Mesosphere-stratosphere-troposphere Research Articles

Diurnal variation in vertical air motion over a tropical station, Gadanki (13.5°N, 79.2°E), and its effect on the estimation of mean vertical air motion

The long‐term measurements of vertical air velocity (w) made with the Indian mesosphere‐stratosphere‐troposphere (MST) radar are used to investigate the diurnal variation of w in different seasons. The effect of the diurnal variation of w and gravity wave variance on the estimation of mean w is also studied. Significant diurnal variation is observed in the vertical air motion at Gadanki with a variation larger than 6 cm s−1. This variation is, in fact, larger than the mean vertical air motion. Downdrafts are observed in the evening hours in the lower troposphere in all the seasons. A large part of this subsidence is due to the bias caused by upward propagating gravity waves, as evidenced by large hourly variance values in evening hours. In the middle and upper troposphere, the diurnal variation is dominated primarily by 12‐h oscillation, which is conspicuously present in all the seasons, albeit with different amplitudes. The 24‐h variance caused primarily by tidal and relatively long period oscillations (>2 h) and mesoscale weather disturbances is almost comparable to the variance due to short‐period gravity waves (<1 h). The variance for periods <1 h shows significant diurnal variation with peak values during afternoon‐evening. It implies that the bias in w should also have such a diurnal cycle, because the bias (downward) is directly proportional to the variance in w. Given that w and the bias sources vary considerably during the course of the day, any estimate of mean w (taken over a season/month) from data pertaining to a particular hour (hours) of the day will represent the mean w of that particular hour, but may not truly represent the seasonal/monthly mean w.

Characteristics of the Tropical Easterly Jet: Long‐term trends and their features during active and break monsoon phases

Using high–vertical resolution Indian mesosphere‐stratosphere‐troposphere (MST) radar and GPS sonde observations from Gadanki (13.5°N, 79.2°E), an attempt has been made for the first time to delineate the characteristics of Indian summer monsoon winds with special emphasis on the Tropical Easterly Jet stream (TEJ), its day‐to‐day, monthly, and interannual variability using observations available for more than a decade (1996–2008). For comparison, data available during 1996–2008 from routine radiosonde observations from nearby India Meteorological Department (IMD) observatory located at Chennai (13.0°N, 80.1°E) and National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP‐NCAR) reanalysis data sets have been considered. Relatively poor vertical resolution data from IMD lead to underestimation of the jet characteristics like jet width, vertical shear above and below the jet, and the wind reversal height. Although reanalysis data sets represented well the spatial variability, they underestimate the peak zonal winds by about 5 m/s when compared to Indian MST radar and GPS sonde observations. Large day‐to‐day variability of TEJ characteristics (peak jet speed, jet height, jet width, zonal wind reversal height, and vertical shear of zonal wind) over Gadanki is noticed. No significant trend is observed in peak jet speed using reanalysis data sets either over Gadanki grid or over jet core region in Indian summer monsoon months. However, MST radar and GPS sonde observations show increasing trend (∼1 m/s/yr) in peak jet speed particularly from the year 2000. Characteristics of the TEJ during active and break phases showed quite different features. Thus, statistics generated using the long‐term database from Indian MST radar and GPS sonde provide valuable information for studying the TEJ characteristics and will be useful to incorporate in the future reanalysis data sets.

A new perspective on MST radar observations of stratospheric intrusions into‐troposphere associated with tropical cyclone

This paper presents the first ever evidence of stratospheric intrusion into troposphere during the passage of tropical cyclone using mesosphere‐stratosphere‐troposphere (MST) radar located at Gadanki (13.5°N, 79.2°E). The most significant and new observation is the enhanced signal‐to‐noise ratio (SNR) of thickness ∼1 km, extended from 16–13 km, when the cyclone is located close to the radar site. Small‐scale turbulence and strong downdraft followed by weak updraft are also observed from spectral‐width and vertical velocity, respectively. Further analysis of global data shows low out‐going long wave radiation (<170 W m−2), low tropopause temperature (<191 K), enhanced potential vorticity (∼1 PVU) in the upper/middle troposphere, and low specific humidity (∼2 × 10−4 kg/kg) at 300 hPa pressure level, occurs over the radar site. These observations clearly indicate the evidence of stratospheric intrusion into troposphere during the passage of tropical cyclone. The results are presented and discussed in the light of present understanding.

