The present study analyses the response of the Brewer-Dobson Circulation (BDC) in the stratosphere to a quadrupled CO2 experiment in the CMIP6 using the MRI ESM2.0 model. The signatures of the greenhouse gas increase are analysed in the BDC metrics evaluated from the temperature and winds from the ERA5 reanalysis for comparison of recent-period changes. As the changes in BDC will impact the ozone and water vapour measurements in the stratosphere, the variations in these trace gases are evaluated from Aura Microwave Limb Sounder. The analysis shows an enhanced circulation in the quadrupled CO2 experiment, with the lower stratospheric summer hemispheric circulation gaining strength. The ozone and water vapour in the stratosphere show enhancement throughout the depth of the stratosphere, but with a negative ozone anomaly in the lower stratosphere. The pattern of the experiment output is broadly consistent with MLS measurements. The BDC metrics evaluated from ERA5 dynamical variables, combined with independent measurements from the Aura Microwave Limb Sounder, suggest a strengthening of the circulation, accompanied by discernible changes in stratospheric ozone, and water vapour.

Abstract The present study examines the roles of advection and air compression in enhancing the stratospheric ozone layer over the North Bay of Bengal during winter. The most significant and novel observation reported is an increase in the stratospheric ozone layer between 21 and 23 km, with ozone partial pressure approximately 50 nbar higher than the typical profile in the eastern Indian subtropical region. The thickness of the observed ozone layer ranges from 2.1 to 2.4 km. Potential vorticity derived from reanalysis and vertical air motion from the Stratosphere‐Troposphere radar observations also supports the enhanced stratospheric ozone layer. Space‐borne ozone measurements also reveal the presence of a sporadic ozone layer structure over the North Bay of Bengal. These observations provide quantitative experimental evidence of the redistribution of stratospheric ozone over the Indian subtropical region during winter.

The response of the stratospheric Brewer–Dobson Circulation (BDC) to Quasi–Biennial Oscillation (QBO) is evaluated using a composite of QBO cycles from 1979 to 2021. In an attempt to delineate the response of the meridional circulation, the BDC metrics derived from 43 years of climatological reanalysis dataset from ERA5 are used. An enhancement in the wave breaking in the stratosphere is observed in the westward phase of QBO. This is reflected in an increased residual meridional transport. The modulation of BDC is more evident in the Northern Hemisphere, where the zonal wind structure is more responsive to QBO. The ozone mixing ratio observed from the Aura Microwave Limb Sounder shows well-marked QBO signatures in the lower and middle stratospheres. During the westward (eastward) QBO phase at 50 hPa, negative anomalies of 0.2 ppmv (positive, 0.2 ppmv) are observed over the tropical lower stratosphere. The water vapor is influenced by QBO at the stratospheric entry, where the cold point tropopause temperature is much lower in the westward phase of QBO, leading to a dry anomaly of 0.1 ppmv. The concentration changes lead the instantaneous radiative forcing to vary between 0.11 to 0.14 Wm ^-2 during QBO phases.

The stratospheric water vapor injected on the eruption of the submarine volcano, Hunga-Tonga Hunga Ha’apai, caused cooling in the stratosphere and warming at the Earth’s surface. The Aura Microwave Limb Sounder observed water vapor mixing ratios as high as 12 ppmv in the stratosphere. The surface temperature observed by the India Meteorological Department from 350 ground stations shows a warming of ∼4 K. This is accompanied by the stratospheric cooling observed from COSMIC-2 radio occultation measurements. The ERA5 reanalysis data over the Indian region also shows a similar cooling during March 2022. The radiative cooling due to the Tonga-injected water vapor is confirmed by the model simulations using the radiative-convective model. The concurrent warming points to the influence of stratospheric water vapor in the surface temperature anomaly over the Indian region.

