scholarly journals Consistent response of Indian summer monsoon to Middle East dust in observations and simulations

2015 ◽  
Vol 15 (11) ◽  
pp. 15571-15619 ◽  
Author(s):  
Q. Jin ◽  
J. Wei ◽  
Z.-L. Yang ◽  
B. Pu ◽  
J. Huang
Keyword(s):  
Boundary Layer ◽  
Middle East ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Arabian Sea ◽  
Dust Emission ◽  
Shortwave Radiation ◽  
Dust Aerosols ◽  
Northern India ◽  
Southwest India

Abstract. The response of the Indian summer monsoon (ISM) circulation and precipitation to Middle East dust aerosols on sub-seasonal timescales is studied using observations and the Weather Research and Forecasting model with chemistry (WRF-Chem). Satellite data shows that the ISM rainfall in coastal southwest India, central and northern India, and Pakistan are closely associated with Middle East dust aerosols. The physical mechanism behind this dust–ISM rainfall connection is examined through ensemble simulations with and without dust emission. Each ensemble includes 16 members with various physical and chemical schemes to consider the model uncertainties in parameterizing shortwave radiation, the planetary boundary layer, and aerosol chemical mixing rules. Experiments show that dust aerosols increase rainfall by about 0.44 mm day−1 (~ 10%) in coastal southwest India, central and northern India, and northern Pakistan, a pattern consistent with the observed relationship. The ensemble mean rainfall response over India shows much stronger spatial correlation with the observed rainfall response than any of the ensemble members. The largest modeling uncertainties are from the boundary layer schemes, followed by shortwave radiation schemes. In WRF-Chem, the dust AOD over the Middle East shows the strongest correlation with the ISM rainfall response when dust AOD leads rainfall response by about 11 days. Further analyses show that the increased ISM rainfall is related to the enhanced southwesterly flow and moisture transport from the Arabian Sea to the Indian subcontinent, which are associated with the development of an anomalous low pressure system over the Arabian Sea, the southern Arabian Peninsula, and the Iranian Plateau due to dust-induced heating in the lower troposphere (800–500 hPa). This study demonstrates a thermodynamic mechanism that links remote desert dust emission in the Middle East to the ISM circulation and precipitation variability on sub-seasonal timescales, which may have implications for ISM rainfall forecasts.

scholarly journals Consistent response of Indian summer monsoon to Middle East dust in observations and simulations

2015 ◽  
Vol 15 (17) ◽  
pp. 9897-9915 ◽  
Author(s):  
Q. Jin ◽  
J. Wei ◽  
Z.-L. Yang ◽  
B. Pu ◽  
J. Huang
Keyword(s):  
Middle East ◽  
Arabian Sea ◽  
Short Wave ◽  
Wave Radiation ◽  
Short Wave Radiation ◽  
Iranian Plateau ◽  
Dust Emissions ◽  
Dust Aerosols ◽  
Northern India ◽  
Southwest India

Abstract. The response of the Indian summer monsoon (ISM) circulation and precipitation to Middle East dust aerosols on sub-seasonal timescales is studied using observations and the Weather Research and Forecasting model coupled with online chemistry (WRF-Chem). Satellite data show that the ISM rainfall in coastal southwest India, central and northern India, and Pakistan is closely associated with the Middle East dust aerosols. The physical mechanism behind this dust–ISM rainfall connection is examined through ensemble simulations with and without dust emissions. Each ensemble includes 16 members with various physical and chemical schemes to consider the model uncertainties in parameterizing short-wave radiation, the planetary boundary layer, and aerosol chemical mixing rules. Experiments show that dust aerosols increase rainfall by about 0.44 mm day−1 (~10 % of the climatology) in coastal southwest India, central and northern India, and north Pakistan, a pattern consistent with the observed relationship. The ensemble mean rainfall response over India shows a much stronger spatial correlation with the observed rainfall response than any other ensemble members. The largest modeling uncertainties are from the boundary layer schemes, followed by short-wave radiation schemes. In WRF-Chem, the dust aerosol optical depth (AOD) over the Middle East shows the strongest correlation with the ISM rainfall response when dust AOD leads rainfall response by about 11 days. Further analyses show that increased ISM rainfall is related to enhanced southwesterly monsoon flow and moisture transport from the Arabian Sea to the Indian subcontinent, which are associated with the development of an anomalous low-pressure system over the Arabian Sea, the southern Arabian Peninsula, and the Iranian Plateau due to dust-induced heating in the troposphere. The dust-induced heating in the mid-upper troposphere is mainly located in the Iranian Plateau rather than the Tibetan Plateau. This study demonstrates a thermodynamic mechanism that links remote desert dust emissions in the Middle East to ISM circulation and precipitation variability on sub-seasonal timescales, which may have implications for ISM rainfall forecasts.

