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Title: Some Characteristics of Zonal Wind in the Middle Atmosphere Over India
Authors: Kumar, Somesh
Nagpal, O P
Issue Date: Dec-1987
Publisher: NISCAIR-CSIR, India
Abstract: Monthly averaged values of the tropospheric and lower stratospheric wind fields for 15 months period May 1982-July 1983 obtained by high altitude balloons at ten Indian stations, along with the rocket observed winds for the parallel period (1982-83) at two rocket ranges in the country are analyzed to obtain the height-latitude and time variation of zonal winds over Indian region, encompassing a latitude range of 8-28°N. The monthly mean values are also used to bring out the amplitudes and phases of the semi-annual oscillation (SAO) and annual oscillation (AO), thus providing an opportunity to obtain a first ever picture of their latitudinal variations. Similarly, a study of quasi-biennial oscillation (QBS) is made with the help of 7-year data (1977-83) at Hyderabad station (17.2°N, 78.3°E). Results show that there is easterly flow during summer months. between 10 and 15 km with a strong easterly jet of 50-60 m/s at tropopause heights during monsoonal months. The winds turn to westerlies during winter months and there is an indication that this reversal starts first at high latitude stations and at lower heights and moves equatorward ascending with time to higher altitudes. The reversal of westerlies to easterlies, on the other hand, takes place at higher altitudes (~ 50 km) and at low latitudes, descending downward with time to lower levels and moving northward. The occurrence of strong tropospheric easterly jet seems to be negatively correlated with the monsoonal activity. The SAO has an amplitude of about 5 m/s or less below 30 km altitude up to about 20ᵒN latitude, increasing to 12 m/s at 26.5ᵒN at 32 km. At higher heights, its amplitude becomes significant reaching 30 m/s at 54 kmat Thumba and 20 m/s at 50 km at Balasore. The annual oscillation, on the other hand, has a well defined peak at the tropopause height at all the stations, maximizing at about 20ᵒN latitude with an amplitude of 30 m/s. The QBO at Hyderabad station has an amplitude maximum of 8 m/s at about 25 km, reducing to about 2 m/s at 17 km. The observed features of SAO, AO and QBO in zonal winds are discussed in relation to earlier observations and some significant differences noted.
Page(s): 390-400
ISSN: 0975-105X (Online); 0367-8393 (Print)
Appears in Collections:IJRSP Vol.16(6) [December 1987]

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