilation in the plantar view of the hind paw detected with a high-resolution laser Doppler imager indicated neurogenic flare responses after FUS stimulation. The effects of FUS were compared with control groups, where a distinct pattern of blood flow changes was observed only in FUS-elicited neurogenic flare responses. The findings indicate that image-guided FUS elicits local axon reflexes in vivo with a high degree of specificity and penetration depth.

Long‐Term Trends in the Low‐Latitude Middle Atmosphere Temperature and Winds: Observations and WACCM‐X Model Simulations

AbstractIn recent years, the middle atmosphere has evoked great scientific interest as long‐term changes can be clearly captured owing to the large perturbation amplitudes at these altitudes. In the present study, more than 25 years of the data are used to investigate the long‐term trends in the middle atmosphere by suitably combining the observations from different techniques (Rocketsonde, High‐Resolution Doppler Imager (HRDI)/Upper Atmosphere Research Satellite (UARS), Halogen Occultation Experiment (HALOE)/UARS, Sounding of the Atmosphere using Broadband Emission Radiometry (SABER)/Thermosphere Ionosphere Mesosphere Energetic Dynamics (TIMED), and Mesosphere‐stratosphere‐troposphere (MST) radar) from Indian region. As different instruments/techniques are used and the time periods are not the same, extreme care has been taken while merging various data sets to obtain meaningful long‐term trends. To understand the observed long‐term trends, Whole Atmosphere Community Climate Model–eXtended model simulations for the Indian low‐latitude regions are also used. A significant cooling trend of ~−1.7 ± 0.5 K/decade between 30 and 80 km is noticed. Large decreasing trend (~5 m/s/decade) in the eastward winds is noticed which is significant between 70 and 80 km only changing from strong eastward wind in 1970s to weak westward wind in recent decade. No significant trends are observed in the meridional wind. These observations are well captured by the Whole Atmosphere Community Climate Model–eXtended model simulations while considering changes in concentrations of greenhouse gases including carbon dioxide (CO2), methane (CH4), water vapor (H2O), and chlorofluorocarbon species that cause depletion of stratospheric ozone (O3). Thus, it is prudent to conclude that long‐term decreasing trends in the zonal winds and cooling trends in the temperature in the middle atmosphere are caused to a large extent by greenhouse gases suggesting the role of anthropogenic changes in the dynamics of the middle atmosphere.

SWIFT-DASH: Spatial Heterodyne Spectroscopy Approach to Stratospheric Wind and Ozone Measurement

Passive wind measurements using Doppler shifts from atmospheric emissions were well demonstrated by the Wind Imaging Interferometer (WINDII) and the High Resolution Doppler Imager (HRDI) instruments on the National Aeronautics and Space Administration's (NASA's) Upper Atmosphere Research Satellite, operated from 1991 to 2005. For WINDII these emissions were from visible region upper atmospheric airglow in the altitude range from 80 to 300 km. Application of the same technique in the stratosphere requires using thermal emission from a minor constituent, and an ozone line near 1133 cm−1 (about 8.8 μm) has been identified as a suitable target line. The WINDII method employed a Doppler Michelson Interferometer, in which the wind is measured from phase shifts of a single spectral line. Isolating a single ozone spectral line is a major challenge but using Spatial Heterodyne Spectroscopy (SHS) offers a way to resolve a number of interferogram spectral components (fringes) within a narrow spectral range. The instrument is a Michelson interferometer similar to WINDII but one in which the two mirrors are replaced by diffraction gratings. A developmental instrument capable of measuring the phase shifts from several ozone lines within a spectral range of 4 cm−1 has been designed, built, and operated in the laboratory. Simulated retrievals using the measurement parameters of this instrument demonstrate the capability of wind measurement with an accuracy better than 3 m s−1 over an altitude range of 24 to 60 km. The retrieval employs four spectral lines for wind and three fringe frequencies for ozone concentration (of about 30 possible), each of which provides an optimal measurement for a particular altitude range. Ozone concentrations are also provided with an accuracy better than 10% from 20 to 50 km. Further detailed tests of this instrument are planned for the future. This work is supported by the Canadian Space Agency.