Influence of the Arabian Sea on the Indian summer monsoon

Tellus ◽  
1978 ◽  
Vol 30 (2) ◽  
pp. 117-125 ◽  
Author(s):  
S. K. Ghosh ◽  
M. C. Pant ◽  
B. N. Dewan
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Arabian Sea

scholarly journals On the Detection of Onset and Activity of the Indian Summer Monsoon Using GPS RO Refractivity Profiles

2013 ◽  
Vol 141 (6) ◽  
pp. 2096-2106 ◽  
Author(s):  
V. V. M. Jagannadha Rao ◽  
M. Venkat Ratnam ◽  
Y. Durga Santhi ◽  
M. Roja Raman ◽  
M. Rajeevan ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Arabian Sea ◽  
Active Phase ◽  
Monsoon Onset ◽  
Tropospheric Temperature ◽  
Sudden Increase ◽  
Atmospheric Conditions ◽  
Good Relation ◽  
Onset Phase

Abstract Global positioning system (GPS) radio occultation (RO) data available during 2001–10 have been used to examine the variations in the refractivity during the onset of Indian summer monsoon (ISM) over the east Arabian Sea (5°–15°N, 65°–75°E). An enhancement of 5–10 N-units in the refractivity is observed around 4.8 km (~600 hPa) a few days (9.23 ± 3.6 days) before onset of the monsoon over Kerala, India. This is attributed to moisture buildup over the Arabian Sea during the monsoon onset phase. A sudden increase (1.5–2 K) in mean upper-tropospheric temperature at the time of onset and during the active phase of the monsoon is attributed to convective activity and the release of latent heat. On the day of monsoon onset over Kerala, an appreciable dip in the refractivity is observed that persisted for 1–3 days followed by an enhancement in refractivity with the active phase of the monsoon. An arbitrary value of 128 N-units difference between 4.8 km (~600 hPa) and 16 km (~100 hPa) coupled with a dip in refractivity on the day of monsoon arrival might give an indication of clear transition of atmospheric conditions and the detection of monsoon onset. Further, a good relation is also found between the activity of monsoon and variability in the refractivity.

scholarly journals Irrigation-Induced Land–Atmosphere Feedbacks and Their Impacts on Indian Summer Monsoon

2018 ◽  
Vol 31 (21) ◽  
pp. 8785-8801 ◽  
Author(s):  
Chihchung Chou ◽  
Dongryeol Ryu ◽  
Min-Hui Lo ◽  
Hao-Wei Wey ◽  
Hector M. Malano
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Land Surface ◽  
Large Scale ◽  
Coupled Model ◽  
North India ◽  
Shortwave Radiation ◽  
Surface Cooling ◽  
Limited Region ◽  
Feedback Mechanisms

From the 1980s, Indian summer monsoon rainfall (ISMR) shows a decreasing trend over north and northwest India, and there was a significant observed reduction in July over central and south India in 1982–2003. The key drivers of the changed ISMR, however, remain unclear. It was hypothesized that the large-scale irrigation development that started in the 1950s has resulted in land surface cooling, which slowed large-scale atmospheric circulation, exerting significant influences on ISMR. To test this hypothesis, a fully coupled model, the CESM v1.0.3, was used with a global irrigation dataset. In this study, spatially varying irrigation-induced feedback mechanisms are investigated in detail at different stages of the monsoon. Results show that soil moisture and evapotranspiration increase significantly over India throughout the summertime because of the irrigation. However, 2-m air temperature shows a significant reduction only in a limited region because the temperature change is influenced simultaneously by surface incoming shortwave radiation and evaporative cooling resulting from the irrigation, especially over the heavily irrigated region. Irrigation also induces a 925-hPa northeasterly wind from 30°N toward the equator. This is opposite to the prevailing direction of the Indian summer monsoon (ISM) wind that brings moist air to India. The modeled rainfall in the irrigated case significantly decreases up to 1.5 mm day−1 over central and north India from July to September. This paper reveals that the irrigation can contribute to both increasing and decreasing the surface temperature via multiple feedback mechanisms. The net effect is to weaken the ISM with the high spatial and temporal heterogeneity.

Long-term history of sediment inputs to the eastern Arabian Sea and its implications for the evolution of the Indian summer monsoon since 3.7 Ma

2018 ◽  
Vol 157 (6) ◽  
pp. 908-919 ◽  
Author(s):  
Mingjiang Cai ◽  
Zhaokai Xu ◽  
Peter D. Clift ◽  
Boo-Keun Khim ◽  
Dhongil Lim ◽  
...  
Keyword(s):  
Clay Minerals ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Arabian Sea ◽  
Sediment Supply ◽  
Deccan Traps ◽  
Indus River ◽  
Eastern Arabian Sea ◽  
Monsoon Intensity ◽  
History Of