High resolution observations of turbulence in the troposphere and lower stratosphere over Gadanki

Abstract. High resolution (150 m) wind measurements from 13–17 July 2004 by Mesosphere-Stratosphere-Troposphere (MST) radar and 15–16 July 2004 by Lower Atmospheric Wind Profiler (LAWP) have been used to study the time variation of turbulence intensity. Layers of higher turbulence are observed in the lower stratosphere on 15–16 July which give rise to mixing in the region. Enhancement in short-period gravity wave activity and turbulent layers are observed after 22:00 LT which could be due to a dry convection event that occurred at that time. The breakdown of the convectively generated high frequency waves seems to have given rise to the turbulence layers. Wind shear is found to be high above the easterly jet, but very poor correlation is observed between square of wind shear and turbulence parameters in the region. The heights of the turbulent layers in the lower stratosphere do not correlate with levels of minimum Richardson number. A monochromatic inertia gravity wave could be identified during 13–17 July 2004. A non-linear interaction between the waves of different scales as proposed by Hines (1992) might also be responsible for the breakdown and generation of turbulence layers.

Polar mesospheric summer echoes at 78°N, 16°E, 2008: First results of the refurbished sounding system (SOUSY) Svalbard radar

The second‐generation sounding system (SOUSY) 53.5‐MHz mesosphere‐stratosphere‐troposphere (MST) radar at 78°N, 16°E on Svalbard has recently completed its inaugural summer, 2008, of polar mesospheric summer echoes (PMSE) observations. Here PMSE observations have been assembled in order to identify dates of the earliest and latest occurrences and how the frequency of PMSE occurrence correlates with dynamics and temperature, which are available from the collocated Nippon/Norway Svalbard Meteor 31‐MHz Radar (NSMR). We find strong correlations between preferred PMSE altitude and low temperature, and between equatorward flow and occurrence rate. Temperature drops cause increases in PMSE occurrence: for the height interval 82–92 km, a drop of around 7 K increases the occurrence, typically by 1–2% d−1 and similarly for a 1 m s−1 increase in equatorward wind. A temperature drop of 5 K at 90 km altitude results in a lowering of the underlying preferred PMSE altitude by 1 km. This study therefore qualifies, at least for 78°N, 16°E and 2008, the dependence of PMSE occurrence rates and preferred heights on 90 km temperature and dynamics.

Lidar studies of particulates in the UTLS region at a tropical station over the Indian subcontinent

Characteristics of particulate matter in the upper troposphere and lower stratosphere (UTLS) region during the volcanic quiescent period of 1998–2003 are studied using dual polarization lidar observations at the tropical station Gadanki (13.5°N, 79.2°E). This study revealed a pronounced summer‐winter contrast of the particulate backscatter coefficient (βa) in the LS region with relatively high values during winter and low values during summer. High values of βa (>10−6 m−1 sr−1) in the UT region during summer are closely associated with the manifestation of semitransparent cirrus clouds in this region. High values of volume depolarization ratio (VDR) exceeding 0.04 and increasing up to 0.6 usually encountered in the UT region during this period could be due to the presence of relatively large nonspherical ice particles. These values in the LS region, which are relatively small (<0.04), indicate that the particles in this region are relatively small and more or less spherical in nature. The present study shows that convective activity prevailing in the troposphere significantly influences the microphysical properties of particulates in the UTLS region. Convective available potential energy and outgoing longwave radiation, which are good representative indices for tropospheric convection, show good correlation with VDR in the lower stratosphere during summer and weak correlation during winter. The role of vertical transport from troposphere to stratosphere is also investigated using the vertical wind obtained from mesosphere‐stratosphere‐troposphere (MST) radar data. This study shows that the seasonal variation of mean backscatter coefficient matches well with the corresponding variation in mean vertical mass flux. These results suggest that highly nonspherical particles associated with cirrus clouds forming in the upper troposphere and subsequent uplift across the tropopause aided by strong convection in the troposphere during the summer monsoon period are responsible for the increased VDR observed in the upper troposphere and lower stratosphere region, while the transport of air from troposphere to stratosphere, which is more pronounced during winter, is responsible for the increase in backscatter coefficient in the lower stratosphere.

