Weakening of North Indian SST Gradients and the Monsoon Rainfall in India and the Sahel

2006 ◽  
Vol 19 (10) ◽  
pp. 2036-2045 ◽  
Author(s):  
Chul Eddy Chung ◽  
V. Ramanathan
Keyword(s):  
Indian Ocean ◽  
South Asian ◽  
Radiative Forcing ◽  
Climate Model ◽  
Monsoon Rainfall ◽  
Equatorial Indian Ocean ◽  
Sub Saharan Africa ◽  
Monsoon Circulation ◽  
Sub Saharan ◽  
Sst Gradient

Abstract Sea surface temperatures (SSTs) in the equatorial Indian Ocean have warmed by about 0.6–0.8 K since the 1950s, accompanied by very little warming or even a slight cooling trend over the northern Indian Ocean (NIO). It is reported that this differential trend has resulted in a substantial weakening of the meridional SST gradient from the equatorial region to the South Asian coast during summer, to the extent that the gradient has nearly vanished recently. Based on simulations with the Community Climate Model Version 3 (CCM3), it is shown that the summertime weakening in the SST gradient weakens the monsoon circulation, resulting in less monsoon rainfall over India and excess rainfall in sub-Saharan Africa. The observed trend in SST is decomposed into a hypothetical uniform warming and a reduction in the meridional gradient. The uniform warming of the tropical Indian Ocean in the authors’ simulations increases the Indian summer monsoon rainfall by 1–2 mm day−1, which is opposed by a larger drying tendency due to the weakening of the SST gradient. The net effect is to decrease the Indian monsoon rainfall, while preventing the sub-Saharan region from becoming too dry. Published coupled ocean–atmosphere model simulations are used to describe the competing effects of the anthropogenic radiative forcing due to greenhouse gases and the anthropogenic South Asian aerosols on the observed SST gradient and the monsoon rainfall.

scholarly journals Africa and the wider world: creole communities in the Atlantic and Indian Oceans

Tempo ◽  
2017 ◽  
Vol 23 (3) ◽  
pp. 465-481
Author(s):  
Malyn Newitt
Keyword(s):  
Technology Transfer ◽  
Indian Ocean ◽  
World Economy ◽  
Sub Saharan Africa ◽  
Eastern Africa ◽  
Cultural Appropriation ◽  
The World ◽  
African Slaves ◽  
The Indian Ocean ◽  
Sub Saharan

Abstract: Portuguese creoles were instrumental in bringing sub-Saharan Africa into the intercontinental systems of the Atlantic and Indian Ocean. In the Atlantic Islands a distinctive creole culture emerged, made up of Christian emigrants from Portugal, Jewish exiles and African slaves. These creole polities offered a base for coastal traders and became politically influential in Africa - in Angola creating their own mainland state. Connecting the African interior with the world economy was largely on African terms and the lack of technology transfer meant that the economic gap between Africa and the rest of the world inexorably widened. African slaves in Latin America adapted to a society already creolised, often through adroit forms of cultural appropriation and synthesis. In eastern Africa Portuguese worked within existing creolised Islamic networks but the passage of their Indiamen through the Atlantic created close links between the Indian Ocean and Atlantic commercial systems.

scholarly journals Systematic Errors in South Asian Monsoon Simulation: Importance of Equatorial Indian Ocean Processes

2017 ◽  
Vol 30 (20) ◽  
pp. 8159-8178 ◽  
Author(s):  
H. Annamalai ◽  
Bunmei Taguchi ◽  
Julian P. McCreary ◽  
Motoki Nagura ◽  
Toru Miyama
Keyword(s):  
Indian Ocean ◽  
South Asia ◽  
South Asian ◽  
Coupled Model ◽  
Equatorial Indian Ocean ◽  
Coupled Processes ◽  
Cmip5 Models ◽  
Model Errors ◽  
Bjerknes Feedback ◽  
Sst Bias