Nonmigrating diurnal tides observed in global thermospheric winds

Nonmigrating diurnal tides between 90 and 270 km are inferred from Upper Atmosphere Research Satellite (UARS) wind imaging interferometer (WINDII) winds. This study represents the first known effort to directly analyze tidal wave number structure and propagation direction in winds observed over this altitude range. Prominent diurnal tides include an eastward propagating wave number 3, a zonally symmetric tide, and a westward propagating wave number 2. UARS High Resolution Doppler Imager winds between 60 and 100 km were analyzed identically and show excellent consistency with WINDII tides. Observed tides were compared with tidal fits to Hough Mode Extensions. WINDII tides are generally damped more slowly above 120 km than fitted tides, and the zonally symmetric tide indicates a thermospheric source not captured by Hough Mode Extensions. Our study provides additional confirmation that tides act as direct coupling agents between the troposphere and the thermosphere (and F region), in addition to their role in the E region dynamo.

Lunar tidal winds between 80 and 110 km from UARS/HRDI wind measurements

Recent observations and models show the considerable effects of upward‐propagating lunar atmospheric tides on many aspects of the ionosphere‐thermosphere system. A key aspect of atmosphere‐ionosphere coupling is the wind field in the ionospheric E region (circa 100–150 km), where the dynamo generation of electric fields occurs. Yet, global specifications of lunar tidal winds exist only in theoretical predictions although years of satellite observations on atmospheric winds exist with almost global coverage. In the present paper, we report on quasi‐global semidiurnal lunar tidal winds up to 115 km from data gathered by the High Resolution Doppler Imager (HRDI) on board the Upper Atmosphere Research Satellite during the early years from 1991 to 1999. The observed lunar semidiurnal tidal winds are consistent with global scale wave model (GSWM) simulations in both amplitude and phase, with maximum amplitudes located between about ±40°N–60°N around the solstices. The peak amplitudes of the lunar tidal winds lie in the 10–15 ms−1range, whereas those simulated by GSWM lie between 15 and 25 ms−1. The smaller HRDI amplitudes are likely due in part to amplitude suppression in construction of the climatological mean resulting from year‐to‐year phase variability in the lunar tide. It is also possible that wave dissipation is underestimated to some degree in the GSWM.

Satellite observations of ozone in the upper mesosphere

Ozone profiles in the upper mesosphere (70–100 km) retrieved from nine instruments are compared. Ozone from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument is used as the basis of comparison. Other measurements are from the Halogen Occultation Experiment, the High Resolution Doppler Imager, the Michelson Interferometer for Passive Atmospheric Sounding, the Global Ozone Monitoring by Occultation of Stars, the Atmospheric Chemistry Experiment—Fourier Transform Spectrometer, the Solar Occultation For Ice Experiment, the Optical Spectrograph and InfraRed Imaging System, and the Superconducting Submillimeter‐Wave Limb‐Emission Sounder. Comparisons of each data set with SABER using coincident profiles indicate agreement in the basic vertical profile of ozone but also some systematic differences in daytime ozone. Ozone from the SABER 9.6 μm channel is higher than the other measurements over the altitude range 60–80 km by 20–50%. Nighttime comparisons indicate better relative agreement (<10% difference). Taking all the data, not limited to coincidences, shows the global and seasonal distributions of ozone in the upper mesosphere from each instrument. The average maximum in ozone mixing ratio is around 90–92 km during daytime and 95 km at night. There is a maximum in ozone density at night (∼90 km) and during some hours of the day. The latitude structure of ozone has appreciable variations with season, particularly in the tropical upper mesosphere. The basic latitude‐altitude structure of ozone depends on local time, even when the analysis is restricted to day‐only observations.

Mesospheric wind diurnal tides within the Canadian Middle Atmosphere Model Data Assimilation System

The horizontal wind data from the standard version of Canadian Middle Atmosphere Model Data Assimilation System (CMAM-DAS) have been analyzed to obtain the diurnal wind structures in the mesosphere. In the standard version of CMAM-DAS, meteorological observations from radiosondes, aircraft, surface measurements, and satellites are assimilated only in the troposphere and stratosphere (below 1-hPa) with no increments applied in the mesosphere. Results for the years 2006–2008 are being used here as part of the Canadian International Polar Year (IPY) program and the Canadian Network for the Detection of Atmospheric Change (CANDAC) Research Program. The CMAM-DAS shows good overall agreement with radar observations for the seasonal characteristics of the diurnal tides at single stations from low-middle latitudes. The most prominent nonmigrating diurnal tides revealed by the CMAM-DAS winds at 88 km include the westward propagating component with zonal wavenumber 2 (DW2), the standing oscillation (D0), and the eastward propagating wavenumbers 3 (DE3) and 2 (DE2). A detailed discussion of the latitudinal and seasonal variations and Hough modes is provided for these predominant nonmigrating components and the migrating tide (DW1). The modeled nonmigrating diurnal tides, on both monthly (60-day windows) and annual time scales, are generally in good agreement with those determined from TIDI (TIMED Doppler interferometer) and from UARS-HRDI (High Resolution Doppler Imager)/WINDII (Wind Imaging Interferometer). This work provides further evidence for the tidal forcing from below.

