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This article examines the role of the meteorological variable in the spread of the ongoing pandemic coronavirus disease 2019 (COVID-19) across India. COVID-19 has created an unprecedented situation for public health and brought the world to a standstill. COVID-19 had caused more than 1,523,242 deaths out of 66,183,029 confirmed cases worldwide till the first week of December 2020. We have examined the surface temperature, relative humidity, and rainfall over five cities: Delhi, Mumbai, Kolkata, Bengaluru, and Chennai, which were severely affected by COVID-19. It is found that the prevailing southwest (SW) monsoon during the pandemic has acted as a natural sanitizer in limiting the spread of the virus. The mean rainfall is ~ 20-40 mm over the selected cities, resulting in an average decrease in COVID cases by ~ 18-26% for the next 3 days after the rainfall. The day-to-day variations of the meteorological parameters and COVID-19 cases clearly demonstrate that both surface temperature and relative humidity play a vital role in the indirect transport of the virus. Our analysis reveals that most COVID-19 cases fall within the surface temperature range from 24 to 30 °C and relative humidity range from 50% to 80%. At a given temperature, COVID-19 cases show a large dependency on the relative humidity; therefore, the coastal environments were more prone to infections. Wavelet transforms coherence analysis of the daily COVID-19 cases with temperature and relative humidity reveals a significant coherence within 8 days.

The extreme variability of the cold point tropopause temperature (TCPT) and height (HCPT) are examined over a tropical station, Gadanki (13.45N, 79.2E) using high-resolution radiosonde data during ...

In this study, we have characterized the tropical tropopause parameters such as the cold point tropopause (CPT) height (CPT-H) and temperature (CPT-T), convective tropopause (COT) height (COT-H) and temperature (COT-T), and the tropical tropopause layer (TTL) using radiosonde observations during 2014–2019 over Chennai (13.0oN, 80.06oE) located in the northeast (NE) monsoon region. The water vapor and ozone data from the microwave limb sounder (MLS) simultaneous to the radiosonde observations are also utilized to understand their roles on the CPT variations for different convective conditions obtained from Infrared brightness temperature (IRBT) data. CPT over Chennai becomes higher (17.6 ± 0.3 km) and colder (189.7 ± 0.9 K) during the winter season and lower (16.6 ± 0.2 km) and warmer (192.1 ± 1.0 K) during the summer monsoon season, however, not in the same month. The water vapor (CPT-W) and ozone (CPT-O) mixing ratios at CPT are found to be lower (~ 70 ± 1.4 ppmv and 3.1 ± 0.4 ppmv) during the winter season and higher (153 ± 4.2 ppbv and 4.8 ± 0.6 ppmv) during summer monsoon season. COT, however, becomes lower (12.4 ± 0.3 km) and higher (13.3 ± 0.3 km) during premonsoon and summer monsoon seasons, respectively. The TTL thickness is lesser (3.5 ± 0.6 km) and greater (4.8 ± 0.8 km) during winter and summer monsoon seasons. Over Chennai, the seasonal variation of the upper troposphere and lower stratospheric temperature, water vapor, and ozone anomalies are found to be in phase. We have categorized tropical convections as non-penetrative and penetrative. It is observed that the TTL temperature warms with the increasing strength of the non-penetrative convections and cools for the penetrative convection.

Continuous monitoring of the planetary boundary layer (PBL) height was carried out using simultaneous observations of the micro-pulse lidar (MPL) at Kattankulathur (12.83°N, 80.04°E) and radiosonde and surface meteorological observations at Meenambakkam (13.0°N, 80.18°E) during different seasons in the year 2016 over Chennai, in the Indian east coast region. These observations provide excellent data to evaluate the performance of the five different PBL parameterization schemes from the Weather Research and Forecasting (WRF) model simulation of PBL characteristics over the coastal environment. The simulation experiments were run using Asymmetrical Convective Model version 2 (ACM2), Yonsei University (YSU), Mellor-Yamada-Janjic (MYJ), Mellor-Yamada Nakanishi and Nino level 2.5 (MYNN2), and Bougeault–Lacarrere (BouLac) schemes. The first two schemes are the first-order closure schemes, while the last three schemes are the turbulent kinetic energy (TKE) closure schemes. We have conducted the experiments for dry and wet surface conditions on clear sky days during different seasons. Under the dry surface conditions, the comparison of the simulated PBL height with observation reveals that all the schemes perform well during the daytime. However, during night-time, all the schemes except MYNN2 underestimate the observation. MYNN2 simulates the similar PBL diurnal pattern as detected by MPL. The potential temperature and relative humidity (RH) profiles from radiosonde observations at 00Z and 12Z and their surface observations at every 1-h interval from automatic weather station are also compared with simulated results. In the case of surface parameters, the WRF model underestimates the surface temperature by ~ 2 K and surface relative humidity by ~ 10–20% for the dry surface condition. However, under the wet surface condition, simulated PBL height and surface temperature (RH) overestimate (underestimate) the observation first 8 h after the rainfall.