First observations on the characteristics of vertical velocity during the Asian Summer Monsoon (ASM) months, over the central Himalayan region using 206.5 MHz Stratosphere-Troposphere radar are presented. Clear air zenith observation data have been extracted and analyzed to determine the distribution of vertical velocity occurrence and the mean vertical velocity profiles up to 16 km from June to October. Results show that the mean updraft and downdraft characteristic velocity similar to 4 km did not generally exceed 5 cm s-1 for all the months. An exception to this feature is observed as a layer of persistent downdraft between 10 and 11 km with a maximum mean vertical velocity of similar to-7 cm s-1 in August, which is new observation. Consistent downdrafts in the lower troposphere and consistent updrafts in the upper troposphere above 12 km show that direct transport of airmass from lower to upper level and vice versa is not climatologically supported. In turn, such profile shows similarity to the two-step process of upliftment of air mass in the tropical region. Notably this height corresponds to the lower level of ASM Anticyclone and gives insight in to the entrapment and slow upliftment of airmass toward stratosphere. Further analysis of inter-period variability of vertical velocity for forenoon, afternoon, and evening periods for all the months show notable variations in the mid-tropospheric region with barely any change in the upper troposphere above 12 km, indicating that the slow upward transport does not directly depend on the inter-period variability for any of the months.

The present study deals with the effect of Hunga Tonga-Hunga Ha'apai volcanic eruption on altering the structure of Brewer -Dobson circulation (BDC) that occurred on 15 January 2022. The strength of the stratospheric circulation declined during the Southern Hemi- spheric winter following the volcanic eruption. The eruption had substantial impacts on the stratospheric thermal structure and compo- sition. The Eliassen-Palm flux divergence implies the wave breaking was nearly non-existent. Thus, the wave driven circulation's strength was reduced following the injection of water vapor. The reduction in meridional transport was also reflected in the distribution of ozone in the Southern Hemisphere obtained from Aura Microwave Limb Sounder. An unprecedented deviation of ozone mixing ratio, with magnitude 0.55 ppmv, was observed following the eruption over the tropical stratosphere. (c) 2024 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

The changes in the intensity of Brewer-Dobson circulation (BDC) in the record-breaking Southern Hemisphere sudden stratospheric warming (SH SSW) event in 2019 are investigated in the present study. Wave driving was observed to be at its highest in 2019 SH SSW, despite the event being classified as a minor warming event. The Eliassen-Palm flux divergence, indicative of wave driving, was observed to be increasing before the SSW, and subsiding afterwards. The stratospheric circulation followed the wave driving and intensified along the warming episode. The resulting stratospheric distribution from Aura Microwave Limb Sounder showed a negative ozone anomaly (-20%) in the tropical lower stratosphere and a downward propagating positive anomaly in the Southern Hemisphere polar stratosphere around the central dates. The water vapor mixing ratio showed an increase of more than 25% in the polar lower stratosphere and 10% in the tropical upper stratosphere. A cooling of about 5 K was observed in the tropical middle stratosphere. The results indicate that SH SSW can change the intensity of the stratospheric circulation which in turn affects the ozone and water vapor transport from the tropics to the pole. (c) 2023 COSPAR. Published by Elsevier B.V. All rights reserved.

An empirical model of temperature is developed using long-term observations of radiosonde (52 years), M-100 Rocket (17 years), and Sounding of the Atmosphere by Broadband Emission Radiometry (SABER) (22 years) data. The dominant oscillations such as Annual Oscillation (AO), Semi-Annual Oscillation (SAO), Terr-Annual oscillation (TAO), and Quasi-Biennial Oscillation (QBO) variability has been incorporated into the temperature to obtain the empirical atmosphere. The monthly mean of temperature obtained from radiosonde from 0 to 25 km, M-100 rocket from 26 to 80 km and SABER from 26 to 109 km has been subjected to the Fast Fourier Transform technique to retrieve the amplitudes and phases of AO, SAO, TAO, and QBO. The amplitudes and phases obtained are put in an empirical formula along with the temperature obtained from the observations to retrieve the empirical temperature. The empirical model is developed for two epochs (1971-1990, and 2002-2023). The amplitude is similar in both epochs for the TAO, and it is high in the first compared to the second epoch for SAO, AO, and QBO. The peak in the amplitude (3-4 K) is obtained between 80 and 90 km for TAO, and between 70 and 80 km (2-3 K) for SAO. The amplitude is less than 1 K for AO in both the epochs. The peaks in the QBO are observed between 20 and 30 km (2-3 K), another between 60 and 70 km (3-4 K) in the first epoch and above 80 km (2-3 K). Downward phase propagation is dominant for all the oscillations observed below 50 km, and upward propagation above. The empirical temperature obtained compares well with the observations below 20 km (RMSE <1 K) and shows differences above it (RMSE similar to 4-6 K). This is due to the fact, that the amplitude of the oscillation is more in the stratosphere and mesosphere which results in perturbation of the background temperature. (c) 2024 COSPAR. Published by Elsevier B.V. All rights reserved.