Mesospheric wind semidiurnal tides within the Canadian Middle Atmosphere Model Data Assimilation System

[1] The horizontal wind data from the standard version of Canadian Middle Atmosphere Model Data Assimilation System (CMAM-DAS) for the years 2006–2008 are analyzed to obtain the global structure and seasonal variability of the semidiurnal tide (SDT) in the mesosphere. The modeled amplitudes and phases of the SDTs at single stations from middle/high northern latitudes are quite similar to those observed by radars. The primary nonmigrating tides identified in both the meridional wind and zonal wind semidiurnal spectra at 88 km include the westward propagating wave numbers s = 1 (SW1), 3 (SW3), 4 (SW4), 6 (SW6), the standing s = 0 (S0), and the eastward propagating s = 2 (SE2). The migrating SDT (SW2) amplitude maxima usually occur at 40°N–60°N during December–February and August–September, and also at 40°S–60°S in April–May, with the dominance of (2, 4) during October–April and (2, 3) and (2, 5) dominance for other months. The CMAM-DAS is quite successful in reproducing the dominance of SW1 in the Antarctic summer mesosphere. The modeled SW1 shows very good overall agreement in both amplitude and phase with wind measurements from UARS High Resolution Doppler Imager and Wind Imaging Interferometer (UARS-HRDI/WINDII) and from TIMED Doppler Interferometer (TIDI). The CMAM-DAS analyses for SW3, SW4, SW6, and S0 are also in reasonable agreement with those determined from the HRDI/WINDII or TIDI wind measurements. This work provides further evidence for the tidal forcing from below.

Verification of large-scale rapid transport in the lower thermosphere: Tracking the exhaust plume of STS-107 from launch to the Antarctic

[1] New analysis of the Doppler shift of O2 airglow spectra recorded by the TIMED Doppler Interferometer (TIDI) and the High Resolution Doppler Imager (HRDI) have provided conclusive evidence that the shuttle main engine exhaust plume generated in the lower thermosphere by the launch of STS-107 and imaged by the Global Ultraviolet Imager (GUVI) instrument on TIMED was transported to the Antarctic in ∼80 h, supporting a key inference from the initial study by Stevens et al. (2005). These new results were aided by improved knowledge of the effects of instrumental and satellite artifacts imposed on the Doppler spectra. STS-107 launched on 16 January 2003, and the neutral wind near its launch trajectory and nearby volume was sampled within minutes by TIDI. These initial observations suggested that the northernmost end of the shuttle's exhaust plume would move northeast and that the southern end would move southeast, motions that were identified in imagery acquired during the next orbit of TIMED. The direction and magnitude of plume motion inferred from GUVI images obtained 12, 26, and 50 h after launch were again confirmed by TIDI and HRDI. The appearance of the plume over the Antarctic ∼80 h after launch, inferred from earlier work by the appearance of iron ablated from the shuttle's main engines, was consistent with neutral winds measured by the satellite Doppler instruments over the Antarctic. The transport of the plume from the coast of Florida to the Antarctic was aided by the favorable phase and strong amplitude of a 2 day planetary wave of wave number three in the southern hemisphere on 18 January 2003. The existence of the 2 day wave was deduced from zonally averaged and combined TIDI and HRDI neutral wind observations. We conclude that the existence of strong and sustained winds in the MLT, significantly greater than expected from empirical and theoretical models, is indisputable and provides compelling evidence supporting the global-scale nature of thermospheric winds with magnitude greater than 100 m/s observed by Larsen (2002) from 40 years of sounding rocket chemical release experiments.

