Vicinity Of Tropopause Research Articles

Multiplatform observations of stratosphere-troposphere exchange over the Bharati (69.41° S, 76° E), Antarctica during ISEA-35

This paper deals with the observations of stratospheric ozone intruding into the troposphere over the Bharati (69.41° S, 76.19° E) station in Antarctica, made during 35th Indian Scientific Expeditions to Antarctica (ISEA-35) during jet stream conditions. High-resolution multiplatform measurements from radiosonde coupled with ozonesonde, Very High-Frequency (VHF) radar and Micro-Limb Sounder (MLS) and Indian National Satellite System (INSAT-3D) satellite measurements are used for the present study. The most significant observation is that there is an increase of ozone by 30 ppbv in the upper troposphere and decrease by 100–110 ppbv in the lower stratosphere and this condition persisted for three successive days. The wind shows the presence of jet-stream in the vicinity of tropopause, enhancing the turbulence due to wind shear during the event of stratospheric intrusion. Further, the vertical velocity shows the presence of strong updrafts and downdrafts in the vicinity of tropopause which manifests the tropopause oscillation. Global analysis of satellite and reanalysis data also indicates the horizontal intrusion of stratospheric air from the mid-latitude to upper troposphere over the Bharati station. These observations constitute the first multi-instrumented, experimental evidence of stratospheric intrusions over the coastal Antarctica. These results are presented and discussed in the light of present understanding of turbulence and tropopause oscillation.

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.

Aerosol characteristics in the upper troposphere and lower stratosphere region during successive and contrasting Indian summer monsoon season

Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO)-derived aerosol vertical profiles were studied in the upper troposphere and lower stratosphere (UTLS) over the Indian summer monsoon (ISM) region during two successive and contrasting monsoon years (2008–2009). An enhanced aerosol layer was observed in the UTLS between 15 and 19 km altitude, in the vicinity of tropopause during both years. However, the optical characteristics of aerosol layers were found to be dissimilar during the two contrasting consecutive summer monsoon seasons. While the depolarization ratio of enhanced aerosol layer (exceeding 0.2) during both years suggested anisotropic nature of particles, the aerosol backscatter coefficient was observed to be more intensified with a sharp peak during the active monsoon year (2008) whereas it was relatively broader with lower magnitude during a drought year (2009). The enhanced backscatter coefficient in the UTLS was found to be closely associated with the variability in tropopause height and convection during both years, which is more pronounced during the active monsoon year as compared to a drought year. Deep convection over the ISM region may inject boundary layer aerosols into the upper troposphere as evidenced from the analysis of the outgoing long-wave radiation (OLR). Our results also showed an enhanced integrated backscatter coefficient (IBC) of about 30%, which is associated with a decrease in OLR of about 7% during the active monsoon year as compared to drought year. These findings were further corroborated using NCEP-NCAR vertical velocity and HYSPLIT air-mass backward trajectory analyses.

Stratospheric intrusion into the troposphere during the tropical cyclone Nilam (2012)

This article discusses different plausible mechanisms to account for the intrusion of dry ozone‐rich stratospheric air into the troposphere during the passage of the tropical cyclone Nilam‐2012. The present study shows that the overshooting convection associated with Nilam is found to be the prime candidate for the generation of turbulence in the vicinity of tropopause (VOT). In addition, the presence of strong updraughts and downdraughts in the VOT weakened the stability of the tropopause which allowed the dry ozone‐rich stratospheric air to penetrate downwards to the troposphere. Significant modulation of the tropopause structure is observed which is found to be accompanied by structures linked with shear instability. Concurrent ozone measurements also indicate the intrusion of stratospheric air mass into the upper and middle troposphere.

