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Article Type:
Research Article

Intriguing Aspects of the Monsoon Low-Level Jet over Peninsular India Revealed by High-Resolution GPS Radiosonde Observations

M. Roja Raman Department of Physics, Sri Venkateswara University, Tirupati, India

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M. Venkat Ratnam National Atmospheric Research Laboratory, Gadanki, Tirupati, India

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M. Rajeevan National Atmospheric Research Laboratory, Gadanki, Tirupati, India

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V. V. M. Jagannadha Rao SRRS Government Polytechnic, Sircilla, India

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S. Vijaya Bhaskara Rao Department of Physics, Sri Venkateswara University, Tirupati, India

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Print Publication:
01 Jul 2011
DOI:
https://doi.org/10.1175/2011JAS3611.1
Page(s):
1413–1423
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Abstract

The strong cross-equatorial flow in the lower troposphere, widely known as the monsoon low-level jet (MLLJ), plays an important role in the Indian summer monsoon (ISM) rainfall during June–September. Using high-resolution GPS radiosonde observations over Gadanki (13.5°N, 79.2°E), some new aspects of MLLJ have been reported. In the present study it is found that, on average, the MLLJ exists at 710 hPa over southeastern peninsular India, rather than at 850 hPa as reported by earlier studies. It is observed that the ECMWF Re-Analysis (ERA)-Interim data provide better results on the spatial, temporal, and vertical variation of MLLJ. Further, the characteristics of the MLLJ during the active and break spells of ISM are also investigated; higher MLLJ core height and intensity are found during active phases of the Indian monsoon. This study emphasizes the use of high-resolution measurements for studying monsoon dynamics in detail.

Corresponding author address: Dr. M. Venkat Ratnam, National Atmospheric Research Laboratory, Department of Space, Gadanki, Post Box 123, Tirupati 517 502, India. E-mail: vratnam@narl.gov.in

Abstract

The strong cross-equatorial flow in the lower troposphere, widely known as the monsoon low-level jet (MLLJ), plays an important role in the Indian summer monsoon (ISM) rainfall during June–September. Using high-resolution GPS radiosonde observations over Gadanki (13.5°N, 79.2°E), some new aspects of MLLJ have been reported. In the present study it is found that, on average, the MLLJ exists at 710 hPa over southeastern peninsular India, rather than at 850 hPa as reported by earlier studies. It is observed that the ECMWF Re-Analysis (ERA)-Interim data provide better results on the spatial, temporal, and vertical variation of MLLJ. Further, the characteristics of the MLLJ during the active and break spells of ISM are also investigated; higher MLLJ core height and intensity are found during active phases of the Indian monsoon. This study emphasizes the use of high-resolution measurements for studying monsoon dynamics in detail.

Corresponding author address: Dr. M. Venkat Ratnam, National Atmospheric Research Laboratory, Department of Space, Gadanki, Post Box 123, Tirupati 517 502, India. E-mail: vratnam@narl.gov.in
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