Mesosphere-stratosphere-troposphere Research Articles

Evaluation of the Horizontal Winds Simulated by IAP-HAGCM through Comparison with Beijing MST Radar Observations

The performance of general circulation models (GCMs) in simulating horizontal winds is important because the distribution and variation in horizontal winds are central to investigating atmospheric dynamic characteristics and processes. Also, horizontal wind data can be used to extract some of the required information on gravity waves, tides, and planetary waves. In this context, the present paper evaluates the capability of the Institute of Atmospheric Physics atmospheric general circulation model high-top version (IAP-HAGCM) in simulating the horizontal winds and tides of the troposphere and lower stratosphere by presenting a climatological and statistical comparison against observations of the powerful Beijing mesosphere–stratosphere–troposphere (MST) radar (39.78°N, 116.95°E) during 2012–2014. The results illustrated that the IAP-HAGCM can successfully reproduce the time–altitude distribution of the monthly mean zonal wind and diurnal tide amplitude, albeit with some underestimation. The mean correlation coefficients and root-mean-square error for the zonal (meridional) winds were 0.94 (0.73) and 6.60 m s−1 (2.90 m s–1), respectively. Additionally, the IAP-HAGCM can capture the temporal variation in both the zonal and meridional winds. It is worth noting that, compared with the seven coupled model intercomparison project phase 6 (CMIP6) models, the IAP-HAGCM performs better in meridional wind simulations below 15 km. However, there are discrepancies in altitudinal ranges with large wind velocities, such as the westerly jet, in the transition region of the troposphere and stratosphere, and in February, April, July, and September. It is suggested that model users should take advantage of the model’s simulation ability by combining this information regarding when and where it is optimal with their own research purposes. Moreover, the evaluation results in this paper can also serve as a reference for guiding improvements of the IAP-HAGCM.

Middle atmospheric structure, dynamics, and coupling from three decades of Indian MST radar and complimentary observations: An overview

The genesis for Indian Mesosphere-Stratosphere-Troposphere (MST) radar came from the Indian Middle Atmospheric Programme (IMAP) to study the middle atmospheric dynamics and its underlying processes. During the early 1990s VHF radar operating at 53 MHz has been set up at Gadanki (13.5°N, 79.2°E), India, which started operating initially in the stratospheric and tropospheric (ST) mode. It is upgraded to MST mode in 1993. Since then, it has served various scientific experiments not only from India but under international collaboration. Numerous focused campaigns that have national and international importance were conducted. Using this unique data in the last 30 years along with complementary measurements, several stimulating results has been reported covering a wide range of topics that includes gravity wave characteristics, tides, planetary waves, oscillations, tropopause dynamics and stratosphere-troposphere exchange processes, monsoon dynamics and circulations, mesospheric structure and dynamics, vertical and lateral coupling and long-term trends. The present communication will highlight the unique results obtained using long-term observations of Indian MST radar and complementary techniques covering the complete middle atmosphere. Unique results include quantification of the momentum carried by the high-frequency waves generated in the troposphere up to the mesosphere, demarcating the complete tropical tropopause layer using MST radar observations alone, indication for the strengthening of the tropical easterly jet in the recent decade, unusual behavior of the Hadley circulation during drought and El Nino years, the revelation of the mechanisms for the occurrence of mesospheric echoes at the tropical latitudes, quantification of the turbulence, evidence for the role of anthropogenic changes on the dynamics of the mesosphere and generation of the empirical model by combing multi-instrument data sets. These data set also served in validating numerous ground-based and space-borne measurements including several re-analysis products over a tropical latitude. Issues remained unresolved and ways to tackle in future experiments are highlighted.