Knowledge of the spatiotemporal coverage of cirrus clouds is vital in quantifying the radiation budget of the Earth–atmosphere system. In this paper, we present the diurnal and vertical distributions of the occurrence of cirrus clouds during different seasons as well as the interannual variation in the occurrence of cirrus over Kattankulathur (12.82∘ N, 80.04∘ E) on the west coast of the Bay of Bengal. Long-term (2016–2018) continuous micropulse lidar (MPL) observations demonstrate laminar and descending cirrus clouds that occur either as single or multiple layers. The single-layer cirrus occurrence shows a diurnal pattern with frequent occurrence in the late evening (∼ 30 %–40 %), whereas multilayer cirrus clouds occur in the early morning (∼ 10 %–20 %). For the diurnal pattern in single-layer cirrus cloud occurrences, convective processes dominate during the pre-monsoon, southwest (SW) monsoon, and northeast (NE) monsoon seasons, while the freeze-drying process is favorable during the winter season. However, both convective and freeze-drying processes are dominant in the diurnal pattern of the multilayer cirrus occurrences. The occurrence reaches a maximum (∼ 40 %) during the SW and NE monsoon seasons, and it shows a minimum (∼ 25 %) during the winter season. The vertical distributions indicate that the maximum occurrence is confined within the tropical tropopause layer (TTL) during all seasons. Cirrus cloud rarely occurs above the tropopause; however, it frequently occurs below the TTL during all seasons. The vertical extent of the occurrence has a broader altitudinal coverage (∼ 8–17 km) during December–March and June–September, while the altitudinal coverage is narrower during April–May (∼ 10–17 km) and October–November (∼ 9–15 km). Cirrus cloud occurrence also exhibits interannual variations, with higher occurrence during 2016 compared with 2017 and 2018, in association with the El Niño–Southern Oscillation (ENSO).

The relationship ( $$\varvec{Z} = \varvec{AR}^{\varvec{b}}$$ ) between radar reflectivity factor, $$\varvec{ Z }$$ and rainfall rate, $$\varvec{R }$$ is studied using the micro rain radar (MRR) observation located over Darjeeling (27.05° N, 88.26° E, 2194 m above the msl) in the foothills of the eastern Himalayan Mountains during Indian summer monsoon and post monsoon seasons (June–October) 2013. Observations from MRR are classified mainly into two types, stratiform and convective, based on the bright band and non-bright band signatures in the radar reflectivity, respectively. We have observed 12 and 7 cases for the stratiform convective rain events, respectively. In the present study MRR is operated mostly during low intensity rainfall rate (0.02–20 mm/h). During southwest monsoon season $$\varvec{Z} {-} \varvec{R }$$ relation for the stratiform and convective rainfall types are found to be $$\varvec{Z} = 272\varvec{R}^{1.78}$$ and $$\varvec{Z} = 192\varvec{R}^{1.54}$$ respectively. $$\varvec{Z} {-} \varvec{R }$$ relation for both stratiform and convective rain shows high temporal variation during different months of monsoon and post monsoon seasons. The coefficient $$\varvec{A}$$ varies between 225 and 289 for stratiform rain and between 153 and 235 for convective rain. The exponent $$\varvec{b}$$ varies between 1.4 and 2.1 for stratiform rain while between 1.2 and 1.8 for convective rain. Interestingly, we observed a distinct relation with smaller values of $$\varvec{A}$$ and $$\varvec{b}$$ for convective rain than stratiform rain over Darjeeling. The height dependence of $$\varvec{A}$$ and $$\varvec{b}$$ are also studied which is found to be very small up to ~ 1.5 km above the surface for both types of the precipitating systems.

