Investigation of negative cloud radiative forcing over the Indian subcontinent and adjacent oceans during the summer monsoon season

Abstract. Radiative properties of clouds over the Indian subcontinent and nearby oceanic regions (0–25° N, 60–100° E) during the Asian summer monsoon season (June–September) are investigated using the Clouds and Earth's Radiant Energy System (CERES) top-of-the-atmosphere (TOA) flux data. Using multiyear satellite data, the net cloud radiative forcing (NETCRF) at the TOA over the Indian region during the Asian monsoon season is examined. The seasonal mean NETCRF is found to be negative (with its magnitude exceeding ~30 Wm−2) over (1) the northern Bay of Bengal (close to the Myanmar–Thailand coast), (2) the Western Ghats and (3) the coastal regions of Myanmar. Such strong negative NETCRF values observed over the Indian monsoon region contradict the assumption that near cancellation between LWCRF and SWCRF is a generic property of all tropical convective regions. The seasonal mean cloud amount (high and upper middle) and corresponding cloud optical depth observed over the three regions show relatively large values compared to the rest of the Indian monsoon region. Using satellite-derived cloud data, a statistical cloud vertical model delineating the cloud cover and single-scattering albedo was developed for the three negative NETCRF regions. The shortwave (SW), longwave (LW) and net cloud radiative forcing over the three negative NETCRF regions are calculated using the rapid radiative transfer model (RRTM) with the cloud vertical model as input. The NETCRF estimated from CERES observations show good comparison with that computed using RRTM (within the uncertainty limit of CERES observations). Sensitivity tests are conducted using RRTM to identify the parameters that control the negative NETCRF observed over these regions during the summer monsoon season. Increase in atmospheric water vapor content during the summer monsoon season is found to influence the negative NETCRF values observed over the region.

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Investigation of negative cloud radiative forcing over the Indian subcontinent and adjacent oceans during the summer monsoon season

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-28895-2013 ◽

2013 ◽

Vol 13 (11) ◽

pp. 28895-28951

Author(s):

B. V. Thampi ◽

R. Roca

Keyword(s):

Summer Monsoon ◽

Radiative Forcing ◽

Indian Monsoon ◽

Indian Subcontinent ◽

Monsoon Season ◽

Radiative Properties ◽

Monsoon Region ◽

Summer Monsoon Season ◽

Cloud Radiative Forcing ◽

Indian Monsoon Region

Abstract. Radiative properties of clouds over the Indian subcontinent and nearby oceanic regions (0–25° N, 60–100° E) during the Asian summer monsoon season (June–September) are investigated using the Clouds and Earth's Radiant Energy System (CERES) Top of the Atmosphere (TOA) flux data. Using multi-year satellite data, the net cloud radiative forcing (NETCRF) at the TOA over the Indian region during the Asian monsoon season is examined. The seasonal mean NETCRF is found to be negative (with its magnitude exceeding ~ 30 W m−2) over (1) the northern Bay of Bengal (close to the Myanmar–Thailand coast), (2) the Western Ghats and (3) the coastal regions of Myanmar. Such strong negative NETCRF values observed over the Indian monsoon region contradicts the assumption that near cancellation between LWCRF and SWCRF is a generic property of all tropical convective regions. The seasonal mean cloud amount (high and upper middle) and corresponding cloud optical depth observed over the three regions show relatively large values compared to rest of the Indian monsoon region. Using satellite derived cloud data, a statistical cloud vertical model delineating the cloud cover and single scattering albedo was developed for the three negative NETCRF regions. The shortwave (SW), longwave (LW) and net cloud radiative forcing over the three negative NETCRF regions are calculated using the Rapid Radiative Transfer Model (RRTM) with cloud vertical model as input. The NETCRF estimated from CERES observations show good comparison with that computed using RRTM (within the uncertainty limit of CERES observations). Sensitivity tests are conducted using RRTM to identify the parameters that control the negative NETCRF observed over these regions during the summer monsoon season. Increase in atmospheric water vapor content during the summer monsoon season is found to influence the negative NETCRF values observed over the region.

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A satellite-based 13-year climatology of net cloud radiative forcing over the Indian monsoon region

Atmospheric Research ◽

10.1016/j.atmosres.2016.07.017 ◽

2016 ◽

Vol 182 ◽

pp. 76-86 ◽

Cited By ~ 14

Author(s):

Trailokya Saud ◽

Sagnik Dey ◽

Sushant Das ◽

Soumi Dutta

Keyword(s):

Radiative Forcing ◽

Indian Monsoon ◽

Monsoon Region ◽

Cloud Radiative Forcing ◽

Indian Monsoon Region

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The cloud radiative forcing over Asian-Pacific summer monsoon region

Terrestrial Atmospheric and Oceanic Sciences ◽

10.3319/tao.2003.14.4.445(a) ◽

2003 ◽

Vol 14 (4) ◽

pp. 445 ◽

Cited By ~ 1

Author(s):

Wen-Shung Kau ◽

Chi-Hua Wu ◽

Chih-Hua Tsou

Keyword(s):

Summer Monsoon ◽

Radiative Forcing ◽

Monsoon Region ◽

Cloud Radiative Forcing ◽

Asian Pacific ◽

Summer Monsoon Region

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Snow-darkening versus direct radiative effects of mineral dust aerosol on the Indian summer monsoon onset: role of temperature change over dust sources

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-1605-2019 ◽

2019 ◽

Vol 19 (3) ◽

pp. 1605-1622 ◽

Cited By ~ 11

Author(s):

Zhengguo Shi ◽

Xiaoning Xie ◽

Xinzhou Li ◽

Liu Yang ◽

Xiaoxun Xie ◽

...

