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<p>The signatures of Madden–Julian oscillation (MJO) in the intraseasonal variation of cirrus occurrence and dehydration in the upper troposphere and lower stratosphere (UTLS) over Indian region is examined using satellite and reanalysis datasets. The occurrence of deep convection shows a clear intraseasonal variation over the Indian region with peak occurrence during the second and third phase of MJO. A clear cooling is observed in these phases over regions of occurrence of deep convection over the southern Indian peninsula and equatorial Indian Ocean in winter, pre-monsoon and post- monsoon seasons. The higher occurrence frequency of water vapour mixing ratio (WVMR) &lt; 3&#xa0;ppmv at 121&#xa0;hPa and 100&#xa0;hPa confirms the occurrence of dehydration in the tropical tropopause layer (TTL) during these phases with the region of peak occurrence of deep convection showing an eastward shift with eastward propagation of MJO. The occurrence of cirrus clouds shows a clear variation with the different phases of MJO. The occurrence frequency of cirrus clouds is maximum with a peak occurrence of 60% in phases 2 and 3 of MJO over the southern Peninsular India and adjoining oceanic region in all the seasons except summer monsoon season. The thickness of cirrus almost doubles in the convective phases of MJO (phases 2 and 3 over Indian Peninsula) when compared to non-convective phases of MJO. There is a significant connection between occurrence of multilayer cirrus and dehydration within the TTL. However, direct connection between MJO phases and occurrence of cirrus clouds is not observed in the summer monsoon season due to widespread occurrence of cirrus clouds all over the Indian region in this season.</p>

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Signatures of MJO in the intra-seasonal variability in occurrence of cirrus and dehydration in the UTLS over Indian region

  • 期刊论文

  • 发表日期：

    2025年12月19日

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  • Maria Emmanuel,
  • K. Satheesan,
  • Ajil Kottayil

摘要

The signatures of Madden–Julian oscillation (MJO) in the intraseasonal variation of cirrus occurrence and dehydration in the upper troposphere and lower stratosphere (UTLS) over Indian region is examined using satellite and reanalysis datasets. The occurrence of deep convection shows a clear intraseasonal variation over the Indian region with peak occurrence during the second and third phase of MJO. A clear cooling is observed in these phases over regions of occurrence of deep convection over the southern Indian peninsula and equatorial Indian Ocean in winter, pre-monsoon and post- monsoon seasons. The higher occurrence frequency of water vapour mixing ratio (WVMR) < 3 ppmv at 121 hPa and 100 hPa confirms the occurrence of dehydration in the tropical tropopause layer (TTL) during these phases with the region of peak occurrence of deep convection showing an eastward shift with eastward propagation of MJO. The occurrence of cirrus clouds shows a clear variation with the different phases of MJO. The occurrence frequency of cirrus clouds is maximum with a peak occurrence of 60% in phases 2 and 3 of MJO over the southern Peninsular India and adjoining oceanic region in all the seasons except summer monsoon season. The thickness of cirrus almost doubles in the convective phases of MJO (phases 2 and 3 over Indian Peninsula) when compared to non-convective phases of MJO. There is a significant connection between occurrence of multilayer cirrus and dehydration within the TTL. However, direct connection between MJO phases and occurrence of cirrus clouds is not observed in the summer monsoon season due to widespread occurrence of cirrus clouds all over the Indian region in this season.