Aerosol characteristics in the UTLS region: A satellite-based study over north India

Abstract Vertical profiles of aerosol backscatter coefficient and depolarization ratio, obtained from the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite, were studied in the upper troposphere and lower stratosphere (UTLS) region over North India (21–30° N and 72–90° E), covering the highly polluted Indo-Gangetic Plain (IGP) for one-year period from December 2011 to November 2012. An enhanced aerosol layer was observed between 15 and 18 km altitude, in the vicinity of tropopause, with a broad layer depth of about 2 km. The aerosol layer showed strong seasonal, monthly as well as day and night time variability, with a peak value of backscatter coefficient during monsoon season (∼5.54 × 10−3 sr−1 in September). The corresponding depolarization ratio indicates anisotropic (non-spherical) nature of particles. The aerosol layer was found to be highly linked with the variability in tropopause height, showing a positive correlation between tropopause height and the height of maximum backscatter coefficient (correlation coefficient of 0.8). However, it was found to be negatively correlated with the integrated backscatter coefficient (IBC), with a correlation coefficient of 0.3. We further analyzed outgoing long-wave radiation (OLR) data during the study period to investigate the link between the observed enhanced aerosol layer in the UTLS region and prevailing deep convective activities over the study region. Low values of OLR during monsoon (about 214 W m−2) indicate the occurrence of deep convection over this region, which may cause a large-scale circulation-driven vertical transport of boundary-layer pollution into the atmosphere of UTLS region. Results may have potential implications for better understanding and assessing the chemical and radiative impacts of these aerosols in the tropical UTLS region.

Characteristics of gravity waves generated in a convective and a non-convective environment revealed from hourly radiosonde observation under CPEA-II campaign

Abstract. Analyses of hourly radiosonde data of temperature, wind, and relative humidity during four days (two with convection and two with no convection) as a part of an intensive observation period in CPEA-2 campaign over Koto Tabang (100.32° E, 0.20° S), Indonesia, are presented. Characteristics of gravity waves in terms of dominant wave frequencies at different heights and their vertical wavelengths are shown in the lower stratosphere during a convective and non-convective period. Gravity waves with periods ~10 h and ~4–5 h were found dominant near tropopause (a region of high stability) on all days of observation. Vertical propagation of gravity waves were seen modified near heights of the three identified strong wind shears (at ~16, 20, and 25 km heights) due to wave-mean flow interaction. Between 17 and 21 km heights, meridional wind fluctuations dominated over zonal wind, whereas from 22 to 30 km heights, wave fluctuations with periods ~3–5 h and ~8–10 h in zonal wind and temperature were highly associated, suggesting zonal orientation of wave propagation. Gravity waves from tropopause region to 30 km heights were analyzed. In general, vertical wavelength of 2–5 km dominated in all the mean-removed (~ weekly mean) wind and temperature hourly profiles. Computed vertical wavelength spectra are similar, in most of the cases, to the source spectra (1–16 km height) except that of zonal wind spectra, which is broad during active convection. Interestingly, during and after convection, gravity waves with short vertical wavelength (~2 km) and short period (~2–3 h) emerged, which were confined in the close vicinity of tropopause, and were not identified on non-convective days, suggesting convection to be the source for them. Some wave features near strong wind shear (at 25 km height) were also observed with short vertical wavelengths in both convective and non-convective days, suggesting wind shear to be the sole cause of generation and seemingly not associated with deep convection below. A drop in the temperature up to ~4–5 K (after removal of diurnal component) was observed at ~16 km height near a strong wind shear (~45–55 m s−1 km−1) during active period of convection.

VHF radar echoes in the vicinity of tropopause during the passage of tropical cyclone: First observations from the Gadanki MST radar

First observations on the characteristics of VHF radar echoes in the vicinity of tropopause (VOT) during depression or passage of tropical cyclone made using the Gadanki MST radar are presented. The most significant and new observation is that signal‐to‐noise ratio (SNR) in zenith and off‐zenith beams are nearly equal in the VOT when a cyclone is located close to the radar site. During depression, however, a slight decrease in echo strength with zenith angle was found. Observations made during such disturbed conditions are in contrast to the usual aspect‐sensitive characteristics of the radar echoes. Spectral widths during disturbed atmospheric conditions in general are found to be much larger than that of normal condition. Further, spectral widths observed in the vertical beam during cyclone are considerably larger than that during normal condition. These features, however, have not been noticed at other height regions during such atmospheric conditions. All these observations clearly indicate preferential enhancement in turbulence activity in the VOT. These observations constitute the first experimental evidence of such a zenith angle dependence of VHF radar echo characteristics in the VOT during depression and cyclone. These results are presented and discussed in the light of present understanding of turbulence activity in the VOT.