Keyword(s):

Tibetan Plateau ◽

Central Asia ◽

Black Carbon ◽

Summer Monsoon ◽

Indian Summer Monsoon ◽

Radiative Forcing ◽

Indian Monsoon ◽

Indian Subcontinent ◽

Direct Radiative Forcing

Abstract. Atmospheric absorptive aerosols exert complicated effects on the climate system, two of which are through their direct radiative forcing and snow-darkening forcing. Compared to black carbon, the snow-darkening effect of dust on climate has been scarcely explored till now. When depositing in snow, dust can reduce the albedo of snow by darkening it and increasing the snowmelt. In this study, the snow-darkening effect of dust, as well as the direct radiative effect, on the Indian summer monsoon are evaluated by atmospheric general circulation model experiments. The results show that the snow-darkening and direct radiative forcing of dust both have significant impacts on the onset of the Indian monsoon, but they are distinctly opposite. The snow-darkening effect of dust weakens the Indian monsoon precipitation during May and June, opposite to black carbon. The surface temperature over central Asia and the western Tibetan Plateau becomes warmer due to the dust-induced decrease in snow cover, which leads to a local low-level cyclonic anomaly as well as an anticyclonic anomaly over the Indian subcontinent and Arabian Sea. This circulation pattern allows air currents penetrating into the Indian subcontinent more from central Asia but less from the Indian Ocean. In contrast, the direct radiative forcing of dust warms the low troposphere over the Arabian Peninsula, which intensifies moisture convergence and precipitation over the Indian monsoon region. The upper tropospheric atmospheric circulation over Asia is also sensitive to both effects. Compared to previous studies which emphasized the temperature over the Tibetan Plateau, our results further highlight an important role of surface/low tropospheric temperature changes over dust source areas, which can also significantly modify the response of summer monsoon. Thus, links between the climatic impact of dust and complicated thermal conditions over Asia are of importance and need to be clarified accurately.

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Representation of Rossby wave propagation and its effect on the teleconnection between the Indian summer monsoon and extratropical rainfall in the Met Office Unified Model

10.21203/rs.3.rs-255748/v1 ◽

2021 ◽

Author(s):

Xinxin Tang ◽

Jianping Li ◽

Huqiang Zhang ◽

Sen Zhao

Keyword(s):

South Asian ◽

Summer Monsoon ◽

Rossby Wave ◽

Indian Summer Monsoon ◽

Monsoon Rainfall ◽

Indian Monsoon ◽

Unified Model ◽

Monsoon Region ◽

Indian Monsoon Region ◽

Dry Bias

Abstract Compared with Global Atmosphere 6 (GA6) of the UK Met Office Unified Model (UM), the dry bias over the Indian monsoon region in Global Atmosphere 7 (GA7) is significantly reduced. However, the physical processes controlling how this reduced dry bias in India influences rainfall teleconnections in the extratropics remain unclear. Thus, in this study, we use Rossby wave tracing in a horizontally nonuniform background flow to investigate how the improved simulation of monsoon rainfall in GA7 compared with GA6 affects extratropical rainfall teleconnections. We find that wave rays emanating from the upper troposphere in the Indian monsoon region first propagate westward, then divide into the Northern Hemisphere (NH) subtropical westerlies over Asia and the Southern Hemisphere (SH) subtropical westerlies. The wave ray trajectories in GA7 in years of strong Indian summer monsoon rainfall (ISMR) are closer to observations than those in GA6. We also find that the upper tropospheric meridional winds over the South Asian monsoon region and western Tibetan Plateau are much better simulated in GA7 than in GA6 owning to the improvement of ISMR and South Asian High (SAH), which leads to a more realistic simulation of the wave rays in GA7. The better simulated circulation teleconnections in GA7 then modulate the vertical motion and moisture transport, and hence affect extratropical rainfall anomalies in the NH and SH. This paper provides new insights for the assessment of tropical–extratropical teleconnections in models.

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IMDAA: High Resolution Satellite-era Reanalysis for the Indian Monsoon Region

Journal of Climate ◽

10.1175/jcli-d-20-0412.1 ◽

2021 ◽

pp. 1-78

Author(s):

S. Indira Rani ◽

Arulalan T ◽

John P. George ◽

E. N. Rajagopal ◽

Richard Renshaw ◽

...