Abstract Forecasting monsoon rainfall using dynamical climate models has met with little success, partly due to models’ inability to represent the monsoon climatological state accurately. In this article the nature and dynamical causes of their biases are investigated. The approach is to analyze errors in multimodel-mean climatological fields determined from CMIP5, and to carry out sensitivity experiments using a coupled model [the Coupled Model for the Earth Simulator (CFES)] that does represent the monsoon realistically. Precipitation errors in the CMIP5 models persist throughout the annual cycle, with positive (negative) errors occurring over the near-equatorial western Indian Ocean (South Asia). Model errors indicate that an easterly wind stress bias Δτ along the equator begins during April–May and peaks during November; the severity of the Δτ is that the Wyrtki jets, eastward-flowing equatorial currents during the intermonsoon seasons (April–May and October–November), are almost eliminated. An erroneous east–west SST gradient (warm west and cold east) develops in June. The structure of the model errors indicates that they arise from Bjerknes feedback in the equatorial Indian Ocean (EIO). Vertically integrated moisture and moist static energy budgets confirm that warm SST bias in the western EIO anchors moist processes that cause the positive precipitation bias there. In CFES sensitivity experiments in which Δτ or warm SST bias over the western EIO is artificially introduced, errors in the EIO are similar to those in the CMIP5 models; moreover, precipitation over South Asia is reduced. An overall implication of these results is that South Asian rainfall errors in CMIP5 models are linked to errors of coupled processes in the western EIO, and in coupled models correct representation of EIO coupled processes (Bjerknes feedback) is a necessary condition for realistic monsoon simulation.

scholarly journals Mixing state of refractory black carbon aerosol in the South Asian outflow over the northern Indian Ocean during winter

2020 ◽  
Author(s):  
Sobhan Kumar Kompalli ◽  
Surendran Nair Suresh Babu ◽  
Krishnaswamy Krishnamoorthy ◽  
Sreedharan Krishnakumari Satheesh ◽  
Mukunda M. Gogoi ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Black Carbon ◽  
South Asian ◽  
Arabian Sea ◽  
Equatorial Indian Ocean ◽  
Mixing State ◽  
Air Masses ◽  
Continental Outflow ◽  
Mass Concentrations

Abstract. Regional climatic implications of aerosol black carbon (BC) are well recognized over South Asia, which has a wide variety of anthropogenic sources in a large abundance. Significant uncertainties remain in its quantification due to lack of sufficient information on the microphysical properties (its concentration, size, and mixing state with other aerosol components), which determine the absorption potential of BC. Especially the information on mixing state of BC is extremely sparse over this region. In this study, first-ever observations of the size distribution and mixing state of individual refractory black carbon (rBC) particles in the south Asian outflow to Southeastern Arabian Sea, northern and equatorial Indian Ocean regions are presented based on measurements using a single particle soot photometer (SP2) aboard the ship cruise of the Integrated Campaign for Aerosols, gases, and Radiation Budget (ICARB-2018) during winter-2018 (16 January to 13 February). The results revealed significant spatial heterogeneity of BC characteristics. Highest rBC mass concentrations (~ 938 ± 293 ng m−3) with the highest relative coating thickness (RCT; the ratio of BC core to its coating diameters) of ~ 2.16 ± 0.19 are found over the Southeast Arabian Sea (SEAS) region, which is in the proximity of the continental outflow. As we move to farther oceanic regions, though the mass concentrations decreased by nearly half (~ 546 ± 80 ng m−3), BC still remained thickly coated (RCT ~ 2.05 ± 0.07). The air over the remote equatorial Indian Ocean, which received considerable marine air masses compared to the other regions, showed the lowest rBC mass concentrations (~ 206 ± 114 ng m−3), with a moderately thick coating (RCT ~ 1.73 ± 0.16). Even over oceanic regions far from the landmass, regions which received the outflow from more industrialized east coast/the Bay of Bengal had thicker coating (~ 104 nm) compared to regions that received outflow from the west coast/peninsular India (~ 86 nm). Although different regions of the ocean depicted contrasting concentrations and mixing state parameters due to varying extent and nature of the continental outflow as well as the atmospheric lifetime of air masses, the modal parameters of rBC mass-size distributions were similar over all the regions. The observed mono-modal distribution with mean mass median diameters (MMD) in the range of 0.19–0.20 μm suggested mixed sources of BC. The mean fraction of BC containing particles (FBC) varied in the range 0.20–0.28 (suggesting significant amounts of non-BC particles), whereas the bulk mixing ratio of coating mass to rBC mass was highest (8.77 ± 2.77) over the outflow regions compared to the remote ocean (4.29 ± 1.54) highlighting the role of outflow in providing condensable material for coating on rBC. These parameters, along with the information on size-resolved mixing state of BC cores, throw light on the role of sources and secondary processing of their complex mixtures for coating on BC under highly polluted conditions. Examination of the non-refractory sub-micrometre aerosol chemical composition obtained using the aerosol chemical speciation monitor (ACSM) suggested that the overall aerosol system was sulfate dominated over the far-oceanic regions. In contrast, organics were equally prominent adjacent to the coastal landmass. Association between the BC mixing state and aerosol chemical composition suggested that sulfate was the probable dominant coating material on rBC cores.