Mid‐Latitude Mesospheric Responses of the Solar Eclipse on 21 June 2020 Observed by the Wuhan MST Radar

AbstractAn annular solar eclipse shifted across the earth from the middle of Africa to the Pacific on 21 June 2020. The Wuhan Mesosphere‐Stratosphere‐Troposphere (MST) radar was located on the eclipse path to provide us a rare opportunity to investigate the atmospheric responses to the rapid variation of solar radiations. The east, north, and vertical beams of the Wuhan MST radar were applied to record the echoes from mesosphere with 10 min sampling period. A Digisonde located near the MST radar was also used to investigate the variations of ionospheric Es layer during the solar eclipse. The mesosphere region between 70 and 80 km heights presented obvious responses to the eclipse. The echoes disappeared at around the eclipse maximum, indicating the dominant role of the solar radiation. The descending and ascending echo structures were recorded in the first and recovery phases of the eclipse, respectively. The Digisonde also found the evidence of the eclipse induced gravity waves in the Es layer that just above the mesosphere. The lunar shadow produced southward winds on the northside of the eclipse path is considered to induce the descending echo structure. The upward propagating gravity waves generated during the eclipse may be responsible for the ascending echo structure.

Wuhan MST Radar Observations of a Tropopause Descent Event during Heavy Rain on 1–2 June 2015

During heavy rain on 1–2 June 2015 in central China, the Wuhan mesosphere–stratosphere–troposphere (MST) radar was applied to record the atmospheric responses to the rain with a 30 min period. According to the vertical gradient of the echo power above 500 hPa, the tropopause height could be determined by MST radar detection. The tropopause descent was clearly observed by the Wuhan MST radar a few hours before the rain, and then the tropopause recovered to usual heights during the rain. The observation of the radiosonde in Wuhan was in line with that of the radar. Both the potential vorticity and the ozone mass mixing ratio variations at 100 hPa level implied the fall of the tropopause. During the tropopause decent, enhanced radar echoes appeared in the upper troposphere, the echo spectral widths became broader, and the large vertical wind velocities were recorded and indicated the occurrence of strong convective activities. The relative humidity was also found to increase at all tropospheric heights, including the region close to the tropopause. The convective flow may have transported water vapor to the tropopause heights, and a temperature decrease in this region was also recorded. It is very likely that water vapor cooling induced the tropopause descent.

Turbulence parameters measured by the Beijing mesosphere–stratosphere–troposphere radar in the troposphere and lower stratosphere with three models: comparison and analyses

Abstract. Based on the quality-controlled observational spectral width data of the Beijing mesosphere–stratosphere–troposphere (MST) radar in the altitudinal range of 3–19.8 km from 2012 to 2014, this paper analyses the relationship between the proportion of negative turbulent kinetic energy (N-TKE) and the horizontal wind speed and the vertical shear of horizontal wind domain and gives the distributional characteristics of atmospheric turbulence parameters obtained by using different calculation models. Three calculation models of the spectral width method were used in this study – namely the H model (Hocking, 1985), N-2D model (Nastrom, 1997) and D–H model (Dehghan and Hocking, 2011). The results showed that the proportion of N-TKE in the H model, N-2D model and D–H model increases with the horizontal wind speed u and/or the vertical shear of horizontal wind speed ∂u∂z, and the maximum values are 60 %, 45 % and 35 %, respectively. When the∂u∂z is greater than 0.006 s−1, the N-TKE of the H model increases sharply with ∂u∂z; the increase rate is about 20%0.002s-1. For these three models, the results are similar except that the vertical shear of the horizontal wind speed is greater than 0.006 s−1. When ∂u∂z>0.006 s−1, the proportion of N-TKE in the N-2D and H models increases with ∂u∂z, while the proportion in the D–H model is less than 10 % and has slight variation. However, it is still necessary to consider the applicability of the N-2D model and D–H model in some weather processes with strong winds. The distributional characteristics with height of the turbulent kinetic energy dissipation rate ε and the vertical eddy diffusion coefficient Kz derived by the three models are consistent with previous studies. Still, there are differences in the values of turbulence parameters. Also, the range resolution of the radar has little effect on the differences in the range of turbulence parameters' values. The median values of ε in the H model, N-2D model and D–H model is 10−3.2–10−2.7, 10−3.0–10−2.6 and 10−3.3–10−2.8 m2 s−3, respectively. The median values of Kz in these three models are 100.3–100.7, 100.4–100.7 and 100.1–100.5 m2 s−1.

