Editorial Type:
Article
Article Type:
Research Article

Life Cycle Characteristics of Deep Cloud Systems over the Indian Region Using INSAT-1B Pixel Data

Arvind V. Gambheer Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore, India

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G. S. Bhat Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore, India

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Print Publication:
01 Dec 2000
DOI:
https://doi.org/10.1175/1520-0493(2000)129<4071:LCCODC>2.0.CO;2
Page(s):
4071–4083
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Abstract

A detailed study of deep cloud systems (denoted by CSs) over the Indian region using INSAT-1B pixel data is presented. The life cycle characteristics of CSs are examined, including their preferred regions of formation and dissipation, frequency of occurrence, life duration, and speeds of propagation. A new automatic algorithm to track cloud systems has been developed that takes into account the mergers and splits in CSs. The algorithm is based on a combination of the maximum allowable displacement of a CS in 3 h and area overlap. The choice of the minimum size for CS is fixed at 4800 km2. The temperature threshold is varied from 201 to 261 K. It is observed that majority of CSs decay within a couple of hundred kilometers from where they form. There is a bimonthly modulation of the areal extent of more frequent convection. The number of CSs increases approximately linearly with threshold temperature up to 251 K. Tracking results are not very sensitive to the criterion chosen for identifying the successor in cases of multiple candidates, except for CSs that live longer than 36 h. Mean speeds of propagation of CSs range from 7 to 9 m s−1.

Corresponding author address: Dr. G. S. Bhat, Center for Atmospheric and Oceanic Studies, Indian Institute of Sciences, Bangalore 560 012, India.

Email: bhat@caos.iisc.ernet.in

Abstract

A detailed study of deep cloud systems (denoted by CSs) over the Indian region using INSAT-1B pixel data is presented. The life cycle characteristics of CSs are examined, including their preferred regions of formation and dissipation, frequency of occurrence, life duration, and speeds of propagation. A new automatic algorithm to track cloud systems has been developed that takes into account the mergers and splits in CSs. The algorithm is based on a combination of the maximum allowable displacement of a CS in 3 h and area overlap. The choice of the minimum size for CS is fixed at 4800 km2. The temperature threshold is varied from 201 to 261 K. It is observed that majority of CSs decay within a couple of hundred kilometers from where they form. There is a bimonthly modulation of the areal extent of more frequent convection. The number of CSs increases approximately linearly with threshold temperature up to 251 K. Tracking results are not very sensitive to the criterion chosen for identifying the successor in cases of multiple candidates, except for CSs that live longer than 36 h. Mean speeds of propagation of CSs range from 7 to 9 m s−1.

Corresponding author address: Dr. G. S. Bhat, Center for Atmospheric and Oceanic Studies, Indian Institute of Sciences, Bangalore 560 012, India.

Email: bhat@caos.iisc.ernet.in

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