High temporal resolution VHF radar observations of stratospheric air intrusions in to the upper troposphere during the passage of a mesoscale convective system over Gadanki (13.5° N, 79.2° E)

摘要

A high temporal resolution VHF radar experiment, which was carried out todivulge the clear-air structure of a mesoscale convective system (MCS) atfine time scales over Gadanki, is discussed. The VHF radar was continuouslyoperated for four hours with 11 seconds time resolution on 19 June 2006,which facilitated the study of finer details of stratospheric air intrusionsinto the upper troposphere during the passage of a MCS. Simultaneous GPSsonde and ground based optical rain gauge measurements are also used for thepresent study along with radar observations. The height-time section ofrange corrected signal to noise ratio (RSNR) revealed the convective cellsreaching as high as 14 km altitude and the signature of the tropopause as alayered structure at around 16.5 km. The important observation from theradar RSNR is the time localized inclined echoes in the height region of12–16 km region giving evidence for stratospheric air intrusion into theupper troposphere. Further, this observation is confirmed by theheight–time section of vertical velocity, which showed the intensedowndraughts in the height region of inclined radar echoes. A detailedexamination of this down draft revealed an episode of high frequency gravitywave excitation, which is believed to be the consequence of intrusion ofstable stratospheric air into the upper troposphere. Thus, the present studybrings out for the first time, how the stratospheric intrusions will appearin the radar height-time sections and the consequences of such intrusionsin the upper troposphere