Gravity wave characteristics observed over a tropical station using high‐resolution GPS radiosonde soundings

Several investigations of the dominant period gravity waves (GWs) were conducted earlier using Indian mesosphere‐stratosphere‐troposphere (MST) radar located at Gadanki (13.5°N, 79.2°E). However, these works had their own limitations of unavailability of continuous data, low SNR, and lack of reliable data at the stratospheric heights (in the case of MST radar) and low spatial resolution (for routine balloon data). For the present study, high‐resolution GPS radiosonde data for more than 2 years (2006–2008) has been used for the first time to characterize the dominant GWs and their associated source mechanisms. Particular attention is paid (1) to check the consistency in GW characteristics observed with MST radar, (2) to estimate potential energy, kinetic energy, and hence total energy, (3) to extend the analysis up to 25 km and check whether vertical wavelength is the same as that observed by MST radar in the lower stratosphere, and finally (4) to estimate the exact direction of propagation in horizontal, which was not possible from MST radar alone. Clear semiannual variation in GW energy, with maximum during monsoon and winter and minimum during premonsoon and postmonsoon in the troposphere, is noticed during 2006 but not clear in 2007. Annual variation is observed in the lower stratosphere with maximum during monsoon (winter enhancement is not significant) season. Strong eastward shear due to tropical easterly jet and orography is found to be responsible for generating the GWs during the monsoon and winter, respectively. Although several features are consistent with that observed earlier, a few new features have been observed by GPS radiosonde and are reported in the present study.

Characteristics of Vertical Velocity Cores in Different Convective Systems Observed over Gadanki, India

Abstract The Indian mesosphere–stratosphere–troposphere (MST) radar measurements during the passage of 60 convective systems are used to study the vertical air velocity (w) characteristics of tropical convection. The up- and downdraft cores and various stages/types of convection (shallow, deep, and decaying) are discerned from radar time–intensity maps of w. The characteristics of cores (speed, size, orientation, vertical extent, gravity wave activity, etc.) at different stages of convection are discussed with the help of three case studies. The cores stratified based on the type of convection are mostly erect in nature in all types of convective systems, except for deep updraft cores. A considerable percentage (35%) of deep updraft cores show inclined structure with elevation angles as low as 0°–20°. The variation of the horizontal wind field with height and the internal dynamics of mesoscale convective systems (MCSs) are thought to be responsible for this geometry. Further, the vertical extent of draft cores is limited in all types of convection, except for deep updraft cores. About 77% of deep updraft cores have a vertical extent greater than 10 km and ∼23% of these cores reach an altitude of 16 km. The size (overpass time) of the core shows an increasing trend with altitude up to 10–12 km and then decreases. Among different types of convection, the size of core is larger for deep updraft cores and smaller for shallow updraft cores. The variation of w distribution with height is different for different convection categories. The mode (and also the mean) of the distribution shows low-level descent (below 3 km) and mid–high-level ascent in shallow and deep convection categories, while nearly uniform distribution is seen in decaying convection. Strong updrafts are seen in deep convective systems in the upper troposphere (of the order of 15–20 m s−1), followed by shallow and decaying systems, while downdrafts are generally weaker in all types of convection. The variability (within the cores and also with altitude) and the number of data points are larger in updraft cores than in downdraft cores corresponding to shallow and deep convection. Contrasting the composite w profile at Gadanki with those obtained elsewhere revealed interesting features: the absence of subsidence at higher levels, the presence of low-level subsidence, a single ascent peak in the middle troposphere, etc. Further, the magnitude of composite w derived from wind profiler measurements is larger than that obtained with other techniques.

Multipeak Raindrop Size Distribution Observed by UHF/VHF Wind Profilers during the Passage of a Mesoscale Convective System

Abstract The Indian Mesosphere–Stratosphere–Troposphere radar (IMSTR), Lower Atmospheric Wind Profiler (LAWP), and Joss–Waldvogel (JW) disdrometer measurements during the passage of two distinctly different (in terms of total rain and rainfall rate) convective storms are utilized to understand the nature and origin of the multipeak raindrop size distribution (MRDSD). Important issues, such as the preferential stage and height at which bi- or multimodal rain distribution occurs in a mesoscale convective system (MCS) are addressed. For both of the storms, the MRDSD is observed during the transition period from convection to stratiform rain. The pattern and variation of the MRDSD during this period is strikingly similar in both of the storms. The MRDSD is first observed above the freezing level in the presence of heavy riming. The subsequent spectra have shown bimodal distribution below the freezing level, and the bimodality is attributed to the coexistence of ice and supercooled droplets. Interestingly, the bimodal distribution has not varied much with altitude when it is produced because of the coexistence of ice and supercooled droplets. The MRDSD is also observed at few range gates and for a short duration. Such a type of MRDSD is seen during the transition period between decaying and intensifying rain.