scholarly journals How Does the Tibetan Plateau Affect the Transition of Indian Monsoon Rainfall?

2007 ◽  
Vol 135 (5) ◽  
pp. 2006-2015 ◽  
Author(s):  
Tomonori Sato ◽  
Fujio Kimura
Keyword(s):  
South Asian ◽  
Summer Monsoon ◽  
Climate Model ◽  
Monsoon Rainfall ◽  
Regional Climate ◽  
Reanalysis Data ◽  
North India ◽  
The Tibetan Plateau ◽  
The South ◽  
Northern India

Abstract The roles of the Tibetan Plateau (TP) upon the transition of precipitation in the south Asian summer monsoon are investigated using a simplified regional climate model. Before the onset of the south Asian monsoon, descending flow in the midtroposphere, which can be considered as a suppressor against precipitation, prevails over northern India as revealed by the NCEP–NCAR reanalysis data. The descending motion gradually weakens and retreats from this region before July, consistent with the northwestward migration of the monsoon rainfall. To examine a hypothesis that the dynamical and thermal effects of TP cause the midtropospheric subsidence and its seasonal variation, a series of numerical experiments are conducted using a simplified regional climate model. The mechanical effect of the TP generates robust descending flow over northern India during winter and spring when the zonal westerly flow is relatively strong, but the effect becomes weaker after April as the westerly flow tends to be weaker. The thermal effect of the TP, contrastingly, enhances the descending flow over north India in the premonsoonal season. The descending flow enhanced by the thermal effect of the TP has a seasonal cycle because the global-scale upper-level westerly changes the energy propagation of the thermal forcing response. The subsidence formed by the mechanical and thermal effects of the TP disappears over northern India after the subtropical westerly shifts north of the plateau, the seasonal change of which is in good agreement with that in the reanalysis data. The retreat of the descending flow can be regarded as the withdrawal of the premonsoon season and the commencement of the south Asian monsoon. After that, the deep convection, indicating the onset of the Indian summer monsoon, is able to develop over north India in relation to the ocean–atmosphere and land–atmosphere interaction processes. Northwest India is known to be the latest region of summer monsoon onset in south Asia. Thus, the thermal and mechanical forcing of the TP has great impact on the transition of the Indian monsoon rainfall by changing the midtropospheric circulation.

scholarly journals Response of the South Asian Summer Monsoon to Global Warming: Mean and Synoptic Systems*

2009 ◽  
Vol 22 (4) ◽  
pp. 1014-1036 ◽  
Author(s):  
Markus Stowasser ◽  
H. Annamalai ◽  
Jan Hafner
Keyword(s):  
Indian Ocean ◽  
Arabian Sea ◽  
Climate Model ◽  
Asian Summer Monsoon ◽  
Equatorial Indian Ocean ◽  
South Asian Summer Monsoon ◽  
Eastern Equatorial Indian Ocean ◽  
Asian Summer ◽  
The Mean ◽  
Gfdl Model