Volume imaging of aspect sensitivity in VHF radar backscatters: first results inferred from the Advanced Indian MST radar (AIR)

ABSTRACT Very-high frequency (VHF) radar echoes are known to be aspect sensitive in general, which could be either the manifestation of a thin stable layer providing sharp refractive index gradient or shear-driven steep layer structures. The present study for the first time shows the volume imaging of aspect sensitivity in the recently upgraded Advanced Indian Mesosphere Stratosphere Troposphere (MST) radar (AIR). The present configuration of radar can provide a better understanding of three-dimensional structures of turbulence and instabilities, which was not possible when the radar was operated in two orthogonal planes. Both isotropic and anisotropic layers/turbulence are observed at various height levels over the radar volume. Enhanced aspect sensitivity is observed between 6 and 9 km, which is attributed to the presence of dynamic instability arising due to strong wind shear and atmospheric stability. All the scatterers tend to become isotropic when both the square of wind shear and stability parameters are above 0.25 × 10−3 s−2. Due to the high aspect sensitivity, there may be an underestimate of 5–10% in wind velocity measurements, and it is higher for the low off-zenith beam angle.

Meteor radar observations of polar mesospheric summer echoes over Svalbard

Abstract. A 31 MHz meteor radar located in Svalbard was used to observe polar mesospheric echoes (PMSEs) during summer 2020. Data from 19 July were selected for detailed analysis, with a focus on extracting additional information to characterize the atmosphere in the PMSE region. The use of an all-sky meteor radar adds an additional use to data collected for meteor observations and enables the detection of PMSE layers across a wide field of view. Comparison with data from a 53.5 MHz narrow-beam mesosphere–stratosphere–troposphere (MST) radar shows good agreement in the morphology of the layer as detected between the two systems. Doppler spectra of PMSE layers reveal fine structure, including regions of enhanced return that move across the radar's field of view. Examination of the relationship between range and Doppler shift of off-zenith portions of the layer enables the estimation of wind speeds with high temporal resolution during PMSE conditions. Trials demonstrate good agreement between wind speeds obtained from PMSE Doppler spectra and those calculated from specular meteor trail radial velocities. Combined with the antenna polar diagram of the radar, this same relationship was used to infer the aspect sensitivity of observed PMSE backscatter, yielding a mean backscatter angular width of 6.8±3.3∘. A comparison of underdense meteor radar echo decay times during and outside of PMSE conditions did not demonstrate a strong correlation between the presence of PMSEs and shortened underdense meteor radar echo durations.

Ozone vertical distribution during the solar eclipse of 26 December 2019 over Gadanki: Role of background dynamics

A multi-instrument campaign was conducted to investigate the changes in ozone vertical distribution during the annular solar eclipse that occurred in the morning hours (08:10 to 11:15 Indian Standard Time) on 26 December 2019 using both in-situ and remote sensing observations over Gadanki (13.5oN,79.2oE), India. A series of ozonesondes were launched before and after the solar eclipse along with continuous observations from the Brewer MKIII spectrophotometer and Mesosphere-Stratosphere-Troposphere (MST) radar. An enhancement (~30–60 ppbv) in upper tropospheric (10–18 km) ozone was observed immediately after the solar eclipse along with a reduction in the total ozone by 20 DU, at the maximum of solar obscuration. The MST radar observations and interpretation of meteorological reanalysis data and backward trajectory simulations suggest that this ozone enhancement was due to a downdraft from the stratosphere which began a few hours before the eclipse, as well as long-range transport associated with the sub-tropical jet. A mid-tropospheric (4–10 km) ozone enhancement which also occurred during the eclipse was also produced by the action of the sub-tropical jet. However, the cold point tropopause was significantly lower in height at the maximum of the eclipse, and this region subsequently warmed over a period of several hours. The observations during this event further highlight that background dynamics need to be taken into consideration when evaluating the atmospheric effects of different solar eclipses at tropical latitudes.