Evaluation of DBS Wind Measurement Technique in Different Beam Configurations for a VHF Wind Profiler

Abstract Atmospheric winds in the troposphere have been observed routinely for many years with wind profiling (VHF and UHF) radars using the Doppler beam swinging (DBS) technique. Accuracy of wind estimates using wind profiling radars with different beam configurations has its limitations due to both the system of observation and atmospheric conditions. This paper presents a quantitative analysis and evaluation of horizontal wind estimation in different beam configurations up to an altitude of 18 km using the mesosphere–stratosphere–troposphere (MST) radar located in Gadanki, India. Horizontal wind velocities are derived in three different ways using two-, three-, and four-beam configurations. To know the performance of each configuration, radar-derived winds have been compared with the winds obtained by simultaneous GPS sonde balloon measurements, which are considered to be a standard reference by default. Results show that horizontal winds measured using three different beam configurations are comparable in general but discrepancy varies from one beam configuration to the other. It is observed that horizontal winds measured using four-beam configuration (east, west, north, and south) have better estimates than the other two-beam configurations. The standard deviation was found to be varying from 1.4 to 2.5 m s−1 and percentage error is about 9.68%–12.73% in four-beam configuration, whereas in other beam configurations the standard deviation is about 1.65–3.9 m s−1 and the percentage error is about 11.29%–15.16% with reference to GPS sonde balloon–measured winds.

Inter-hemispheric asymmetry in polar mesosphere summer echoes and temperature at 69° latitude

An inter-hemispheric asymmetry is found in the characteristics of polar mesosphere summer echoes (PMSE) and upper mesosphere temperatures at conjugate latitudes (∼69°) above Antarctica and the Arctic. The second complete mesosphere–stratosphere–troposphere (MST) radar summer observation season at Davis (68.6°S) revealed that PMSE occur less frequently, with lower strength and on average 1 km higher compared with their northern counterparts at Andenes (69.3°N). We consider the thermodynamic state of the mesosphere for conjoining hemispheric summers based on satellite and ground-based radar measurements, and show the mesopause region near ∼80–87 km of the Southern Hemisphere (SH) to be up to 7.5 K warmer than its Northern Hemisphere (NH) counterpart. We show that this is consistent with our observation of asymmetries in the characteristics of PMSE and demonstrate how the mesosphere meridional wind field influences the existence and strength of the echoes in both hemispheres.

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.

A Study on Optimum Tilt Angle for Wind Estimation Using Indian MST Radar

Abstract The effect of tilt angle on horizontal wind estimation is studied using Indian mesosphere–stratosphere–troposphere (MST) radar located at Gadanki (13.45°N, 79.18°E). It operates in Doppler beam swinging (DBS) mode with a beamwidth of 3°. Horizontal winds are computed for different tilt angles from 3° to 15° with an increment of 3° from a height range of 3.6–18 km. The effective beam pointing angle (θeff) is calculated to determine the effect of aspect sensitivity on the determination of horizontal wind components. For different tilt angles radar-derived winds are compared with simultaneous GPS sonde wind measurements, which were launched from a nearby site. The first method utilizes direct comparison of radar-derived winds with those of GPS sondes using the actual beam pointing angle; the second method uses the effective beam pointing angle derived from the ratios of two oblique beams. For this study a variety of statistics were explored in terms of standard deviation, correlation coefficient, and percentage error. From the results it is observed that in agreement with previous studies, the effective beam pointing angle deviates from the actual beam pointing angle, which results in the underestimation of horizontal wind components, and also when tilt angle is close to zenith and far from zenith, the estimation of horizontal winds is found to be far from true values at different heights. Radar wind estimation has better agreement with GPS sonde measurement when the off-zenith angle is around 10°. It is also found that correction to the actual beam pointing angle provides 3%–6% improved agreement between the radar and GPS wind measurements.

