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Variations of surface pressure over India during the southwest monsoon

Summary

Intraseasonal and interannual variations of surface pressure and surface pressure anomalies are studied using 19 years of daily surface pressure data at 60 stations in India during the south-west monsoon season. The interannual variability of surface pressure is highest over northwest India and a ridge runs eastward near 23 °N. The spatial pattern of total daily intra-seasonal variations is similar to that of interannual variability. The seasonal cycle accounts for about 50% of the intraseasonal variance over northwest India. When the seasonal cycle is removed the high standard deviations are observed over the area adjoining the head of the Bay of Bengal where the frequency of occurrence of the intense cyclonic disturbances is highest. The area of maximum intraseasonal variability keeps shifting westward as one goes from June through to September.

A harmonic analysis is performed to study the contribution to the variances by the 30–60 days and 10–20 days period ranges during excess and deficient monsoon years. EOF analysis of the 5-day mean pressure anomaly fields is conducted to study the most dominant modes of variation. The evolutionary features of surface pressure fields are studied with the help of Hovmöller diagrams and EEOF analysis. The relationships between westward and northward progression of anomalies and their influence on monsoon conditions is also studied.

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This paper is a part of m.sc. thesis submitted by the fist author under the guidance of the second author.

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Nagar, S.G., Singh, S.V. Variations of surface pressure over India during the southwest monsoon. Theor Appl Climatol 44, 95–112 (1991). https://doi.org/10.1007/BF00867997

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Keywords

  • Interannual Variability
  • Surface Pressure
  • Seasonal Cycle
  • Intraseasonal Variability
  • Anomaly Field