Validation of wind measurements of two mesosphere–stratosphere–troposphere radars in northern Sweden and in Antarctica

Abstract. Two atmospheric VHF radars: ESRAD (Esrange MST radar) located near Kiruna in the Swedish Arctic and MARA (Moveable Atmospheric Radar for Antarctica) at the Indian research station Maitri in Antarctica perform wind measurements in the troposphere and lower stratosphere on a regular basis. We compared horizontal winds at altitudes between about 0.5 and 14 km derived from the radar data using the full correlation analysis (FCA) technique with radiosonde observations and models. The comparison with 28 radiosondes launched from January 2017 to August 2019 showed that ESRAD underestimates the zonal and meridional winds by about 8 % and 25 %, respectively. This is likely caused by the receiver group arrangement used for the FCA together with a high level of non-white noise. A similar result was found when comparing with the regional numerical weather prediction model HARMONIE-AROME (Bengtsson et al., 2017) for the period September 2018–May 2019. The MARA winds were compared with winds from radiosondes for the period February–October 2014 (291 occasions). In contrast to ESRAD, there is no indication that MARA underestimates the winds compared to the sondes. The mean difference between the radar and radiosonde winds is close to zero for both zonal and meridional components. The comparison of MARA with the ECMWF ERA5 reanalysis for January–December 2019 reveals good agreement with the mean difference between 0.1 and −0.5 m/s depending on the component and season. The random errors in the wind components (standard deviations over all estimates in 1 h averages) are typically 2–3 m/s for both radars. Standard deviation of the differences between radars and sondes are 3–5 m/s.

Probabilistic analysis of ambiguities in radar echo direction of arrival from meteors

Abstract. Meteors and hard targets produce coherent radar echoes. If measured with an interferometric radar system, these echoes can be used to determine the position of the target through finding the direction of arrival (DOA) of the incoming echo onto the radar. Depending on the spatial configuration of radar-receiving antennas and their individual gain patterns, there may be an ambiguity problem when determining the DOA of an echo. Radars that are theoretically ambiguity-free are known to still have ambiguities that depend on the total radar signal-to-noise ratio (SNR). In this study, we investigate robust methods which are easy to implement to determine the effect of ambiguities on any hard target DOA determination by interferometric radar systems. We apply these methods specifically to simulate four different radar systems measuring meteor head and trail echoes, using the multiple signal classification (MUSIC) DOA determination algorithm. The four radar systems are the Middle And Upper Atmosphere (MU) radar in Japan, a generic Jones 2.5λ specular meteor trail radar configuration, the Middle Atmosphere Alomar Radar System (MAARSY) radar in Norway and the Program of the Antarctic Syowa Mesosphere Stratosphere Troposphere Incoherent Scatter (PANSY) radar in the Antarctic. We also examined a slightly perturbed Jones 2.5λ configuration used as a meteor trail echo receiver for the PANSY radar. All the results are derived from simulations, and their purpose is to grant understanding of the behaviour of DOA determination. General results are as follows: there may be a region of SNRs where ambiguities are relevant; Monte Carlo simulation determines this region and if it exists; the MUSIC function peak value is directly correlated with the ambiguous region; a Bayesian method is presented that may be able to analyse echoes from this region; the DOA of echoes with SNRs larger than this region are perfectly determined; the DOA of echoes with SNRs smaller than this region completely fail to be determined; the location of this region is shifted based on the total SNR versus the channel SNR in the direction of the target; and asymmetric subgroups can cause ambiguities, even for ambiguity-free radars. For a DOA located at the zenith, the end of the ambiguous region is located at 17 dB SNR for the MU radar and 3 dB SNR for the PANSY radar. The Jones radars are usually used to measure specular trail echoes far from zenith. The ambiguous region for a DOA at 75.5∘ elevation and 0∘ azimuth ends at 12 dB SNR. Using the Bayesian method, it may be possible to analyse echoes down to 4 dB SNR for the Jones configuration when given enough data points from the same target. The PANSY meteor trail echo receiver did not deviate significantly from the generic Jones configuration. The MAARSY radar could not resolve arbitrary DOAs sufficiently well enough to determine a stable region. However, if the DOA search is restricted to 70∘ elevation or above by assumption, stable DOA determination occurs above 15 dB SNR.