Characteristics of the sea breeze and thermal internal boundary layer (TIBL) during different seasons are studied using mini micropulse lidar (MPL) at Kattankulathur (12.83° N, 80.04° E, 45 m) and radiosonde and surface meteorological observations at Meenambakkam (13.0° N, 80.06° E, 16 m) during the period January 2016–June 2018 over Chennai, in the Indian east coast region. Study of the sea breeze is important because it is one of the main factors responsible for most of the convective rainfall during summer monsoon season over Chennai. The sea breeze onset occurs from morning ~ 07:00 IST to late afternoon during winter and pre-monsoon seasons whereas it occurs from mid-morning ~ 09:00 IST to late evening ~ 19:00 IST during the summer monsoon and post-monsoon seasons. The cessation of the sea breeze lies between the late evening ~ 18:00 IST and early morning ~ 04:00 IST on the next day. Sea breeze prevails for the longest (shortest) duration during pre-monsoon (summer monsoon) season. The temperature, moisture, refractivity, and aerosol profiles show double mixed layer characteristics indicating TIBL as the first layer and convective boundary layer (CBL) or residual layer (RL) as the second layer. TIBL occurs throughout the year with maximum occurrence during pre-monsoon season. It varies from 0.2 to 0.8 km (0.4–1.0 km) with peak at 0.4 km (0.6 km) over Meenambakkam (Kattankulathur). TIBL height is found to be at altitude ~ 0.54 ± 0.16 km and 0.62 ± 0.13 km at Meenambakkam and Kattankulathur, respectively. TIBL shows a weak seasonal variation with maximum height during winter and minimum height during summer in contrast to the seasonal variation of the CBL.

Knowledge of the spatiotemporal coverage of the cirrus clouds is vital in quantifying the radiation budget of the earth-atmosphere system. In this paper, we present the diurnal and vertical distributions of the occurrence of the cirrus clouds during different seasons as well as its interannual variation over Kattankulathur (12.82° N, 80.04° E), east coast of the Bay of Bengal. The long-term (2016–2018) continuous observations of micropulse lidar (MPL) demonstrate the laminar and descending cirrus clouds that occur either as single or multiple layers. The single-layer cirrus occurrence shows a diurnal pattern with frequent occurrence in the late evening (~30–40 %) while multiple-layer cirrus clouds occurrence and early morning (~10–20 %), respectively. For the diurnal pattern in single layer cirrus cloud occurrences, convective processes dominate during the pre-monsoon, southwest (SW), and northeast (NE) monsoon seasons, while the freeze-drying process is favourable during the winter season. However, both convective and freeze-drying processes are dominant in the diurnal pattern of the multiple-layer cirrus occurrences. The occurrence is maximum (~40 %) during the SW and NE monsoon seasons and minimum (~25 %) during the winter. The vertical distributions indicate that the maximum occurrence is confined within the tropical tropopause layer (TTL) during all the seasons. The cirrus cloud rarely occurs above the tropopause; however, it frequently occurs below the TTL during all the seasons. The vertical extent of the occurrence has broader altitude coverage (~8–17 km) during December–March and June–September while narrower during April–May (~10–17 km) and October–November (~9–15 km). The cirrus clouds occurrence also exhibits interannual variations with higher occurrence during 2016 compared to 2017 and 2018 in association with El Nino Southern Oscillation (ENSO).

Micro rain radar (MRR-2) provides the measurement of the drop size distribution DSD with altitude and rain rates. In this paper, we show a new form of gamma drop size distribution (DSD) model. MRR-2 is based on the principle of Radar spectrum measurement of continuous-wave of frequency modulation. DSD measurements for the rain rates ~ 0–25 mm/h and the height from 150 to 2000 m during the south-west monsoon season for the period 2009 and 2010 are used in this study. From the variance of DSD ( $$\sigma^{2}$$ ) and mass-weighted mean drop diameter as well as after the mathematical calculation, two parameters ( $$\varLambda$$ and µ) are obtained for the use of lower-order moments. Both the moments are utilized for the best suitable of gamma DSD. Measured DSD for the different rain rates and different altitudes below the melting layer height (~ 2–3 km) compared among the exponential, lognormal and gamma DSD model over Darjeeling in the Eastern Himalaya. The correlation between best fit measured DSD and gamma distribution indicate that they correlate well for both lower and higher order moments for the heights 150 m and 1050 m. Whereas they correlated only for higher order moments for the 450 m, 1500 m and 1950 m. Thus, it is found that the observed pattern of DSD agrees well to the gamma DSD model.

This paper examines the role of the meteorological variable on the spread of the ongoing pandemic coronavirus disease 2019 (COVID-19) across India. COVID-19 has created an unprecedented situation for public health and brought the world to a standstill. The COVID-19 has caused more than 1,523,242 deaths out of 66,183,029 confirmed cases and around the world till the first week of December 2020. We have examined the surface temperature, relative humidity, and rainfall over five cities namely Delhi, Mumbai, Kolkata, Bengaluru, and Chennai severely affected by COVID-19. It is found that the prevailing southwest (SW) monsoon during the pandemic has acted as a natural sanitizer in limiting the spread of the virus. The day-to-day variation of the meteorological parameters and COVID-19 cases clearly demonstrate both surface temperature and relative humidity play a vital role in the indirect transport of the virus. Our analysis reveals that the majority of the COVID-19 cases fall within the surface temperature ranging from 24oC to 30oC and relative humidity ranging from 50–80%. At a given temperature, COVID-19 cases show a large dependency on the relative humidity which attributes those coastal environments were more prone to infections. Wavelet transforms coherence analysis of the daily COVID-19 cases with temperature and relative humidity reveal a significant coherence within 8 days.

