Characteristics of monsoon inversions over the Arabian Sea observed by satellite sounder and reanalysis data sets

Sanjeev Dwivedi,M Venkat Ratnam,M S Narayanan,D Narayana Rao

doi:10.5194/acp-16-4497-2016

Sanjeev Dwivedi, M Venkat Ratnam + Show 2 more

Open Access

https://doi.org/10.5194/acp-16-4497-2016

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Abstract

Abstract. Monsoon inversion (MI) over the Arabian Sea (AS) is one of the important characteristics associated with the monsoon activity over Indian region during summer monsoon season. In the present study, we have used 5 years (2009–2013) of temperature and water vapour measurement data obtained from satellite sounder instrument, an Infrared Atmospheric Sounding Interferometer (IASI) onboard MetOp satellite, in addition to ERA-Interim data, to study their characteristics. The lower atmospheric data over the AS have been examined first to identify the areas where MIs are predominant and occur with higher strength. Based on this information, a detailed study has been made to investigate their characteristics separately in the eastern AS (EAS) and western AS (WAS) to examine their contrasting features. The initiation and dissipation times of MIs, their percentage occurrence, strength, etc., has been examined using the huge database. The relation with monsoon activity (rainfall) over Indian region during normal and poor monsoon years is also studied. WAS ΔT values are ∼ 2 K less than those over the EAS, ΔT being the temperature difference between 950 and 850 hPa. A much larger contrast between the WAS and EAS in ΔT is noticed in ERA-Interim data set vis-à-vis those observed by satellites. The possibility of detecting MI from another parameter, refractivity N, obtained directly from another satellite constellation of GPS Radio Occultation (RO) (COSMIC), has also been examined. MI detected from IASI and Atmospheric Infrared Sounder (AIRS) onboard the NOAA satellite have been compared to see how far the two data sets can be combined to study the MI characteristics. We suggest MI could also be included as one of the semipermanent features of southwest monsoon along with the presently accepted six parameters.

Highlights

Monsoon inversion (MI) is one of the criteria providing a stability condition over the western Arabian Sea (AS), extending sometimes through to the west coast of India
To show the efficiency and strength of currently available satellite measurements to delineate features of MI over the AS, typical profiles of temperature and relative humidity (RH) obtained from collocated Infrared Atmospheric Sounding Interferometer (IASI) and ERA-Interim on 30 July 2009, 05:30 GMT are plotted in Fig. 1c and d, respectively
Low-level MI characteristics, which usually occur below 700 hPa over the AS during the southwest monsoon months, have been identified directly from operational satellite temperature retrievals

Summary

Introduction

Monsoon inversion (MI) is one of the criteria providing a stability condition over the western Arabian Sea (AS), extending sometimes through to the west coast of India. MI controls the midtropospheric moisture content during the different phases of the monsoon This shallow layer of low-level inversion (below ∼ 800 hPa) will act as a barrier in uplifting of the moisture, and could act like a wave guide for transport of water vapour to the mainland. Indian rainfall is dependent on the physical processes occurring over the AS like sea surface temperature (SST), Somali low-level jet stream, the advection of hot air from the Arabian Desert, etc. These have a profound effect on strength of MI. MI has been known to be intimately associated with the activity of the Indian southwest monsoon and has a close link with active and break spells (Narayanan et al, 2004)

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