Low‐latitude mesospheric mean winds observed by Gadanki mesosphere‐stratosphere‐troposphere (MST) radar and comparison with rocket, High Resolution Doppler Imager (HRDI), and MF radar measurements and HWM93

Low‐latitude mesospheric winds are investigated using data collected from 1995 to 2006 (11 years) by Indian MST radar located at Gadanki (13.5°N, 79.2°E). Clear eastward and westward flow in zonal wind is noticed during solstices and equinoxes, respectively. The meridional wind shows equatorward flow below 75 km and poleward flow above 75 km quite consistent with that observed with other techniques. The winds show a clear semiannual oscillation (SAO) with maxima during equinoxes. The strength of the SAO during spring is larger than that of fall equinox, and the first peak occurs at higher altitudes than the second peak. The observed features are compared with other techniques, namely, rocket, High Resolution Doppler Imager (HRDI), and medium frequency (MF) radar and also with horizontal wind model HWM93. In general, good comparison is seen among various techniques, with some discrepancy observed in amplitudes. Interestingly, decrease in eastward wind with time during winter months is noticed. The significance of the present results lies in showing the consistency/inconsistency of various experimental techniques to measure the middle atmospheric winds, which are very important to assess the climate variability.

TIMED Doppler Interferometer: Overview and recent results

The Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics (TIMED) satellite carries a limb‐scanning Fabry‐Perot interferometer designed to perform remote‐sensing measurements of upper atmosphere winds and temperatures globally. This instrument is called the TIMED Doppler Interferometer, or TIDI. This paper provides an overview of the TIDI instrument design, on‐orbit performance, operational modes, data processing and inversion procedures, and a summary of wind results to date. Daytime and nighttime neutral winds in the mesosphere and lower thermosphere/ionosphere (MLTI) are measured on TIDI using four individual scanning telescopes that collect light from various upper atmosphere airglow layers on both the cold and warm sides of the high‐inclination TIMED spacecraft. The light is spectrally analyzed using an ultrastable plane etalon Fabry‐Perot system with sufficient spectral resolution to determine the Doppler line characteristics of atomic and molecular emissions emanating from the MLTI. The light from all four telescopes and from an internal calibration field passes through the etalon and is combined on a single image plane detector using a Circle‐to‐Line Interferometer Optic (CLIO). The four geophysical fields provide orthogonal line‐of‐sight measurements to either side of the satellite's path and these are analyzed to produce altitude profiles of vector winds in the MLTI. The TIDI wind measurements presented here are from the molecular oxygen (0‐0) band, covering the altitude region 85–105 km. The unique TIDI design allows for more extended local time coverage of wind structures than previous wind‐measuring instruments from high‐inclination satellites. The TIDI operational performance has been nominal except for two anomalies: (1) higher than expected background white light caused by a low‐level light leak and (2) ice deposition on cold optical surfaces. Both anomalies are well understood and the instrumental modes and data analysis techniques have been adjusted to mitigate their effects on data quality. The analysis techniques used to derive winds are described. The TIDI wind measurements from multiple yaw cycles of TIMED have been used to extract migrating diurnal and semidiurnal tides. The migrating tide results are compared with predictions from the Global Scale Wave Model (GSWM), and results from the Upper Atmospheric Research Satellite, High Resolution Doppler Imager (HRDI) instrument. TIDI wind measurements are also compared with ground‐based meteor radar observations, showing consistent results.

Intra-seasonal Oscillations (ISO) of zonal-mean meridional winds and temperatures as measured by UARS

Abstract. Based on an empirical analysis of measurements with the High Resolution Doppler Imager (HRDI) on the UARS spacecraft in the upper mesosphere (95km), persistent and regular intra-seasonal oscillations (ISO) with periods of about 2 to 4 months have recently been reported in the zonal-mean meridional winds. Similar oscillations have also been discussed independently in a modeling study, and they were attributed to wave-mean-flow interactions. The observed and modeled meridional wind ISOs were largely confined to low latitudes. We report here on an analysis of concurrent UARS temperature measurements, which produces oscillations similar to those seen in the meridional winds. Although the temperature oscillations are observed at lower altitudes (55km), their phase variations with latitude are qualitatively consistent with the inferred properties seen in the meridional winds and thus provide independent evidence for the existence of ISOs in the mesosphere.