Bone metabolism constitutes the intricate processes of matrix deposition, mineralization, and resorption. Any imbalance in these processes leads to traumatic bone injuries and serious disease conditions. Therefore, bone remodeling plays a crucial role during the regeneration process maintaining the balance between osteoblastogenesis and osteoclastogenesis. Currently, numerous phytobiologics are emerging as the new therapeutics for the treatment of bone-related complications overcoming the synthetic drug-based side effects. They can either target osteoblasts, osteoclasts, or both through different mechanistic pathways for maintaining the bone remodeling process. Although phytobiologics have been widely used since tradition for the treatment of bone fractures recently, the research is accentuated toward the development of osteogenic phytobioactives, constituent-based drug designing models, and efficacious delivery of the phytobioactives. To achieve this, different plant extracts and successful isolation of their phytoconstituents are critical for osteogenic research. Hence, this review emphasizes the phytobioactives based research specifically enlisting the plants and their constituents used so far as bone therapeutics, their respective isolation procedures, and nanotechnological interventions in bone research. Also, the review enlists the vast array of folklore plants and the newly emerging nano-delivery systems in treating bone injuries as the future scope of research in the phytomedicinal orthopedic applications.

This paper presents the first quantitative relationship between the cold point tropopause (CPT) and tropical easterly jet (TEJ) using radiosonde observations over Gadanki (13.45oN, 79.2oE) during t...

Spatial and temporal variability in the convective boundary layer (CBL) height for the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) study period are examined using the data collected from high-resolution radiosondes during May–September 2009 over the Indian monsoon region. In total, 57 radiosonde launchings were carried out at ∼ 11:00–17:00 IST over six different stations covering a large geographical region, ranging from latitude ∼ 13 to 32° N and longitude 73 to 92° E. Of the total 57 launchings, 17 were made during cloudy conditions during which relative humidity (RH) was found to be greater than 83 % for an ∼ 1.0 km layer at various altitudes below 6 km. Within the layer the difference between saturated equivalent potential temperature and equivalent potential temperature is small, and it satisfies the condition that RH > 83 % for about 1 km is considered as the cloudy layer. There are eight cases when the cloud-topped boundary layer (CTBL) and 19 cases when fair-weather boundary layer (FWBL) is observed. The CBL heights are obtained using thermodynamic profiles, which vary from ∼ 0.4 to 2.5 km a. g. l. The formation of the cloud layers above the boundary layer generally lowers the CBL height and is responsible for its day-to-day variability. The development of the cloud beneath the boundary layer generally elevates the CBL, which is also responsible for the large day-to-day variability in the CBL. The FWBL identified using relative invariance of the thermodynamic profiles varies from ∼ 2.0 to 5.5 km, which is clearly marked by a local minimum in the refractivity gradient. During cloudy days, the CBL is found to be shallow and the surface temperature lower when compared to clear-sky days. The CBL and the lifting condensation level (LCL) heights are randomly related and are found to be at a lower height during cloudy days when compared to clear-sky days. Finally, the typical comparison between the CBL height obtained using thermodynamic profiles and backscattering profiles using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) is examined.

Seasonal characteristics of the aerosols over Kattankulathur (12.83° N, 80.04° E) is studied using Micro Pulse Lidar observations during 2016–2018 and Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observation, Moderate Resolution Imaging Spectroradiometer and Ozone Monitoring Instrument datasets during 2006–2018. The vertical distribution of the aerosols is characterized as the steep decrease with altitude nearly exponentially up to 2–3 km during the northeast (NE) monsoon and winter seasons mainly dominated by clear marine and polluted continental aerosols. While it gradually decreases with altitude up to 4–5 km during pre-monsoon and southwest monsoon (SW) seasons mainly dominated by dust aerosols. The mean aerosol loadings near the surface are ~0.38 km−1 during NE monsoon and winter, ~0.30 km−1 pre-monsoon, and 0.22 km−1 during SW monsoon seasons. Such difference in the seasonal distribution of aerosol loading is mainly attributed to the difference in surface insolation, convection, long-range transport, and the atmospheric boundary layer (ABL) structure and dynamics. The ABL contributes 61%, 46%, 38%, and 63% of the overall aerosol optical depth (AOD) during the winter, pre-monsoon, SW monsoon, and NE monsoon seasons, respectively. The AOD shows a substantial seasonal variation with two local maxima during May and October and minima during January and July. The maximum and minimum AOD is found to be ~0.59 ± 0.16 and 0.4 ± 0.05, respectively. The Angstrom exponent (AE) (fine mode fraction (FMF)) shows a marked seasonal variation with a maximum value of 0.84 (0.60), indicating the dominance of finer particles during winter and minimum value of 0.54 (0.27), indicating dominance coarse particles during SW monsoon. The AE and UV aerosol index values suggest that Kattankulathur is mainly characterized by large-sized absorbing aerosols (30%) such as dust mixture and sea salt particles. Small-sized non-absorbing aerosols such as biogenic aerosols are rarely (

