Historical and Projected Surface Temperature over India during the 20th and 21st century.

Surface Temperature (ST) over India has increased by ~0.055 K/decade during 1860-2005 and follows the global warming trend. Here, the natural and external forcings (e.g., natural and anthropogenic) responsible for ST variability are studied from Coupled Model Inter-comparison phase 5 (CMIP5) models during the 20th century and projections during the 21st century along with seasonal variability. Greenhouse Gases (GHG) and Land Use (LU) are the major factors that gave rise to warming during the 20th century. Anthropogenic Aerosols (AA) have slowed down the warming rate. The CMIP5 projection over India shows a sharp increase in ST under Representative Concentration Pathways (RCP) 8.5 where it reaches a maximum of 5 K by the end of the 21st century. Under RCP2.6 emission scenarios, ST increases up to the year 2050 and decreases afterwards. The seasonal variability of ST during the 21st century shows significant increase during summer. Analysis of rare heat and cold events for 2080-2099 relative to a base period of 1986-2006 under RCP8.5 scenarios reveals that both are likely to increase substantially. However, by controlling the regional AA and LU change in India, a reduction in further warming over India region might be achieved

Activity of radon (222Rn) in the lower atmospheric surface layer of a typical rural site in south India

Analysis of one year measurements of in situ radon (222Rn) and its progenies along with surface air temperature, relative humidity and pressure near to the Earth’s surface has been carried out for the first time at the National Atmospheric Research Laboratory (NARL, 13.5∘N and 79.2∘E) located in a rural site in Gadanki, south India. The dataset was analysed to understand the behaviour of radon in relation to the surface air temperature and relative humidity at a rural site. It was observed that over a period of the 24 hours in a day, the activity of radon and its progenies reaches a peak in the morning hours followed by a remarkable decrease in the afternoon hours. Relatively, a higher concentration of radon was observed at NARL during fair weather days, and this can be attributed to the presence of rocky hills and dense vegetation surrounding the site. The high negative correlation between surface air temperature and activity of radon (R = – 0.70, on an annual scale) suggests that dynamical removal of radon due to increased vertical mixing is one of the most important controlling processes of the radon accumulation in the atmospheric surface layer. The annual averaged activity of radon was found to be 12.01±0.66 Bq m−3 and 4.25±0.18 Bq m−3 for its progenies, in the study period

Long-term trends of instability and associated parameters over the Indian region obtained using a radiosonde network

Long-term trends of the parameters related to convection and instability obtained from 27 radiosonde stations across six subdivisions over the Indian region during the period 1980–2016 are presented.  A total of 16 parcel and instability parameters along with moisture content, wind shear, and thunderstorm and rainfall frequencies have been utilized for this purpose. Robust fit regression analysis is employed on the regional average time series to calculate the long-term trends on both a seasonal and a yearly basis. The level of free convection (LFC) and the equilibrium level (EL) height are found to ascend significantly in all Indian subdivisions. Consequently, the coastal regions (particularly the western coast) experience increases in severe thunderstorms (TSS) and severe rainfall (SRF) frequency in the pre-monsoon period, while the inland regions (especially Central India) experience an increase in ordinary thunderstorms (TSO) and weak rainfall (WRF) frequency during the monsoon and post-monsoon periods.  The 16–20-year periodicity is found to dominate the long-term trends significantly compared to other periodicities and the increase in TSS, and convective available potential energy (CAPE) is found to be more severe after the year 1999. The enhancement in moisture transport and associated cooling at 100&thinsp;hPa along with the dispersion of boundary layer pollutants are found to be the main causes for the increase in CAPE, which leads to more convective severity in the coastal regions. However, in inland regions, moisture-laden winds are absent and the presence of strong capping effect of pollutants on instability in the lower troposphere has resulted in more convective inhibition energy (CINE). Hence, TSO and occurrences of WRF have increased particularly in these regions.</p