Distribution of the Magnetic Flux in Elements of the Magnetic Field in Active Regions

The unsigned magnetic flux content in the flux concentrations of two active regions is calculated by using a set of 248 high-resolution Solar and Heliospheric Observatory Michelson Doppler Imager magnetograms for each active region. Data for flaring active region NOAA 9077 (2000 July 14) and nonflaring active region NOAA 0061 (2002 August 9) were analyzed. We present an algorithm to automatically select and quantify magnetic flux concentrations above a threshold p. Each active region is analyzed using four different values of the threshold p (p = 25, 50, 75, and 100 G). Probability distribution functions and cumulative distribution functions of the magnetic flux were calculated and approximated by the lognormal, exponential, and power-law functions in the range of flux Φ > 1019 Mx. The Kolmogorov-Smirnov test, applied to each of the approximations, showed that the observed distributions are consistent with the lognormal approximation only. Neither exponential nor power-law functions can satisfactorily approximate the observed distributions. The parameters of the lognormal distribution do not depend on the threshold value; however, they are different for the two active regions. For flaring active region 9077, the expectation value of the magnetic flux content is μ = 28.1 × 1018 Mx, and the standard deviation of the lognormal distribution is σ = 79.0 × 1018 Mx. For nonflaring active region NOAA 0061, these values are μ = 23.8 × 1018 and σ = 29.6 × 1018 Mx. The lognormal character of the observed distribution functions suggests that the process of fragmentation dominates over the process of concentration in the formation of the magnetic structure in an active region.

Volumetric flow mapping for microvascular networks by bimodality imaging with light microscope and laser doppler imager

A method was developed to produce a composite image of microvascular networks with grayscales proportional to volumetric flows. Velocities in arterioles and venules were assessed with a high-resolution laser Doppler imager (LDI). The vascular structures were quantified from the micrograph with a computerized vessel detection algorithm. After registering the detected vascular network with the LDI scan, volumetric flows were calculated along the centerlines of the vessels. In vivo data were obtained from the hamster cheek pouch in 6 studies. Flow continuity of the flow map was evaluated by comparing the main flow (Q) with the sum of branch flows (Qs), averaging over the respective vessel segments incident to each bifurcation. The method was reproducible across the 6 studies with the correlation coefficient (r) between Qs and Q ranging from 0.913 to 0.986. In all, over 20,000 flow estimates from 360 vessel segments (24-160 microm in diameter) at 166 bifurcations were analyzed. With flow normalized between 0 and 1, the linear regression yielded: Qs = 1.03 Q + 0.006; r = 0.952, n = 166, P < 0.0005. The bimodality imaging method exploits a large amount of velocity and diameter data, and therefore should be useful for studying heterogeneous flows in the microvasculature.

Climatological lower thermosphere winds as seen by ground-based and space-based instruments

Abstract. Comparisons are made between climatological dynamic fields obtained from ground-based (GB) and space-based (SB) instruments with a view towards identifying SB/GB intercalibration issues for TIMED and other future aeronomy satellite missions. SB measurements are made from the High Resolution Doppler Imager (HRDI) instrument on the Upper Atmosphere Research Satellite (UARS). The GB data originate from meteor radars at Obninsk, (55° N, 37° E), Shigaraki (35° N, 136° E) and Jakarta (6° S, 107° E) and MF spaced-antenna radars at Hawaii (22° N, 160° W), Christmas I. (2° N, 158° W) and Adelaide (35° S, 138° E). We focus on monthly-mean prevailing, diurnal and semidiurnal wind components at 96km, averaged over the 1991-1999 period. We perform space-based (SB) analyses for 90° longitude sectors including the GB sites, as well as for the zonal mean. Taking the monthly prevailing zonal winds from these stations as a whole, on average, SB zonal winds exceed GB determinations by ~63%, whereas meridional winds are in much better agreement. The origin of this discrepancy remains unknown, and should receive high priority in initial GB/SB comparisons during the TIMED mission. We perform detailed comparisons between monthly climatologies from Jakarta and the geographically conjugate sites of Shigaraki and Adelaide, including some analyses of interannual variations. SB prevailing, diurnal and semidiurnal tides exceed those measured over Jakarta by factors, on the average, of the order of 2.0, 1.6, 1.3, respectively, for the eastward wind, although much variability exists. For the meridional component, SB/GB ratios for the diurnal and semidiurnal tide are about 1.6 and 1.7. Prevailing and tidal amplitudes at Adelaide are significantly lower than SB values, whereas similar net differences do not occur at the conjugate Northern Hemisphere location of Shigaraki. Adelaide diurnal phases lag SB phases by several hours, but excellent agreement between the two data sources exists for semidiurnal tidal phases throughout the year. These results are consistent with phase retardation effects in the MF radar technique that are thought to exist above about 90km. Prevailing and tidal amplitudes from Shigaraki track year-to-year variations in SB fields, whereas in the Southern Hemisphere poorer agreement exists. The above hemispheric differences are due in part to MF vs. meteor radar techniques, but zonal asymmetries and day-to-day variability, combined with inadequate sampling, may also be playing a role. Based on these results, some obvious recommendations emerge that are relevant to combined GB/SB studies as part of TIMED and other future aeronomy missions.