In this paper, we present validation of the cloud aerosol lidar with orthogonal polarization (CALIOP) level 1 and level 2 tropospheric aerosols products in coincidence to Micro Pulse Lidar (MPL) observations under different sky conditions and different seasons during March 2016–December 2018 over a tropical coastal station Kattankulathur (12.83oN, 80.04oE). In total, 33 simultaneous profiles during clear-sky (18 cases) and cloudy (15 cases; 7 mid-tropospheric (MT) clouds and 8 cirrus clouds cases) conditions are observed, out of which 5, 13, 6, and 9 cases are during winter, pre-monsoon, southwest (SW) monsoon and northeast (NE) monsoon seasons, respectively. CALIOP underestimates MPL within the boundary layer and overestimates in the free troposphere during both the clear-sky and cirrus conditions. In the clear-sky conditions, the mean bias of the level 1 aerosol products is found to be −14 ± 29% (18 ± 19%) below 3.0 km (over 3–10 km) while it is −39 ± 26% (33 ± 24%) below 3.0 km (over 3–8 km) underlying the cirrus clouds. The comparison underlying the thick MT clouds is not reliable. However, a better comparison is observed in the cases of thin MT clouds. A strong seasonal variation in the vertical distribution of the aerosol loadings near the surface with maximum (minimum) loading ~0.01 ± 0.005 km−1sr−1 (~0.004 ± 0.002 km−1sr−1) is observed during the winter (SW monsoon) season. The mean bias of level 2 aerosol profiles over the altitude 0.3–5 km is found to be 14 ± 28 % , 15 ± 44 % , −14 ± 25 % , and 24 ± 34% during the winter, pre-monsoon, SW monsoon, and NE monsoon seasons, respectively.

The diurnal variation of atmospheric boundary layer (ABL) height is studied using high-resolution radiosonde observations available at 3 h intervals for 3 days continuously from 34 intensive campaigns conducted during the period December 2010–March 2014 over a tropical station Gadanki (13.5° N, 79.2° E; 375 m), in the Indian monsoon region. The heights of the ABL during the different stages of its diurnal evolution, namely, the convective boundary layer (CBL), the stable boundary layer (SBL), and the residual layer (RL) are obtained to study the diurnal variabilities. A clear diurnal variation is observed in 9 campaigns out of the 34 campaigns. In 7 campaigns the SBL did not form in the entire day and in the remaining 18 campaigns the SBL formed intermittently. The SBL forms for 33–55 % of the time during nighttime and 9 and 25 % during the evening and morning hours, respectively. The mean SBL height is within 0.3 km above the surface which increases slightly just after midnight (02:00 IST) and remains almost constant until the morning. The mean CBL height is within 3.0 km above the surface, which generally increases from morning to evening. The mean RL height is within 2 km above the surface which generally decreases slowly as the night progresses. The diurnal variation of the ABL height over the Indian region is stronger during the pre-monsoon and weaker during winter season. The CBL is higher during the summer monsoon and lower during the winter season while the RL is higher during the winter season and lower during the summer season. During all the seasons, the ABL height peaks during the afternoon (∼ 14:00 IST) and remains elevated until evening (∼ 17:00 IST). The ABL suddenly collapses at 20:00 IST and increases slightly in the night. Interestingly, it is found that the low level clouds have an effect on the ABL height variability, but the deep convective clouds do not. The lifting condensation level (LCL) is generally found to occur below the ABL for the majority of the database and they are randomly related.