This paper presents the first ever observations on aspect-sensitive characteristics of 205 MHz stratosphere-troposphere (ST) radar located at a tropical station Cochin (10.04 degrees N, 76.3 degrees E) using volume scanning. The most significant and new observation is that the signal-to-noise ratio in zenith and off-zenith beams are nearly equal in some height region, indicating the presence of isotropic turbulence. Signal strength decreases by 0.75 dB per degree from 0 to 10 degree off-zenith, 0.9 dB per degree from 10 to 20 degree off-zenith and 0.3 dB per degree beyond 20 degree off-zenith. Different causative mechanisms are discussed on the basis of various estimated parameters associated with aspect sensitivity. Maximum aspect sensitivity is observed between 12 and 17 km, indicating the presence of dynamic instability arising due to strong wind shear and atmospheric stability. When both the square of wind shear and stability parameters are above 0.25 x 10-3 s-2, the scatterers become mostly isotropic. The study also shows a power difference in the symmetric beams as well as azimuth angle dependency. Analysis suggests that this asymmetry is due to the tilting of layers by the action of atmospheric gravity waves generated through Kelvin-Helmholtz instability. The present configuration of radar can provide a better understanding of three-dimensional structures of turbulence and instabilities. Radar backscatter from the atmosphere depends directly on the turbulent scale sizes present and the probing frequency. When the backscatter echo strength decays with the radar viewing zenith angle, the signals are said to be aspect sensitive that is, dependent on the viewing angle. There can be few circumstances under which such characteristics are observed, all primarily being anisotropic scattering processes which are caused due to various processes in the atmosphere. Such aspect sensitivity must be quantified for realizing the accurate operation of a radar which would otherwise result in underestimation of winds and other parameters obtained from the radar. Here the aspect sensitivity characteristics of the 205 MHz stratosphere-troposphere (ST) radar installed at Cochin (10.04 degrees N, 76.33 degrees E) are studied using a detailed experiment using various probing techniques during Indian Summer Monsoon season and the characteristics of the atmosphere during that period are probed to explain the aspect sensitivity. First observations of aspect-sensitivity characteristics at 205 MHz stratosphere-troposphere radar Mechanisms for the formation of isotropic and anisotropic turbulence Modulation of aspect sensitivity by wind shear and atmospheric stability

This paper describes the first assessment of ISRO's indigenously developed S-band Polarimetric Doppler Weather Radar (DWR) at Sriharikota High Altitude Range (SHAR), Sriharikota (13.66 degrees N, 80.23 degrees E). The assessment is done during the passage of a tropical cyclone 'Phethai' and four different cases of Mesoscale convective systems. A comparison of reflectivity measured from SHAR-DWR with India Meteorological Department (IMD) DWR located at Chennai (13.07 degrees N, 80.28 degrees E) and Ku-band space-borne radar of the Global Precipitation Mission (GPM) is done using the common volume matching method. A good comparison is observed between SHAR-DWR with IMD-DWR and GPM-Ku radar in both space and height. The vertical structure of the cyclone is provided using Contour Frequency by Altitude Diagrams (CFAD) which show the vertical extent up to an altitude of 16 km with a reflectivity between 25 and 30 dBZ. Maximum occurrence of 30 dBZ occurs below 6 km. Bright band signatures show similar to 25 dBZ between 4 and 5 km depicting the stratiform precipitation of the cyclone. Further rain rate is estimated using both reflectivity and the polarimetric product which compared well with rain estimated from IMD-DWR and rainfall observed from rain gauges. Rain rate is observed from 5 to 35 mm hr(-1). Hydrometer classification during the passage of tropical cyclone 'Phethai' shows the presence of rain below 4 km and graupels, ice crystals, and large droplets above.

