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<p>The monsoon inversion (MI) layer over the western part of the Arabian Sea (AS) from June to September serves as one of the semi-permanent features of the Indian summer monsoon which plays an essential role in pollution dispersion and exchange between the atmospheric boundary layer (ABL) and free troposphere (FT). The analysis focuses on characterizing the inversion layers over Salalah (17.0<sup>o</sup>N, 54.1<sup>o</sup>E), a station on the west coast of the AS, using radiosonde and Indian monsoon data assimilation and analysis (IMDAA) datasets at 00 UTC during 2016–2020. The ABL over Salalah at 00 UTC is characterized as the stable boundary layer (SBL) at ~ 0.3 ± 0.15&#xa0;km and residual layer (RL) at ~ 1.25 ± 0.35—1.5 ± 0.4&#xa0;km from October to May while and MI layer at ~ 1.25 ± 0.25&#xa0;km during June to September. MI strength highly varies on a day-to-day scale which is characterized into five different categories based on the temperature change (ΔT) between the 950 and 850&#xa0;hPa levels. The threshold limit ΔT &gt; 2.7&#xa0;K, 2.7 ≥ ΔT &gt; 0&#xa0;K, 0 ≥ ΔT &gt; − 2.5&#xa0;K, − 2.5 ≥ ΔT &gt; − 5&#xa0;K, and ΔT ≤ − 5&#xa0;K signifies the different categories C<sub>1</sub>, C<sub>2</sub>, C<sub>3</sub>, C<sub>4,</sub> and C<sub>5</sub>, respectively that are found to be 14% (2%), 9% (10%), 16% (23%), 29% (43%), and 32% (22%) out of 586 (610) radiosonde (IMDAA) profiles from June- September during 2016–2020. The strength and thickness of the MI increase from the C<sub>1</sub> to C<sub>5</sub> categories. The mean temperature and relative humidity profiles of these categories reveal that the stronger the MI, the shallower it is and the drier the layer aloft and vice versa. The advective term indicates warm advection below MI layer and cold advection aloft it which becomes stronger with increasing horizontal windspeed from C<sub>1</sub> to C<sub>5</sub> categories. The convective term indicates warm air within the MI layer overlaid by the cold subsiding air which remains sustained almost equally for the different categories. The saturation pressure deficit suggests the cloudy layer below the MI whose extension decreases from C<sub>1</sub> to C<sub>5</sub>. It is observed that MI and FT almost contribute equally to the total integrated water vapor essential for cloud formation.</p>

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Meteorological conditions associated with different categories of monsoon inversions over Salalah (17.0° N, 54.1° E), a station on the west coast of the Arabian Sea

  • 期刊论文

  • 发表日期：

    2025年6月14日

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  • Sanjay Kumar Mehta,
  • Sachin Philip Kakkanattu

摘要

The monsoon inversion (MI) layer over the western part of the Arabian Sea (AS) from June to September serves as one of the semi-permanent features of the Indian summer monsoon which plays an essential role in pollution dispersion and exchange between the atmospheric boundary layer (ABL) and free troposphere (FT). The analysis focuses on characterizing the inversion layers over Salalah (17.0oN, 54.1oE), a station on the west coast of the AS, using radiosonde and Indian monsoon data assimilation and analysis (IMDAA) datasets at 00 UTC during 2016–2020. The ABL over Salalah at 00 UTC is characterized as the stable boundary layer (SBL) at ~ 0.3 ± 0.15 km and residual layer (RL) at ~ 1.25 ± 0.35—1.5 ± 0.4 km from October to May while and MI layer at ~ 1.25 ± 0.25 km during June to September. MI strength highly varies on a day-to-day scale which is characterized into five different categories based on the temperature change (ΔT) between the 950 and 850 hPa levels. The threshold limit ΔT > 2.7 K, 2.7 ≥ ΔT > 0 K, 0 ≥ ΔT > − 2.5 K, − 2.5 ≥ ΔT > − 5 K, and ΔT ≤ − 5 K signifies the different categories C1, C2, C3, C4, and C5, respectively that are found to be 14% (2%), 9% (10%), 16% (23%), 29% (43%), and 32% (22%) out of 586 (610) radiosonde (IMDAA) profiles from June- September during 2016–2020. The strength and thickness of the MI increase from the C1 to C5 categories. The mean temperature and relative humidity profiles of these categories reveal that the stronger the MI, the shallower it is and the drier the layer aloft and vice versa. The advective term indicates warm advection below MI layer and cold advection aloft it which becomes stronger with increasing horizontal windspeed from C1 to C5 categories. The convective term indicates warm air within the MI layer overlaid by the cold subsiding air which remains sustained almost equally for the different categories. The saturation pressure deficit suggests the cloudy layer below the MI whose extension decreases from C1 to C5. It is observed that MI and FT almost contribute equally to the total integrated water vapor essential for cloud formation.