The global temperature responses to the eruptions of Mount Agung in 1963, El Chichón in 1982, and Mount Pinatubo in 1991 are investigated using nine currently available reanalysis data sets (JRA-55, MERRA, ERA-Interim, NCEP-CFSR, JRA-25, ERA-40, NCEP-1, NCEP-2, and 20CR). Multiple linear regression is applied to the zonal and monthly mean time series of temperature for two periods, 1979–2009 (for eight reanalysis data sets) and 1958–2001 (for four reanalysis data sets), by considering explanatory factors of seasonal harmonics, linear trends, Quasi-Biennial Oscillation, solar cycle, and El Niño Southern Oscillation. The residuals are used to define the volcanic signals for the three eruptions separately, and common and different responses among the older and newer reanalysis data sets are highlighted for each eruption. In response to the Mount Pinatubo eruption, most reanalysis data sets show strong warming signals (up to 2–3 K for 1-year average) in the tropical lower stratosphere and weak cooling signals (down to −1 K) in the subtropical upper troposphere. For the El Chichón eruption, warming signals in the tropical lower stratosphere are somewhat smaller than those for the Mount Pinatubo eruption. The response to the Mount Agung eruption is asymmetric about the equator with strong warming in the Southern Hemisphere midlatitude upper troposphere to lower stratosphere. Comparison of the results from several different reanalysis data sets confirms the atmospheric temperature response to these major eruptions qualitatively, but also shows quantitative differences even among the most recent reanalysis data sets. The consistencies and differences among different reanalysis data sets provide a measure of the confidence and uncertainty in our current understanding of the volcanic response. The results of this intercomparison study may be useful for validation of climate model responses to volcanic forcing and for assessing proposed geoengineering by stratospheric aerosol injection, as well as to link studies using only a single reanalysis data set to other studies using a different reanalysis data set.

The impact of the recent minor volcanic eruptions during 2001–2010 in the temperature of the upper troposphere and lower stratosphere (UTLS) is investigated using data from the Global Positioning System Radio Occultation (GPS RO), three radiosonde compilations and two reanalyses (ERA-Interim and MERRA). The volcanic signals are identified in the residual temperature time series after removal of the linear trend, the quasi-biennial oscillation and El Nino Southern Oscillation components. Eight minor volcanic eruptions (six from the tropics and two from midlatitude) over the last decade (2001–2010) are analyzed in this study. We found significant volcanic signals in the UTLS temperature only in association with the tropical Soufriere Hills and Tavurvur eruptions (in May 2006 and in October 2006, respectively). Other four tropical eruptions had very small aerosol perturbations and did not show any significant UTLS temperature change. Out of the two midlatitude eruptions, Sarychev peak had similar stratospheric aerosol perturbations as Soufriere Hills and Tavurvur eruptions, but did not show any significant UTLS temperature change. The volcanic signals in the UTLS temperature from the tropical Soufriere Hills and Tavurvur eruptions were observed for the period of 7 months after August 2006. A warming of 0.5–0.8 K in the tropical 16–18.5 km (100–70 hPa) layer was observed in association with these two tropical eruptions.

15th MST Radar WorkshopSession M6: Middle atmosphere dynamics and structureMay 30 (Tue), Poster Session

In a previous work (Mehta et al., 2011. J. Geophys. Res. 116, D20105, doi:10.1029/2011JD016637), we emphasized the limitations of the WMO definition of multiple tropopauses (MTs) which was based on the lapse rate in identifying them sometimes, and provided an alternate method called cold point method, to delineate the MTs over the tropics effectively. In the present work we described the detailed characteristics of the MTs over the tropics identified using the cold point method. We have used COSMIC GPS RO data obtained during August 2006–August 2008 and radiosonde data from 5 stations during 1999–2008 in the ±15° latitude for the present study. There is a marked latitudinal variation within the tropics in the MTs and cold point tropopause (CPT) in different seasons. These MTs can occur both above and below the CPT. The saturation water vapor mixing ratio corresponding to the lower tropopause (MTs which occur below CPT) from November to May is in general ∼3 ppmv indicating dry conditions even below the CPT altitude. The latitudinal variation of altitudes of the MTs and CPT showed quite different features. We also examined the role of equatorial waves in the occurrence of MTs. This wave mechanism could explain the MT occurrences that are in groups but not in the individual cases suggesting other mechanisms could also exist.

To investigate the sub-daily variation in Tropical Easterly Jet (TEJ), a few special experiments have been conducted with mesosphere–stratosphere–troposphere (MST) radar located at Gadanki(13.5°N, 79.2°E) under Study on Atmospheric Forcing and Responses (SAFAR) campaign during 2008–2009. Large sub-daily changes in the TEJ characteristics are observed within a day in addition to day-to-day changes. Based on this observational study, three possible mechanisms for the sub-daily variations are proposed i.e., (1) motion of TEJ core, (2) large updrafts and downdrafts, and (3) strong wave activity. Interestingly, TEJ peak altitude is seen above the Cold Point Tropopause altitude for about 42% of the days.

