The role of monsoon low‐level jet in modulating heavy rainfall events

Xavier, Anu; Kottayil, Ajil; Mohanakumar, K.; Xavier, Prince

doi:10.1002/joc.5390

Cited by 34 publications

(13 citation statements)

References 29 publications

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“…Modelling efforts using the planetary boundary layer (PBL) model (Krishnamurti et al ., ; ) have successfully reproduced observed features of the Somali jet, such as its curvature, peak intensity, and position. Many other numerical studies have reported the significance of the Somali jet as a cross‐equatorial moisture‐flux feeding mechanism for the ISM and determined its role in creating convective instabilities required for triggering heavy events over the west coast of India (Raymond, ; Xavier et al ., ).…”

Section: Introductionmentioning

confidence: 97%

Variability of monsoon low‐level jet and associated rainfall over India

Viswanadhapalli

Dasari

Dwivedi

et al. 2019

Intl Journal of Climatology

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The structure and climatology of the monsoon low‐level jet (MLLJ) is studied based on dynamically downscaled simulations over a 37‐year period (1980–2016) using the Weather Research Forecasting (WRF) model. The simulations are conducted by adopting a continuous initialization method with daily re‐initializations using ERA‐Interim data as initial and boundary conditions. Validation of the downscaled fields with radiosonde data shows that the model has reasonable skill in reproducing MLLJ characteristics. Analysis of the simulations suggests that the MLLJ exhibits systematic diurnal variation: maximum winds of the synoptically induced large‐scale monsoon jet occur during the daytime, and the orographic channelled winds through the mountains of East Africa, Hejaz, and Western Ghats in the night‐time. These diurnal changes in monsoon winds modulate the moisture convergence process and the associated evolution of rainfall over India. Seasonal and monthly climatology of monsoon winds shows that the model accurately reproduces the spatial pattern of winds and slightly overestimates (2–3 m/s) the mean monthly winds over the Bay of Bengal and Arabian Seas. Analysis of wind variability and the trends using 37 years simulations suggests that the MLLJ exhibits an increasing trend in wind speed on both seasonal and monthly scales, except for August which shows a decreasing trend. The weakening of the MLLJ in August has a profound influence on the number of monsoon depressions forming over the Bay of Bengal (which are decreasing), and on the number of break days (which are increasing) and associated precipitation reduction over the central Indian region.

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Section: Introductionmentioning

confidence: 97%

Variability of monsoon low‐level jet and associated rainfall over India

Viswanadhapalli

Dasari

Dwivedi

et al. 2019

Intl Journal of Climatology

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“…BLJs have maximum wind speeds in the BL and are usually explained by the inertial oscillation of ageostrophic winds (Blackadar, 1957) or baroclinicity associated with the terrain (Holton, 1967) or a combination of the two (Du & Rotunno, 2014; Du et al, 2014; Shapiro et al, 2016). The SLLJs have been observed over many regions of the world (e.g., Matsumoto et al, 1971; Squitieri & Gallus, 2016; Xavier et al, 2018; Xue et al, 2018). Numerous studies documented that the SLLJ is one of the important factors contributing to heavy rainfall production over south China and its vicinity (Chen & Yu, 1988; Du & Chen, 2018; Tao & Chen, 1987), through transporting warm, moist air from the tropical oceans, destabilizing the environment, and providing convergence at the terminus of the SLLJ (Chen et al, 1994; Tao & Chen, 1987).…”

Section: Introductionmentioning

confidence: 99%

Roles of Double Low‐Level Jets in the Generation of Coexisting Inland and Coastal Heavy Rainfall Over South China During the Presummer Rainy Season

et al. 2020

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In this study, the key dynamic factors influencing the formation of six heavy-rainfall events with coexisting inland and coastal rainfall over south China during May-June 2011-2017 are investigated using global ensemble forecasts from the European Centre for Medium-Range Weather Forecasts. An ensemble sensitivity analysis and comparisons between the identified good and bad members are conducted. Results confirm the importance of the synoptic low-level jet (SLLJ) and boundary layer jet (BLJ), but with different contributions, in determining the generation of the inland and coastal rainbelts, respectively. The inland heavy rainfall is closely related to both the SLLJ and BLJ, especially their meridional wind components. The more intense cold or quasi-stationary front, low-level vortex, or shear line accompanied by the stronger geostrophic southerly winds within both jets over inland and coastal south China is, the more rainfall over the inland region is favored. The ageostrophic southerly winds of the BLJ make limited contributions to the inland rainfall production but exert greater impacts on the generation of extreme (yet localized) coastal rainfall. The geostrophic meridional winds and associated low-level front/vortex also play a nonnegligible but indispensable role in producing the coastal rainfall. These findings add to our knowledge of heavy rainfall in the East Asian monsoon region.