Long-term MST radar observations of vertical wave number spectra of gravity waves in the tropical troposphere over Gadanki (13.5° N, 79.2° E): comparison with model spectra

Abstract. The potential utility of Mesosphere-Stratosphere-Troposphere (MST) radar measurements of zonal, meridional and vertical winds for divulging the gravity wave vertical wave number spectra is discussed. The data collected during the years 1995–2004 are used to obtain the mean vertical wave number spectra of gravity wave kinetic energy in the tropical troposphere over Gadanki (13.5° N, 79.2° E). First, the climatology of 3-dimensional wind components is developed using ten years of radar observations, for the first time, over this latitude. This climatology brought out the salient features of background tropospheric winds over Gadanki. Further, using the second order polynomial fit as background, the day-to-day wind anomalies are estimated. These wind anomalies in the 4–14 km height regions are used to estimate the profiles of zonal, meridional and vertical kinetic energy per unit mass, which are then used to estimate the height profile of total kinetic energy. Finally, the height profiles of total kinetic energy are subjected to Fourier analysis to obtain the monthly mean vertical wave number spectra of gravity wave kinetic energy. The monthly mean vertical wave number spectra are then compared with a saturation spectrum predicted by gravity wave saturation theory. A slope of 5/3 is used for the model gravity wave spectrum estimation. In general, the agreement is good during all the months. However, it is noticed that the model spectrum overestimates the PSD at lower vertical wave numbers and underestimates it at higher vertical wave numbers, which is consistently observed during all the months. The observed discrepancies are attributed to the differences in the slopes of theoretical and observed gravity wave spectra. The slopes of the observed vertical wave number spectra are estimated and compared with the model spectrum slope, which are in good agreement. The estimated slopes of the observed monthly vertical wave number spectra are in the range of −2 to −2.8. The significance of the present study lies in using the ten years of data to estimate the monthly mean vertical wave number spectra of gravity waves, which will find their application in representing the realistic gravity wave characteristics in atmospheric models.

MST radar and radiosonde observations of inertia‐gravity wave climatology over tropical stations: Source mechanisms

In this paper, possible source mechanisms for the generation of inertia‐gravity wave activity over a tropical station, Gadanki (13.5°N, 79.2°E), are investigated using a long‐term data set obtained from Indian mesosphere‐stratosphere‐troposphere (MST) radar. The gravity wave analysis is carried out in two different height regions, namely, 4–14 and 17–21 km, representing the troposphere and lower stratosphere, respectively. Clear seasonal variation in the wave activity has been noticed in both regions with maximum (minimum) in winter (monsoon) in the troposphere. But it is maximum (minimum) in monsoon (winter) in the lower stratosphere. This kind of winter enhancement in the wave activity is not expected at this tropical site. Interestingly, the contribution of the meridional component to the total kinetic energy (Ek) is found to be dominant rather than zonal in the winter except during 1997–1998. Topography seems to be the likely source for the generation of wave activity during winter in the troposphere. The influence of this topography is also reflected in the nearby radiosonde stations, Chennai (13.0°N, 80.2°E) and Bangalore (12.9°N, 77.6°E), which are located at radial distances of 128 and 190 km from Gadanki, respectively. Although two major sources, that is, strong convection and wind shears, coexist during monsoon season, strong wind shear seems to be the likely source of the wave activity. Large interannual variability in the wave activity is also noticed from 9 years (September 1995 to December 2004) of data. Good consistency is observed between the wave activities observed from nearby (Chennai) radiosonde and Gadanki MST radar data sets. Making use of a network of radiosonde observations operated by India Meteorological Department, we also present the latitudinal variation of wave activity. From the latitudinal variations it is observed that large‐scale systems can also influence the generation of the gravity wave activity over larger areas.

Analysis of convectively‐generated gravity waves in mesoscale model simulations and wind‐profiler observations

AbstractThe characteristics of convectively‐generated gravity waves during an episode of deep convection near the coast of Wales are examined, in high‐resolution mesoscale simulations with the Met Office Unified Model and in observations from a mesosphere–stratosphere–troposphere wind‐profiling Doppler radar. In this episode, deep convection reached the tropopause and generated vertically‐propagating high‐frequency waves in the lower stratosphere that produced vertical‐velocity perturbations of order of 1 ms−1. Wavelet analysis is applied in order to determine the characteristic periods and wavelengths of the waves. Both in the simulations and in the observations, the wavelet spectra contain several distinct preferred scales, indicated by multiple spectral peaks. The peaks are most pronounced in the horizontal spectra at several wavelengths less than 50 km. Although these peaks are most clear, and of largest amplitude, in the highest‐resolution simulations (with 1 km horizontal grid length), they are also evident in coarser simulations (with 4 km horizontal grid length). Peaks also exist in the vertical and temporal spectra (at approximately 2.5–4.5 km and 10–30 min respectively), with good agreement between simulation and observation. Two‐dimensional (wave‐number–frequency) spectra demonstrate that each of the selected horizontal scales contains peaks at each of the preferred temporal scales revealed by the one‐dimensional spectra alone. Copyright © 2008 Royal Meteorological Society