Association between semitransparent cirrus (STC) and tropospheric dynamics during the two contrasting seasons (Summer-monsoon and Winter) is studied using lidar and MST radar observations at Gadanki (13.5°N, 79.2°E) along with data from Geo-stationary satellite (KALPANA-1). The tropical tropopause layer (TTL) is found to be very conducive for the formation of STC. For those thicker STCs forming within TTL, the cloud top remains mostly steady with the top of the TTL, while the cloud base varies significantly in accordance with the altitude extent of tropospheric convective outflow. Based on depolarization characteristics of STCs (from lidar) along with regional distribution of tropospheric clouds derived from satellite data, altitude profile of horizontal wind, wind field at 150 hPa and air mass back trajectories, it can be reasonably inferred that, while the multi-layered and highly structured STCs during the monsoon period originate mostly from the deep convections, the sub-visual/ultra thin STCs during winter could mostly be of in situ origin.

[1] New criteria for the identification of multiple tropopauses (MTs) in the tropics are proposed using COSMIC GPS RO data during 2006–2008 in the tropical belt (±30° latitude) and radiosonde data from 5 tropical stations during 1999 to 2008 in the ±15° latitude. In the present study, we emphasized that many times the WMO definition is not able to identify all the complex structures, such as MTs, and developed alternate criteria to delineate the MTs over the tropics effectively. The new criteria are based on the cold point tropopause (CPT) and its neighborhood points of inflection in the temperature profile rather than on lapse rate, which is used in the WMO definition. The method using the new criteria (called the cold point method) identifies MTs that occur below (referred to as Lower Tropopause, LT) and above (referred to as Second Tropopause, ST; and Third Tropopause, TT) the CPT. The percentage occurrences of MTs determined using the cold point method differ from those found using the WMO definition. The percentage occurrence of MTs within the tropics maximizes at the equator, reaching higher values in the northern hemisphere (NH) summer and lower values in the NH winter. Among the MTs, the percentage occurrence of the ST is the highest, followed by that of the LT. The percentage occurrence of MTs within the tropics also shows large longitudinal variability.

[1] Extensive observations on various atmospheric parameters were carried out from Gadanki (13.48°N, 79.18°E), a tropical station in India, during the annular solar eclipse of 15 January 2010. In the present study, we report changes observed in temperature and ozone concentration in the lower stratosphere associated with the eclipse. Unusual enhancements in the temperature of 12.5 K and in ozone concentration of 5.5. mPa are observed around 21 km just after the eclipse. Plausible mechanisms for the observed eclipse effects are discussed using data of simultaneous vertical and horizontal winds collected through co-located MST radar observations. From the preliminary analysis, the temperature and ozone enhancements are attributed to large subsidence and horizontal advection, respectively.

[1] In this study, we have examined the characteristics of high-frequency gravity waves (5–50 min periodicity) over a tropical region using the mesosphere-stratosphere-troposphere (MST) radar installed at Gadanki (13.5°N, 79.2°E), India. The MST radar (53 MHz) was operated continuously for ∼15.5 h during 1700–0840 LT on 2–3 June 2005. During this period, a strong unstable wind shear region existed above the tropical easterly jet at the height of tropopause. This has provided an excellent opportunity to study the characteristics of internal atmospheric high-frequency (∼15–40 min periodicity) gravity waves, generated in the boundary layer and passing through the shear layer. The study reveals the generation of higher-frequency (5–15 min periodicity) gravity waves from this strong shear region and their vertical propagation both below up to a few kilometers and above the shear layer (∼0.5 km thick). These waves showed upward propagation even above 20 km in the lower stratosphere, indicating that unstable shear layers are the important source of momentum and energy fluxes that contribute significantly to the middle atmospheric dynamics in terms of gravity waves. Further, a close association was also observed between the dissipating gravity waves and the distinctly enhanced signal-to-noise ratio and Doppler spectral width of the MST radar echoes. The present observation of radiation of high-frequency gravity waves that propagate vertically upward from a strong wind shear region located immediately below a highly stratified layer is in accordance with the “direct mechanism” explained by nonlinear numerical simulation studies. For the first time, the present study illustrates the existence of layers of polarized refractive index structures in the heights of 10–15 km.

[1] The variations of the cold point tropopause (CPT), convective tropopause (COT), lapse rate tropopause (LRT), and tropical tropopause layer (TTL) from subdaily to seasonal timescales are studied using high-resolution radiosonde observations from April 2006 to December 2008 over a tropical station Gadanki (13.5°N, 79.2°E), in the Indian monsoon region. The correlations between temperatures and altitudes of the different tropopauses and between TTL thickness and satellite brightness temperature (TBB) are estimated. Diurnal behavior of CPT, LRT, and COT is also investigated. The seasonal variation of the CPT at Gadanki shows notable differences when compared to Western Pacific region, though major features remain similar. CPT temperature at Gadanki goes below 191 K more frequently during December to May than during June to November. The TTL thickness, which is the difference between CPT altitude and COT altitude, is small during summer monsoon and is strongly correlated with TBB on seasonal scale. The CPT altitude and temperature show large variation by as much as ∼1 km and ∼3 K, respectively, even on subdaily scale. During deep convection (TBB 240), increase in the CPT altitude with increase in CPT temperature is noticed on some occasions. Strong correlation between LRT (and COT) altitude and temperature from subdaily to seasonal timescale is noticed in contrast to CPT altitude and temperature. However, the correlation between TBB and CPT, LRT, and COT degrades from seasonal to subdaily timescale.