Nonmigrating semidiurnal and diurnal tides at 95 km based on wind measurements from the High Resolution Doppler Imager on UARS

For more than a decade, derived results from the High Resolution Doppler Imager (HRDI) on UARS have provided an enormous amount of new and invaluable information on the global variability of atmospheric winds. These and other results have given added impetus to theoretical modeling efforts. Until recent years, the large majority of investigations have focused on migrating tides, and now more results on nonmigrating tides have become available. We provide new results for semidiurnal and diurnal nonmigrating tides based on data from HRDI at 95 km. Much of these results have not been obtained before, and they are substantially different from those that have been previously reported. Our amplitudes are usually significantly larger, with more periodicities in both day of year and latitude than results that have previously appeared in the literature. We also find components (up to longitude wave number 3) that are significant and have not been presented before and that traveling components of larger‐longitude wave numbers 4, 5, and 6 can reach several m/s in amplitude. We compare our results with earlier results based on HRDI measurements and from selected models.

The 2‐day wave during the boreal summer of 1994

The 2‐day wave during the boreal summer of 1994 was observed using stratospheric analyses from the British Met Office and at mesospheric heights using medium‐frequency (MF) radars and the microwave limb sounder (MLS) and high‐resolution Doppler imager (HRDI) satellite instruments. Most of the evidence from our study points to a high latitude source for the boreal 2‐day wave event we observed. We found little evidence for a connection between the 2‐day wave event in the mesosphere and activity at lower altitudes. Instead we contend that the 2‐day wave observed at upper mesospheric heights was excited in‐situ. This event was predominantly zonal wave number 2, was highly localized in time, and the disturbance propagated equatorially from high northern latitudes. At stratopause and lower mesospheric heights the largest 2‐day wave amplitudes were seen at high Southern Hemisphere latitudes (i.e., in the winter hemisphere). However, the austral winter 2‐day wave was trapped and did not penetrate to upper mesospheric heights.

Study on oxygen atmospheric band dayglow: global and seasonal variations deduced from high-resolution Doppler imager observations

The atmospheric band of O 2 mapped by high resolution Doppler imager instrument on board of upper atmospheric research satellite during the years 1992–1998 are analyzed to investigate the diurnal, monthly, seasonal, and latitudinal variations. In the equatorial regions, the emission rates are strongest in the spring and fall equinoxes, carrying a semiannual oscillation mode (SAO), which can be linked with the solar influences. In the mid latitudes, the emission rates are strong only in the winter months, showing an annual oscillation mode. The correlation between the emission rate with mesopause temperature is discussed. The intensity and height of the peak emission rates in the northern hemisphere are slightly different from those of southern hemisphere. Similarly, the ozone at 90 km , taken from halogen occultation experiment data also shows a positive correlation with the emission rates. This suggests a strong link with the photochemically produced O atoms. With a Lomb Scargle harmonic analysis, we show that the emission rate has the strongest 182-day oscillation followed by the annual and seasonal oscillations. The relative amplitude depends on the latitude.

Compilation of wind data for the Upper Atmosphere Research Satellite (UARS) Reference Atmosphere Project

The aim of the UARS (Upper Atmosphere Research Satellite) Reference Atmosphere Project (URAP) is to provide a comprehensive zonal mean reference description of the stratosphere using measurements from instruments on board the UARS. A data set has been produced which describes the monthly zonal mean zonal winds from the surface to the upper mesosphere. Wind measurements from the High Resolution Doppler Imager (HRDI) were combined with results from the Met Office stratospheric data assimilation system. Balanced winds derived from the URAP temperature data set were used to bridge the gap between the stratospheric winds and HRDI mesospheric winds.