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“…Except large-scale circulation like prevailing westerlies, the coastal regions are featured with complex small-scale circulations. For instance, the low-level jet (zonal winds with high speed) contributes to rainfall in coastal regions in Asia (Xavier et al, 2018). The orographic effects enhance the precipitation over coastal mountain regions such as the west coast of NA and EU, and the southeast coast of RU (James and Houze, 2005).…”

Section: Own Region and Foreign Contributions To Depositionmentioning

confidence: 99%

“…The mass of aerosols arriving at the coasts of North American (NA) is comparable to that emitted domestically (Yu et al, 2012). Air pollution from Asia contributes to the PM 2.5 concentration in the western US by 1.5 µg m −3 (Tao et al, 2016), the O 3 concentration by 3-10 ppbv (Zhang et al, 2009(Zhang et al, , 2008Yienger et al, 2000;Reidmiller et al, 2009;Jacob et al, 1999;Brown-Steiner and Hess, 2011) and the peroxyacyl nitrate (PAN) concentration by 26 ppbv (Berntsen et al, 1999) in spring. The long-range transport of air pollution from NA is estimated to contribute 3-5 ppb (7 %-11 %) to the O 3 concentration in the EU annually (Auvray and Bey, 2005;Guerova et al, 2006;Derwent et al, 2004;Li et al, 2002) and the increment can reach 25-28 ppbv during particular events (Guerova et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

Source contributions to sulfur and nitrogen deposition – an HTAP II multi-model study on hemispheric transport

Tan

Dentener

et al. 2018

Atmos. Chem. Phys.

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Abstract. With the rising anthropogenic emissions from human activities, elevated concentrations of air pollutants have been detected in the hemispheric air flows in recent years, aggravating the regional air pollution and deposition issues. However, the regional contributions of hemispheric air flows to deposition have been given little attention in the literature. In this light, we assess the impact of hemispheric transport on sulfur (S) and nitrogen (N) deposition for six world regions: North America (NA), Europe (EU), South Asia (SA), East Asia (EA), Middle East (ME) and Russia (RU) in 2010, by using the multi-model ensemble results from the 2nd phase of the Task Force Hemispheric Transport of Air Pollution (HTAP II) with 20 % emission perturbation experiments. About 27 %–58 %, 26 %–46 % and 12 %–23 % of local S, NOx and NH3 emissions and oxidation products are transported and removed by deposition outside of the source regions annually, with seasonal variation of 5 % more in winter and 5 % less in summer. The 20 % emission reduction in the source regions could affect 1 %–10 % of deposition in foreign continental regions and 1 %–14 % in foreign coastal regions and the open ocean. Significant influences are found from NA to the North Atlantic Ocean (2 %–14 %), and from EA to the North Pacific Ocean (4 %–10 %) and to western NA (4 %–6 %) (20 % emission reduction). The impact on deposition caused by short-distance transport between neighboring regions (i.e., from EU to RU) occurs throughout the whole year (slightly stronger in winter), while the long-range transport (i.e., from EA to NA) mainly takes place in spring and fall, which is consistent with the seasonality found for hemispheric transport of air pollutants. Deposition in the emission-intensive regions such as US, SA and EA is dominated (∼80 %) by own-region emissions, while deposition in the low-emission-intensity regions such as RU is almost equally affected by foreign exported emissions (40 %–60 %) and own-region emissions. We also find that deposition of the coastal regions or the near-coastal open ocean is twice more sensitive to hemispheric transport than the non-coastal continental regions, especially for regions in the downwind direction of emission sources (i.e., west coast of NA). This study highlights the significant impacts of hemispheric transport of air pollution on the deposition in coastal regions, the open ocean and low-emission-intensity regions. Further research is proposed to improve the ecosystem and human health, with regards to the enhanced hemispheric air flows.

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The role of monsoon low‐level jet in modulating heavy rainfall events

Cited by 34 publications

References 29 publications

Variability of monsoon low‐level jet and associated rainfall over India

Variability of monsoon low‐level jet and associated rainfall over India

Roles of Double Low‐Level Jets in the Generation of Coexisting Inland and Coastal Heavy Rainfall Over South China During the Presummer Rainy Season

Source contributions to sulfur and nitrogen deposition – an HTAP II multi-model study on hemispheric transport

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