Simulation of microphysical structure associated with tropical cloud clusters using mesoscale model and comparison with TRMM observations

An attempt has been made in the present study to examine the microphysical structure of a non‐squall Tropical Cloud Cluster (TCC). Three‐dimensional model simulations of cloud microphysical structure associated with a non‐squall TCC occurred on 26 October 2005 over the South Bay of Bengal have been carried out. The initial conditions for the model simulations were improved by incorporating upper air radiosonde observations and Indian Mesosphere Stratosphere Troposphere (MST) radar wind observations through analysis nudging. The horizontal and vertical distribution of the cloud hydrometeor fields observed from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) are compared to those simulated by a mesoscale model using a sophisticated microphysical scheme. Substantial differences are noticed in the amounts of cloud microphysical parameters, with simulated values of hydrometeors being higher than TMI retrievals. Spatial distribution of Cloud Liquid Water (CLW) and Rain Water (RNW) from TMI and model simulations correspond well with each other. The cloud microphysical structure during the initial and mature phases of the storm is also investigated. Comparisons of horizontal and vertical reflectivity structure from the TRMM‐Precipitation Radar (PR) and those simulated by the model show reflectivity cores of values greater than 30 dBZ. The TRMM‐PR echo tops are 3–4 km higher than the simulated echo tops. The 24 hr accumulated precipitation from model simulations are then verified with the combined rainfall product from the TRMM observations.

Anomalous Wind Circulation Observed during 1997/98 El Niño Using Indian MST Radar

Abstract Unique facility of measuring vertical winds using Indian mesosphere–stratosphere–troposphere (MST) radar along with horizontal winds enables the study of the atmospheric circulation over Gadanki, India. Several important features are noted while analyzing the wind field. A tropical easterly jet stream of 35 m s−1 strength is seen around 16 km during monsoon season. Relatively strong jetlike northward motion (southerlies) of 5–7 m s−1 is seen around 14 km during winter months. These two maxima in zonal and meridional wind patterns, even though they differ in strength greatly, occur in two contrasting seasons. Downward motion combined with upper-level northward and lower-level southward motion observed during winter in normal years indicates the signature of tropical Hadley circulation over the study region. During the 1997/98 El Niño event, however, an anomalous pattern of winds is seen and Hadley circulation is observed to be weakened.

Meteor observations using the Davis mesosphere‐stratosphere‐troposphere radar

The Davis mesosphere‐stratosphere‐troposphere (MST) radar (69°S, 78°E) was installed in February 2003. Although the primary interest is the observation of polar mesosphere summer echoes, external transmit and receive antennas were installed to allow all‐sky interferometric meteor radar observations. This paper presents the first results from the meteor observations. The annual count rate variation shows good agreement with previous high‐latitude observations, peaking in midsummer and minimizing in early spring. The height distribution shows significant annual variation, with minimum (maximum) peak heights and maximum (minimum) widths observed in early spring (midsummer). Radiant mapping has been used to identify the Southern delta‐Aquarid Sagittariid and July Phoenicid meteor showers, and to investigate sources of sporadic meteors. Winds and temperatures derived from the meteor observations are also presented, showing good agreement with independent colocated measurements. There is some indication that the winds below the peak height of the meteor height distribution are smeared to lower heights, which may be indicative of a previously undocumented bias in meteor wind estimates.

Wind characteristics of the troposphere and lower stratosphere during the passage of a tropical cyclone over India using VHF radar

A tropical depression formed in the west central Bay of Bengal on 15th October 2001 intensified into a cyclonic storm and crossed over the Indian mesosphere–stratosphere–troposphere (MST) Radar site at Gadanki (13.5°N, 79.2°E), India on the next day morning. Three-dimensional wind characteristics of the troposphere and lower stratosphere have been studied based on the continuous observations using MST radar at Gadanki during 15–16 October 2001. Horizontal wind components in the upper troposphere and lower stratosphere showed an abrupt increase during the passage of the storm, whereas the wind changed its direction and became very weak in lower levels (4–8 km). The observed vertical velocity was very high in the level of maximum convective outflow (10–12 km). After the passage of the cyclonic storm upper and lower tropospheric wind speed reduced considerably, whereas the mid-tropospheric wind speed increased.