Wuhan MST radar: technical features and validation of wind observations

Abstract. The Wuhan mesosphere–stratosphere–troposphere (MST) radar is a 53.8 MHz monostatic Doppler radar, located in Chongyang, Hubei Province, China, and has the capability to observe the dynamics of the mesosphere–stratosphere–troposphere region in the subtropical latitudes. The radar system has an antenna array of 576 Yagi antennas, and the maximum peak power is 172 kW. The Wuhan MST radar is efficient and cost-effective and employs more simplified and more flexible architecture. It includes 24 big transmitter–receiver (TR) modules, and the row or column data port of each big TR module connects 24 small TR modules via the corresponding row or column feeding network. Each antenna is driven by a small TR module with peak output power of 300 W. The arrangement of the antenna field, the functions of the timing signals, the structure of the TR modules, and the clutter suppression procedure are described in detail in this paper. We compared the MST radar observation results with other instruments and related models in the whole MST region for validation. Firstly, we made a comparison of the horizontal winds in the troposphere and low stratosphere observed by the Wuhan MST radar with the radiosonde on 22 May 2016, as well as with the ERA-Interim data sets (2016 and 2017) in the long term. Then, we made a comparison of the observed horizontal winds in the mesosphere with the meteor radar and the Horizontal Wind Model 14 (HWM-14) model in the same way. In general, good agreements can be obtained, and this indicates that the Wuhan MST is an effective tool to measure the three-dimensional wind fields of the MST region.

Statistical Study of the Midlatitude Mesospheric Vertical Winds Observed by the Wuhan and Beijing MST Radars in China

AbstractBased on the long‐term observations of the Wuhan and Beijing Mesosphere‐Stratosphere‐Troposphere (MST) radars, the statistic characteristics of the mesospheric vertical winds at midlatitudes are investigated for the first time. The vertical wind data come from the Wuhan MST radar (29.51°N, 114.13°E) during 2012–2017 and from the Beijing MST radar (39.75°N, 116.96°E) during 2012–2014. The subdaily, seasonal, and annual variations of the mesospheric vertical winds at Wuhan and Beijing are presented. No obvious subdaily and seasonal variations are found and the annual variations of the mean vertical winds are downward in most of time. The mean vertical winds at Wuhan become smaller in summer and turn to upward at some heights, while those of Beijing only become smaller in summer. The difference of summer vertical winds over Wuhan and Beijing is closely related to the gravity wave activity. The Wuhan MST radar is located to the east side of the Qinghai‐Tibet plateau and also in the East Asian monsoon region, thus the mesospheric winds over Wuhan may experience more influence of gravity waves compared with those over Beijing. The possible bias sources in the vertical wind measurement of the two MST radars are carefully analyzed and the presented wind velocities are proved to be credible. The measured velocity magnitude is similar to other Very High Frequency radar observations, but much larger than that of the WACCM simulation. The Stokes drift, multicellular circulation structures, the wave influence on the radar echoes are raised as the potential sources for this discrepancy.

Intermittency of Gravity Waves in the Antarctic Troposphere and Lower Stratosphere Revealed by the PANSY Radar Observation

AbstractThe momentum fluxes associated with gravity waves (GWs) significantly vary both in time and space. It is important to qualify the intermittency of GWs because the intermittency largely affects the vertical profile of momentum flux convergences in the middle atmosphere. In this study, 1 year of continuous observation with high time/height resolution and accuracy was provided by the PANSY radar, a Mesosphere‐Stratosphere‐Troposphere (MST) radar at Syowa Station (69.01°S, 39.59°E) in the Antarctic. The PANSY radar is used to study the intermittency of GWs in the troposphere and lower stratosphere. In all seasons, the intermittency is large in the troposphere with Gini coefficients of 0.4–0.6 for absolute momentum fluxes ( ) and 0.4–0.7 for vertical wind variances multiplied by the density ( ). However, the intermittency is small in the lower stratosphere with Gini coefficients of 0.3–0.5 for and 0.2–0.4 for . The seasonal characteristics in the lower stratosphere are different between and : small Gini coefficients are observed in May–July for and in December–February for . Simple model experiments with ideal distributions of GWs as a function of momentum flux magnitude and ground‐based phase velocity are performed. These results indicate that the vertical profiles of the Gini coefficient obtained by the PANSY radar are largely affected by orographic GWs with large amplitudes. The results also suggest that the generation and the partial reflection of GWs play an important role in determining the vertical profile of GW intermittency.