The Asian Summer Monsoon Anticyclone (ASMA) is a gateway for atmospheric pollutants transported to the upper troposphere and lower stratosphere (UTLS). Thus, it is necessary to understand the relative roles of vertical transport due to convection and horizontal transport due to advection in the formation and sustenance of the ASMA. Outgoing longwave radiation reveals that the ASMA region shows characteristic features associated with strong convective activity in its eastern (70°–120° E) part while subsidence dominates in the western (20°–70° E) part. Over the convective region, the convergence of latent heat flux extends from the Indian mainland (65°–110° E) to the west Pacific Warm Pool (WP) (110°–160° E). On average the ASMA region is characterized by a main convective outflow level at 9 km. This level varies considerably with longitude being higher ( 10.5 km) over the convective region and lower ( 7 km) over the subsidence region. Furthermore, the mean convective outflow level is higher over the WP (11.5 km) region when compared to the Indian mainland (10 km) region. From the thermodynamic energy equation, we have calculated the convective and advective terms and found anomalously cold advection over the subsidence region and warm advection over the convective region. The warm advection over the convective region is split into two parts with the stronger one located over the Indian region and the weaker one over the WP region. Similarly, stronger convection occurs over the Indian mainland (convective term 4 K/day) compared to the WP ( 1 K/day). The cold advection over the subsidence region is mainly centered near 30° E longitude. The convection over the Indian region and the cold advection over the subsidence region as well as warm advection and convection over the WP region are associated. We find that the advective terms change in magnitude and shift together with the convective terms in response to signals of the El Nino Southern Oscillation and the Indian Ocean Dipole.

Abstract We quantify the changes in the intensity of Brewer‐Dobson Circulation (BDC) during sudden stratospheric warming (SSW) and its impact on the tropical stratospheric thermal structure and ozone distribution by composite analysis using observations and a chemical‐transport model. An increase in the planetary wave activity and enhancement in BDC intensity before the central date of SSW is noticed. A positive ozone anomaly is observed in the tropical upper stratosphere. The tropical lower stratosphere shows a cooling (1–2 K) and negative ozone anomaly (∼0.1 ppmv) after ∼10 days from the central date. The polar stratosphere experiences a positive ozone anomaly, whereas the upper stratosphere shows ozone depletion due to the downwelling of NOx‐rich mesospheric air. The cold‐point tropopause temperature shows a cooling of ∼0.5 K for major warming which in turn dries the lower stratosphere.

Abstract An integrated campaign “Suryagrahan‐2019” with multi‐institutional support was conducted by launching a series of radiosondes/ozonesondes over 6‐different locations in India along with the operation of ST/MST radars and launching of RH‐200 rockets during the annular solar eclipse of 26 December 2019. We present the eclipse‐induced changes in the thermal structure, dynamics and trace gases in the lower and middle atmosphere. One of the novel findings is the formation of three step‐like isothermal structures in the lower stratosphere with a layer height of 1.4, 2.5, and 4 km, which is attributed to the adiabatic compression and expansion of the air parcel. These structures have both warming and cooling effect of the order of ±6 K. A significant increase of ozone by 20% in post‐eclipse scenario between 29 and 32 km is observed over Cochin. Strong downdrafts of ∼−0.25 m s−1 are observed between 12 and 16 km during the eclipse event, which is attributed to the atmospheric compression due to the sudden cooling during the eclipse event. Due to the changes in thermal structure, the atmospheric circulation changes are observed in the meridional wind. During the maximum obscuration, there is a sudden decrease in near‐surface and boundary layer ozone by 12–15 ppbv. The present study reiterates that the eclipse‐induced perturbations depend on the local time of the eclipse event and place of observations. It is envisaged that the results discussed in the study will improve our understanding of the eclipse induced perturbations in the Earth's atmosphere.