Abstract Recent diagnostics with the Geophysical Fluid Dynamics Laboratory Climate Model, version 2.1 (GFDL CM2.1), coupled model’s twentieth-century simulations reveal that this particular model demonstrates skill in capturing the mean and variability associated with the South Asian summer monsoon precipitation. Motivated by this, the authors examine the future projections of the mean monsoon and synoptic systems in this model’s simulations in which quadrupling of CO2 concentrations are imposed. In a warmer climate, despite a weakened cross-equatorial flow, the time-mean precipitation over peninsular parts of India increases by about 10%–15%. This paradox is interpreted as follows: the increased precipitation over the equatorial western Pacific forces an anomalous descending circulation over the eastern equatorial Indian Ocean, the two regions being connected by an overturning mass circulation. The spatially well-organized anomalous precipitation over the eastern equatorial Indian Ocean forces twin anticyclones as a Rossby wave response in the lower troposphere. The southern component of the anticyclone opposes and weakens the climatological cross-equatorial monsoon flow. The patch of easterly anomalies centered in the southern Arabian Sea is expected to deepen the thermocline north of the equator. Both these factors limit the coastal upwelling along Somalia, resulting in local sea surface warming and eventually leading to a local maximum in evaporation over the southern Arabian Sea. It is shown that changes in SST are predominantly responsible for the increase in evaporation over the southern Arabian Sea. The diagnostics suggest that in addition to the increased CO2-induced rise in temperature, evaporation, and atmospheric moisture, local circulation changes in the monsoon region further increase SST, evaporation, and atmospheric moisture, leading to increased rainfall over peninsular parts of India. This result implies that accurate observation of SST and surface fluxes over the Indian Ocean is of urgent need to understand and monitor the response of the monsoon in a warming climate. To understand the regional features of the rainfall changes, the International Pacific Research Center (IPRC) Regional Climate Model (RegCM), with three different resolution settings (0.5° × 0.5°, 0.75° × 0.75°, and 1.0° × 1.0°), was integrated for 20 yr, with lateral and lower boundary conditions taken from the GFDL model. The RegCM solutions confirm the major results obtained from the GFDL model but also capture the orographic nature of monsoon precipitation and regional circulation changes more realistically. The hypothesis that in a warmer climate, an increase in troposphere moisture content favors more intense monsoon depressions is tested. The GFDL model does not reveal any changes, but solutions from the RegCM suggest a statistically significant increase in the number of storms that have wind speeds of 15–20 m s−1 or greater, depending on the resolution employed. Based on these regional model solutions a possible implication is that in a CO2-richer climate an increase in the number of flood days over central India can be expected. The model results obtained here, though plausible, need to be taken with caution since even in this “best” model systematic errors still exist in simulating some aspects of the tropical and monsoon climates.

Identification of the Diadegma species (Hymenoptera: Ichneumonidae, Campopleginae) attacking the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

2000 ◽  
Vol 90 (5) ◽  
pp. 375-389 ◽  
Author(s):  
A.A. Azidah ◽  
M.G. Fitton ◽  
D.L.J. Quicke
Keyword(s):  
New Zealand ◽  
Indian Ocean ◽  
Principal Components ◽  
Plutella Xylostella ◽  
Diamondback Moth ◽  
Identification Key ◽  
Sub Saharan Africa ◽  
Morphometric Study ◽  
Discriminant Analyses ◽  
Sub Saharan