AbstractWe present a new set of clay mineral and grain-size data for the siliciclastic sediment fraction from International Ocean Discovery Program (IODP) Site U1456 located in the eastern Arabian Sea to reconstruct the variabilities in the continental erosion and weathering intensity in the western Himalaya, elucidate the sediment source-to-sink processes and discuss the potential controls underlying these changes since 3.7 Ma. The clay minerals mainly consist of smectite (0–90%, average 44%) and illite (3–90%, average 44%), with chlorite (1–26%, average 7%) and kaolinite (0–19%, average 5%) as minor components. The compositional variations in the clay minerals at IODP Site U1456 suggest four phases of sediment provenance: the Indus River (phase 1, 3.7–3.2 Ma), the Indus River and Deccan Traps (phase 2, 3.2–2.6 Ma), the Indus River (phase 3, 2.6–1.2 Ma) and the Indus River and Deccan Traps (phase 4, 1.2–0 Ma). These provenance changes since 3.7 Ma can be correlated with variations in the Indian summer monsoon intensity. The siliciclastic sediments in the eastern Arabian Sea were mainly derived from the Indus River when the Indian summer monsoon was generally weak. In contrast, when the Indian summer monsoon intensified, the siliciclastic sediment supply from the Deccan Traps increased. In particular, this study shows that the smectite/(illite+chlorite) ratio is a sensitive tool for reconstructing the history of the variation in the Indian summer monsoon intensity over the continents surrounding the Arabian Sea since 3.7 Ma.

scholarly journals Objective Definition of the Indian Summer Monsoon Onset*

2009 ◽  
Vol 22 (12) ◽  
pp. 3303-3316 ◽  
Author(s):  
Bin Wang ◽  
Qinghua Ding ◽  
P. V. Joseph
Keyword(s):  
Indian Ocean ◽  
Excellent Agreement ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Time Scale ◽  
Rainy Season ◽  
Arabian Sea ◽  
Monsoon Onset ◽  
Indian Peninsula ◽  
The Past

Abstract The onset of the Indian summer monsoon (ISM) over the southern tip of the Indian peninsula [also known as monsoon onset over Kerala (MOK)] has been considered the beginning of India’s rainy season. The Indian Meteorological Department (IMD) makes an official prediction of ISM onset every year using a subjective method. Based on an analysis of the past 60-yr (1948–2007) record, the authors show that the onset date can be objectively determined by the beginning of the sustained 850-hPa zonal wind averaged over the southern Arabian Sea (SAS) from 5° to 15°N, and from 40° to 80°E. The rapid establishment of a steady SAS westerly is in excellent agreement with the abrupt commencement of the rainy season over the southern tip of the Indian peninsula. In 90% of the years analyzed, this simple and objective index has excellent agreement with the onset dates that are subjectively defined by the IMD. There are only 3 yr of the past 60 yr during which the two onset dates differ by more than 10 days, and none of them perfectly reflects the MOK. A prominent onset precursor on the biweekly time scale is the westward extension of the convection center from the equatorial eastern Indian Ocean toward the southeast Arabian Sea. On the intraseasonal time scale, the onset tends to be led by northeastward propagation of an intraseasonal convective anomaly from the western equatorial Indian Ocean. The objective determination of the onset based on the SAS low-level westerly is a characteristic representation of the complex process of the ISM onset. Given its objectiveness and its representation of the large-scale circulation, the proposed new onset definition provides a useful metric for verifying numerical model performance in simulating and predicting the ISM onset and for studying predictability of interannual variations of the onset.

scholarly journals The Role of the Western Arabian Sea Upwelling in Indian Monsoon Rainfall Variability

2008 ◽  
Vol 21 (21) ◽  
pp. 5603-5623 ◽  
Author(s):  
Takeshi Izumo ◽  
Clémentde Boyer Montégut ◽  
Jing-Jia Luo ◽  
Swadhin K. Behera ◽  
Sébastien Masson ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Arabian Sea ◽  
Monsoon Rainfall ◽  
Indian Monsoon ◽  
Indian Summer Monsoon Rainfall ◽  
Summer Monsoon Rainfall ◽  
Indian Monsoon Rainfall ◽  
Precipitation Anomalies

Abstract The Indian summer monsoon rainfall has complex, regionally heterogeneous, interannual variations with huge socioeconomic impacts, but the underlying mechanisms remain uncertain. The upwelling along the Somalia and Oman coasts starts in late spring, peaks during the summer monsoon, and strongly cools the sea surface temperature (SST) in the western Arabian Sea. They restrict the westward extent of the Indian Ocean warm pool, which is the main moisture source for the monsoon rainfall. Thus, variations of the Somalia–Oman upwelling can have significant impacts on the moisture transport toward India. Here the authors use both observations and an advanced coupled atmosphere–ocean general circulation model to show that a decrease in upwelling strengthens monsoon rainfall along the west coast of India by increasing the SST along the Somalia–Oman coasts, and thus local evaporation and water vapor transport toward the Indian Western Ghats (mountains). Further observational analysis reveals that such decreases in upwelling are caused by anomalously weak southwesterly winds in late spring over the Arabian Sea that are due to warm SST/increased precipitation anomalies over the Seychelles–Chagos thermocline ridge of the southwestern Indian Ocean (and vice versa for years with strong upwelling/weak west Indian summer monsoon rainfall). The latter SST/precipitation anomalies are often related to El Niño conditions and the strength of the Indonesian–Australian monsoon during the previous winter. This sheds new light on the ability to forecast the poorly predicted Indian monsoon rainfall on a regional scale, helped by a proper ocean observing/forecasting system in the western tropical Indian Ocean.

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