All-atmosphere IS-MST Radar

The IS-MST radar, as the name implies, combines two different methods for studying the atmosphere using a backscatter signal. Turbulent fluctuations of the medium cause scattering in the mesosphere—stratosphere—troposphere (MST). In the upper atmosphere, incoherent scatter (IS) appears in ionospheric plasma. Special-purpose instruments have been built before such that measurements in one of these modes were the most effective. MST radars were utilized for studying wave activity in the lower and middle atmosphere; the IS radar, for ionospheric research. Nowadays, however, for a comprehensive investigation of atmospheric phenomena, it is necessary to have an idea of processes in all atmospheric layers and near-Earth space. The radar, which combines capabilities of IS and MST measurements, will be able to cover layers from the troposphere to the plasmosphere and to study processes of energy transfer from the lower and middle atmosphere to the ionosphere as well as the interaction of the magnetosphere with the upper atmosphere. Apart from atmospheric research, the radar will allow us to track spacecraft and space debris, determining precise coordinate characteristics. The antenna system is also suitable for radio astronomical observations. In the paper, we provide justification for the 154–162 MHz frequency range and discuss technical solutions of the IS-MST radar project and basic operating modes. In addition, we estimate radar diagnostic capabilities for different types of measurements.

Всеатмосферный радар НР-МСТ

The IS-MST radar, as the name implies, combines two different methods for studying the atmosphere using a backscatter signal. Turbulent fluctuations of the medium cause scattering in the mesosphere—stratosphere—troposphere (MST). In the upper atmosphere, incoherent scatter (IS) appears in ionospheric plasma. Special-purpose instruments have been built before such that measurements in one of these modes were the most effective. MST radars were utilized for studying wave activity in the lower and middle atmosphere; the IS radar, for ionospheric research. Nowadays, however, for a comprehensive investigation of atmospheric phenomena, it is necessary to have an idea of processes in all atmospheric layers and near-Earth space. The radar, which combines capabilities of IS and MST measurements, will be able to cover layers from the troposphere to the plasmosphere and to study processes of energy transfer from the lower and middle atmosphere to the ionosphere as well as the interaction of the magnetosphere with the upper atmosphere. Apart from atmospheric research, the radar will allow us to track spacecraft and space debris, determining precise coordinate characteristics. The antenna system is also suitable for radio astronomical observations. In the paper, we provide justification for the 154–162 MHz frequency range and discuss technical solutions of the IS-MST radar project and basic operating modes. In addition, we estimate radar diagnostic capabilities for different types of measurements.

Long‐Term Observations of Stratosphere‐Troposphere Exchange Using MST Radar and Aura MLS Measurements Over a Tropical Station Gadanki

AbstractThis paper presents the climatology of stratospheric intrusion into the troposphere during the Indian Summer Monsoon (ISM) observed using the mesosphere‐stratosphere‐troposphere (MST) radar located at Gadanki (13.5°N, 79.2°E). The most significant and new observation is the presence of enhanced signal‐to‐noise ratio (SNR) of 3 dB and half‐power full spectral width of >0.2 m s−1 in the vicinity of tropopause during the ISM. Downdrafts (updrafts) are dominated in the vicinity of tropopause from April to June (July to March). The result of stratospheric air intrusion is also supported with 10 years of ozone measurements obtained from Aura‐Microwave Limb Sounder (MLS) and 5 years of in situ ozonesonde observations. Detailed analysis shows that the horizontal advection along with turbulence in the vicinity of tropopause caused by the tropical easterly jet and tropopause altitude variability is the prime candidate for stratosphere to troposphere transport of ozone. In contrast, the tropical tropopause temperature plays a significant role in the troposphere to stratosphere transport of water vapor during the ISM. The significance of the present study is to qualitatively constitute the climatology of these exchange processes over Gadanki using Indian MST radar.