Assessment of GPS radiosonde descent data

Radiosondes are widely used to obtain basic meteorological parameters such as pressure (<i>P</i>), temperature (<i>T</i>), relative humidity (RH) and horizontal winds during the balloon ascent up to the altitude of balloon burst, usually ~ 32–35 km. Data from the radiosondes released from Gadanki (13.5° N, 79.2° E), a tropical station in India, have been collected during the ascent and during the descent as well without attaching any parachute or its equivalent since the year 2008. In the present study an attempt has been made to characterize the radiosonde descent data with the main objective of exploring its usefulness and reliability for scientific purposes. We compared the data obtained during ascent and descent phases of the same sounding. The mean differences in <i>T</i>, RH and horizontal winds between ascent and descent data are found to be small and are sometimes even within the uncertainty of the measurements and/or expected diurnal variation itself. The very good consistency observed between the ascent and the descent data shows that one more profile of the meteorological parameters can be constructed within 3 h of time of balloon launch practically at no additional cost. Further checks are done by utilizing the 3-hourly radiosonde observations collected during the Tropical Tropopause Dynamics campaigns conducted at Gadanki. In the process of checking the consistency between the radiosonde ascent and descent data, several new findings are arrived at and are reported in this study. In general, it has taken more than half an hour for the balloon to reach the ground from the burst altitude. It is also observed that the fall velocity is close to 10 m s⁻¹ near the surface. Finally, it is suggested to record the observations also when the balloon is descending as this information is useful for scientific purposes

Cloud vertical structure over a tropical station obtained using long-term high-resolution radiosonde measurements

Cloud vertical structure, including top and base altitudes, thickness of cloud layers, and the vertical distribution of multilayer clouds, affects large-scale atmosphere circulation by altering gradients in the total diabatic heating and cooling and latent heat release. In this study, long-term (11 years) observations of high-vertical-resolution radiosondes are used to obtain the cloud vertical structure over a tropical station at Gadanki (13.5°&thinsp;N, 79.2°&thinsp;E), India. The detected cloud layers are verified with independent observations using cloud particle sensor (CPS) sonde launched from the same station. High-level clouds account for 69.05&thinsp;%, 58.49&thinsp;%, 55.5&thinsp;%, and 58.6&thinsp;% of all clouds during the pre-monsoon, monsoon, post-monsoon, and winter seasons, respectively. The average cloud base (cloud top) altitudes for low-level, middle-level, high-level, and deep convective clouds are 1.74&thinsp;km (3.16&thinsp;km), 3.59&thinsp;km (5.55&thinsp;km), 8.79&thinsp;km (10.49&thinsp;km), and 1.22&thinsp;km (11.45&thinsp;km), respectively. Single-layer, two-layer, and three-layer clouds account for 40.80&thinsp;%, 30.71&thinsp;%, and 19.68&thinsp;% of all cloud configurations, respectively. Multilayer clouds occurred more frequently during the monsoon with 34.58&thinsp;%. Maximum cloud top altitude and cloud thickness occurred during the monsoon season for single-layer clouds and the uppermost layer of multiple-layer cloud configurations. In multilayer cloud configurations, diurnal variations in the thickness of upper-layer clouds are larger than those of lower-layer clouds. Heating and cooling in the troposphere and lower stratosphere due to these cloud layers are also investigated and peak cooling (peak warming) is found below (above) the cold-point tropopause (CPT) altitude. The magnitude of cooling (warming) increases from single-layer to four- or more-layer cloud occurrence. Further, the vertical structure of clouds is also studied with respect to the arrival date of the Indian summer monsoon over Gadanki.</p

Studies on atmospheric gravity wave activity in the troposphere and lower stratosphere over a tropical station at Gadanki