AbstractThe species of Diadegma that attack Plutella xylostella(Linnaeus) are revised. Following a morphometric study involving principal components and discriminant analyses, seven distinct morphospecies are recognized. One species is described as new: D. novaezealandiae from New Zealand. Diadegma mollipla(Holmgren) is the name for the species from sub-Saharan Africa and some Indian Ocean and South Atlantic islands. Diadegma varuna Gupta syn. nov. and D. niponicaKusigemati syn. nov. are both synonymized with D. fenestrale(Holmgren). Diadegma xylostellae Kusigemati is strongly presumed to be a synonym of D. semiclausum (Hellén). An illustrated identification key is provided and each species is described in a standard way.

scholarly journals RCP 8.5 Ghana. High-end climate change impacts on crop production

2020 ◽  
Author(s):  
Sylvia Tramberend ◽  
Günther Fischer ◽  
Harrij van Velthuizen
Keyword(s):  
Climate Change ◽  
High Resolution ◽  
Crop Production ◽  
Agricultural Sector ◽  
Climate Model ◽  
Regional Climate ◽  
Climate Change Impacts ◽  
Development Planning ◽  
Sub Saharan Africa ◽  
Sub Saharan

<p>Climate change threatens vulnerable communities in sub-Saharan Africa who face significant challenges for adaptation. Agriculture provides the livelihood for the majority of population. High-resolution assessments of the effects of climate change on crop production are urgently needed for targeted adaptation planning. In Ghana, next to food needs, agriculture plays an important role on international cocoa markets. To this end, we develop and apply a National Agro-Ecological Zoning system (NAEZ Ghana) to analyze the impacts of high-end (RCP8.5) global warming on agricultural production potentials until the end of this century. NAEZ Ghana uses an ensemble of the CORDEX Africa Regional Climate Model, a regional soil map, to assess development trends of crop production potentials for 19 main crops. Results highlight differential impacts across the country. Especially due to the significant increase in the number of days exceeding high-temperature thresholds, rain-fed production of several food and export crops could be reduced significantly compared to the historical 30-year average (1981-2010). Plantain production, an important food crop, could achieve under climate change less than half of its current potential already in the 2050s and less than 10% by the 2080s. Suitable areas for cocoa production decrease strongly resulting in only one third of production potential compared to today. Other crops with detrimental effects of climate change include oil palm, sugarcane, coffee, and rubber. Production of maize, sorghum, and millet cope well with a future warmer climate. The NAEZ Ghana database provides valuable high-resolution information to support agricultural sector development planning and climate change adaptation strategies. The expansion of irrigation development will play a central role in some areas. This requires further research on Ghana’s linkages between food, water, and energy, taking into account climate and socio-economic changes.</p>

scholarly journals Semiannual Cycle in Zonal Wind over the Equatorial Indian Ocean

2011 ◽  
Vol 24 (24) ◽  
pp. 6471-6485 ◽  
Author(s):  
Tomomichi Ogata ◽  
Shang-Ping Xie
Keyword(s):  
Indian Ocean ◽  
Zonal Wind ◽  
Equatorial Indian Ocean ◽  
Surface Friction ◽  
Ocean Model ◽  
Large Momentum ◽  
Monsoon Circulation ◽  
Budget Analysis ◽  
Basin Mode ◽  
Wind Cycle

Abstract The semiannual cycle in zonal wind over the equatorial Indian Ocean is investigated by use of ocean–atmospheric reanalyses, and linear ocean–atmospheric models. In observations, the semiannual cycle in zonal wind is dominant on the equator and confined in the planetary boundary layer (PBL). Results from a momentum budget analysis show that momentum advection generated by the cross-equatorial monsoon circulation is important for the semiannual zonal-wind cycle in the equatorial Indian Ocean. In experiments with a linearized primitive model of the atmosphere, semiannual momentum forcing due to the meridional advection over the central equatorial Indian Ocean is important to simulate the observed maxima of the semiannual cycle in equatorial zonal wind. Off Somalia, diabatic heating and surface friction over land weaken the semiannual response to large momentum forcing there. Results from a linear ocean model suggest that the semiannual zonal wind stress over the central equatorial Indian Ocean generates large semiannual variability in zonal current through a basin-mode resonance.

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