[1] Satellite observations of brightness temperature in the atmospheric window and water vapor bands are widely used for studying the regional/global distribution of semi-transparent cirrus (STC). The present study provides the first quantitative assessment of the lower limit of cloud optical depth (COD) of STC that can be detected using this method and the conditions under which these observations are reliable, by comparing the STC information derived from the Very High Resolution Radiometer (VHRR) onboard the Indian geostationary satellite KALPANA-1 over the tropical station Gadanki (13.5°N, 79.2°E) with cirrus COD obtained from collocated Lidar observations for 12 nights during different seasons under contrasting cloud conditions. Satellite-derived STC amount is found to be highly reliable when COD > 0.02 and is an underestimate when it decreases below 0.02, especially when they appear as broken clusters. However, in most of the cases, satellite could detect very thin STC with COD < 0.02 when they are widespread.

[1] In this paper, it is shown that the altitude of the tropopause can be determined directly from the profile of Bending Angle (α) of GPS RO (hereafter called as Radio Tropopause, RT) instead of from the derived parameter of temperature which needs further assumptions like hydrostatic equilibrium. Above the altitude range of moist atmosphere, the altitude of peak in α′(=dα/dh) profiles above which it decreases for at least 1 km is defined as the RT. The RT altitude is compared with the cold point tropopause (CPT)/lapse rate tropopause (LRT) altitude from independent measurements of temperature by the radiosonde at different stations. A very good agreement is observed between the tropopause altitudes from these two independent techniques. Particularly at polar latitudes, where it is often difficult to identify the tropopause altitude from temperature profiles, the present method is a more reliable means of identifying the tropopause.

Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC), consisting of six Low Earth Orbit (LEO) Global Position System (GPS) receivers, on board the Formosat Satellite 3 (FORMOSAT-3) is providing dense observations of density, refractivity, temperature and water vapor profiles of the neutral atmosphere since middle of July 2006. Special radiosonde (Väisälä) campaign was conducted at Gadanki (13.48°N, 79.18°E), a tropical site in India, during July 2006 to March 2007 to validate these meteorological parameters. Co-located Nd: YAG Rayleigh lidar was also operated during the overpass of COSMIC and is utilized to validate the temperatures in the height range of 30 to 40 km. Atotal of 142 overpasses occurred during the above mentioned period within 300 km distance from Gadanki out of which 41 overpasses occurred within a time difference of ±4 hours of radiosonde launch. In addition, 18 overpasses occurred within the time difference of ±4 hours of lidar operation. A detailed comparison has been made with all these overpasses for the refractivity, temperature and water vapor obtained from COSMIC. The water vapor comparison has shown generally a good agreement with a mean difference of 5 - 10% below 6 - 7 km. Although there is a colder bias between COSMIC and radiosonde, a very good comparison in temperature is also found between 10 and 27 km with a mean difference of less than 1 K (RMS difference is only 0.64 K). There exists a large difference in temperature of about 8 K between 30 and 40 km (between COSMIC and lidar). Possible reasons for these large differences are given. There was one event that occurred just over Gadanki for which a detailed comparison has been made with special emphasis on water vapor retrievals. Sensitivity test is also done on the fractional difference in N for the event that occurred on 24 July 2006 between COSMIC (1D-var) and radiosonde and found that pressure plays a key role than temperature in determining the refractivity.

[1] Using the MST radar observations at Gadanki (13.5°N, 79.2°E), a tropical station, the altitude of major convective outflow in the troposphere is identified and is considered to represent the convective tropopause. This is found to match well with the altitude of local minimum of potential temperature lapse rate obtained from simultaneous radiosonde observations. The convective tropopause altitudes are also compared with the cloud top altitudes obtained using satellite brightness temperature (BT) data and are found to match in the case of deep convection. The thickness of the tropical tropopause layer follows very closely the convective tropopause altitude and has little dependence on the cold point tropopause altitude. The thickness of the tropopause layer is found to shrink when convection reaches high altitudes. This occurs mainly during the monsoon months of July, September, and October.