MST radars are powerful tools to study the mesosphere, stratosphere and troposphere and have made considerable contributions to the studies of the dynamics of the upper, middle and lower atmosphere. Atmospheric gravity waves play a significant role in controlling middle and upper atmospheric dynamics. To date, frontal systems, convection, wind shear and topography have been thought to be the sources of gravity waves in the troposphere. All these studies pointed out that it is very essential to understand the generation, propagation and climatology of gravity waves. In this regard, several campaigns using Indian MST Radar observations have been carried out to explore the gravity wave activity over Gadanki in the troposphere and the lower stratosphere. The signatures of the gravity waves in the wind fields have been studied in four seasons viz., summer, monsoon, post-monsoon and winter. The large wind fluctuations were more prominent above 10 km during the summer and monsoon seasons. The wave periods are ranging from 10 min-175 min. The power spectral densities of gravity waves are found to be maximum in the stratospheric region. The vertical wavelength and the propagation direction of gravity waves were determined using hodograph analysis. The results show both down ward and upward propagating waves with a maximum vertical wave length of 3.3 km. The gravity wave associated momentum fluxes show that long period gravity waves carry more momentum flux than the short period waves and this is presented

Macro-physical, optical and radiative properties of tropical cirrus clouds and its temperature dependence at Gadanki (13.5° N, 79.2° E) observed by ground based lidar

The macro-physical and optical properties of cirrus clouds and its temperature dependencies have been investigated at the National Atmospheric Research Laboratory (NARL; 13.5° N, 79.2° E), Gadanki, Andhra Pradesh, India; an inland tropical station during the period of observation January to December 2009 using a ground based pulsed monostatic lidar system data and radiosonde measurements. Based on the analysis of measurements the cirrus macrophysical properties such as occurrence height, mid cloud temperature, cloud geometrical thickness, and optical properties such as extinction coefficient, optical depth, depolarization ratio and lidar ratio have been determined. The variation of cirrus macrophysical and optical properties with mid cloud temperature have also been studied. The cirrus clouds mean height has been generally observed in the range of 9-17 km with a peak occurrence at 13-14 km. The cirrus mid cloud temperatures were in the range from -81 °C to -46 °C. The cirrus geometrical thickness ranges from 0.9-4.5 km and 56% of cirrus occurrences have thickness 1.0 -2.7 km. The monthly cirrus optical depth ranges from 0.01-0.47, but most (&gt;80%) of the cirrus have values less than 0.1. The monthly mean cirrus extinction ranges from 2.8E-06 to 8E-05 and depolarization ratio and lidar ratio varies from 0.13 to 0.77 and 2 to 52 respectively. The temperature and thickness dependencies on cirrus optical properties have also been studied. A maximum cirrus geometrical thickness of 4.5 km is found at temperatures around – 46 °C with an indication that optical depth increases with increasing thickness and mid cloud temperature. The cloud radiative properties such as outgoing long-wave radiation (OLR) flux and cirrus IR forcing are studied. OLR flux during the cirrus occurrence days ranged from 348-456 W/m2 with a low value in the monsoon period. The cirrus IR forcing varied from 3.13 – 110.54 W/m2 and shows a peak at monsoon period

Patchy layered structure of tropical troposphere as seen by Indian MST radar

The MST radar observations at Gadanki (13.47° N, 79.18° E) show, almost every day throughout the year, stratified layers of intense reflectivity near the tropopause level (17 km) and also at a couple of levels between 4 km and 10 km. Highest individual reflectivity values occur near 17 km, but they occur for a short while. The region between 11 km and 15 km shows the lowest values of reflectivity alongwith vertical downward motion almost on all days of the year. High values of reflectivity are attributed to the existence of visible or sub-visible clouds; the layered structure of clouds is attributed to inertio-gravity waves with vertical wavelength of 2-3 km. It is suggested that each high reflectivity layer consists mainly of thin sheets and patches of visible and sub-visible cloud material. Hydrometeors inside the cloud material go up and down due to gravity, precipitation-loading, Brunt-Vaisala oscillations, and Kelvin-Helmholtz waves. In these small-scale motions, thin air sheets and patches get formed with sharp temperature and humidity discontinuities through contact cooling, melting, evaporation, condensation and freezing. Also, melting and freezing at low temperatures generate electrical charges in these thin sheets and patches. These thin sheets and patches have vertical dimensions ranging from a few centimetres to several metres and horizontal dimensions of the order of 1km. These thin sheets and patches have corresponding vertical and horizontal discontinuities and sharp gradients in refractive index for the MST radar beam. These show up as regions of high values of reflectivity