Wind Profile Tracking in MST Radar Using Viterbi Data Association

The mesosphere–stratosphere–troposphere (MST) radar is a very high frequency (VHF) pulsed coherent Doppler radar used for ground-based remote sensing. In an MST radar, the backscattered pulses due to fluctuations in atmospheric refractive index are observed at the receiver. Echoes from higher altitudes are typically weaker, resulting in a low signal-to-noise ratio (SNR). They could also be contaminated with clutter and interference, making conventional spectral estimation techniques in the Fourier domain unreliable. In this article, we propose an algorithm to estimate the atmospheric wind profile using a dynamic programming approach employing the Viterbi data association (VDA) algorithm. Progressively for each range bin, the proposed algorithm chooses a set of probable wind speeds as nodes in a trellis. A branch metric incorporating the kinematic parameters inclusive of the differential wind shear is then constructed for state transitions within the trellis, from nodes in one range bin to the subsequent ones. A dynamic programming approach then chooses the optimal wind profile across altitudes. The proposed algorithm is experimented on simulated as well as real MST radar data sets to verify its robustness. Our experiments show that the suggested method has improved performance when compared to previously established techniques.

The Advanced Indian MST Radar (AIR): System Description and Sample Observations

AbstractAn upgraded version of the Indian MST radar, called Advanced Indian Mesosphere‐Stratosphere‐Troposphere (MST) radar (AIR), has recently been commissioned. The prime objective of constructing the AIR is to make it a more useful instrument for conducting new experiments, which enable us to broaden our knowledge on the dynamical and electrodynamical processes including coupling from the boundary layer to the ionosphere. The AIR works at 53 MHz, and the system has been rebuilt, keeping the original square antenna array consisting of 1,024 Yagi antennae. The AIR is a high‐power, fully active phased array system with dedicated 1‐kW solid‐state transmit‐receive units, providing a total peak power of 1,024 kW, and control systems that allow steering the beam with 360° azimuth and 24° zenith agility. Also, the antenna system has been configured with modularity and scalability, which facilitates selection of antenna subarray and aperture for carrying out multireceiver experiments. The antenna radiation pattern tests reveal that the beam width and first side lobe level are close to the designed values of 2.2° and −13.2 dB, respectively. Currently, the system is equipped with 18 receivers to carry out spaced receiver experiments. The transmitters have been designed to transmit very short and long pulses for studying boundary layer to ionosphere. This paper presents the system description of the AIR and sample observations made using the system in Doppler beam swinging mode demonstrating its capabilities for studying neutral atmosphere and ionosphere.

Spectral Analysis of MST Radar Signal using Maximum Likelihood Estimation Algorithm

In this work, we propose Maximum likelihood estimation of low- rank Toeplitz covariance matrix (MELT) with reduced complexity algorithm for computing the power spectral density of mesosphere-stratosphere-troposphere (MST) radar data. MELT is designed based on the method of majorization-minimization and it is an iterative algorithm to update the powers in each successive step. We tested MELT algorithm for complex signal, which contain multiple frequency components in existence of different noise conditions. For simulated complex data, it can be seen that MELT works much better for low Signal to Noise Ratio (SNR) conditions and also effectively detects the frequency components with a fine resolution in the existence with high noise impact. At last, MELT algorithm is applied to the radar data received from MST radar established at National Atmospheric Research laboratory (NARL), Gadhanki. MELT algorithm estimates the accurate Doppler spectra and thus in turn, estimate the wind parameters using Doppler profiles. For the purpose of validation, the obtained radar results through MELT are compared with the Global Positioning System (GPS) radiosonde.

Fast implementation of sparse iterative covariance-based estimation for processing MST radar data

Doppler estimation is an essential problem for the mesosphere–stratosphere–troposphere (MST) radar data for estimation of atmospheric parameters. The Doppler is estimated by computing the power spectral density using either parametric or non-parametric method. A recent class of spectral estimation technique referred as Sparse Iterative Covariance Based Estimation (SPICE) is introduced in literature. SPICE is a sound, user-parameter free, good resolution, iterative and globally convergent method which exhibits the enhanced results than the current spectral estimation methods, at the high computational cost. This letter presents the fast implementation of the SPICE algorithm for the MST radar data and the estimation of various wind parameters at a lesser computational time and is validated with the radiosonde data.