Keyword(s):

High Resolution ◽

Data Assimilation ◽

Summer Monsoon ◽

Land Surface ◽

Indian Monsoon ◽

India Meteorological Department ◽

Summer Monsoon Rainfall ◽

Monsoon Region ◽

Fine Grid ◽

Indian Monsoon Region

AbstractA high resolution regional reanalysis of the Indian Monsoon Data Assimilation and Analysis (IMDAA) project is made available to researchers for deeper understanding of the Indian monsoon and its variability. This 12 km resolution reanalysis covering the satellite-era from 1979 to 2018 using 4D-Var data assimilation method and the UK Met Unified Model is presently the highest resolution atmospheric reanalysis carried out for the Indian monsoon region. Conventional and satellite observations from different sources are used, including Indian surface and upper air observations, of which some were not used in any previous reanalyses. Various aspects of this reanalysis, like quality control and bias correction of observations, data assimilation system, land surface analysis, and verification of reanalysis products, are presented in this paper. Representation of important weather phenomena of each season over India in the IMDAA reanalysis verifies reasonably well against India Meteorological Department (IMD) observations and compares closely with ERA5. Salient features of the Indian summer monsoon are found to be well represented in the IMDAA reanalysis. Characteristics of major semi-permanent summer monsoon features (e.g., Low-level Jet and Tropical Easterly Jet) in IMDAA reanalysis are consistent with ERA5. The IMDAA reanalysis has captured the mean, inter-annual, and intra-seasonal variability of summer monsoon rainfall fairly well. IMDAA produces a slightly cooler winter and a hotter summer than the observations; the reverse for ERA5. IMDAA captured the fine-scale features associated with a notable heavy rainfall episode over complex terrain. In this study, the fine grid spacing nature of IMDAA is compromised due to the lack of comparable resolution observations for verification.

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Comparing cloud radiative properties between the Eastern China and the Indian monsoon region

Advances in Atmospheric Sciences ◽

10.1007/s00376-001-0025-1 ◽

2001 ◽

Vol 18 (6) ◽

pp. 1090-1102 ◽

Cited By ~ 39

Author(s):

Yu Rucong ◽

Yu Yongqiang ◽

Zhang Minghua

Keyword(s):

Indian Monsoon ◽

Eastern China ◽

Radiative Properties ◽

Monsoon Region ◽

Indian Monsoon Region ◽

Cloud Radiative Properties

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Intraseasonal Modulation of the Indian Summer Monsoon

10.1093/acrefore/9780190228620.013.616 ◽

2018 ◽

Author(s):

Bin Wang

Keyword(s):

Summer Monsoon ◽

Indian Summer Monsoon ◽

Indian Monsoon ◽

Vertical Shear ◽

Boreal Summer ◽

Convective System ◽

Enhancement Effect ◽

Monsoon Region ◽

Northward Propagation ◽

Indian Monsoon Region

The strongest Indian summer monsoon (ISM) on the planet features prolonged clustered spells of wet and dry conditions often lasting for two to three weeks, known as active and break monsoons. The active and break monsoons are attributed to a quasi-periodic intraseasonal oscillation (ISO), which is an extremely important form of the ISM variability bridging weather and climate variation. The ISO over India is part of the ISO in global tropics. The latter is one of the most important meteorological phenomena discovered during the 20th century (Madden & Julian, 1971, 1972). The extreme dry and wet events are regulated by the boreal summer ISO (BSISO). The BSISO over Indian monsoon region consists of northward propagating 30–60 day and westward propagating 10–20 day modes. The “clustering” of synoptic activity was separately modulated by both the 30–60 day and 10–20 day BSISO modes in approximately equal amounts. The clustering is particularly strong when the enhancement effect from both modes acts in concert. The northward propagation of BSISO is primarily originated from the easterly vertical shear (increasing easterly winds with height) of the monsoon flows, which by interacting with the BSISO convective system can generate boundary layer convergence to the north of the convective system that promotes its northward movement. The BSISO-ocean interaction through wind-evaporation feedback and cloud-radiation feedback can also contribute to the northward propagation of BSISO from the equator. The 10–20 day oscillation is primarily produced by convectively coupled Rossby waves modified by the monsoon mean flows. Using coupled general circulation models (GCMs) for ISO prediction is an important advance in subseasonal forecasts. The major modes of ISO over Indian monsoon region are potentially predictable up to 40–45 days as estimated by multiple GCM ensemble hindcast experiments. The current dynamical models’ prediction skills for the large initial amplitude cases are approximately 20–25 days, but the prediction of developing BSISO disturbance is much more difficult than the prediction of the mature BSISO disturbances. This article provides a synthesis of our current knowledge on the observed spatial and temporal structure of the ISO over India and the important physical processes through which the BSISO regulates the ISM active-break cycles and severe weather events. Our present capability and shortcomings in simulating and predicting the monsoon ISO and outstanding issues are also discussed.

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