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Jasti S. Chowdary Anant Parekh Rashmi Kakatkar C. Gnanaseelan G. Srinivas Prem Singh M. K. Roxy 《Climate Dynamics》2016,47(3-4):831-844
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J. S. Chowdary C. Gnanaseelan Soumi Chakravorty 《Theoretical and Applied Climatology》2013,113(1-2):329-336
Influence of northwest (NW) Pacific anticyclone on the Indian summer monsoon (ISM), particularly over the head Bay of Bengal and monsoon trough region, is investigated. Strong NW Pacific anticyclone during summer induces negative precipitation anomalies over the head Bay of Bengal and Gangetic Plain region. Westward extension of moisture divergence and dry moisture transport from NW Pacific associated with anticyclone (ridge) and local Hadley cell-induced subsidence are responsible for these negative precipitation anomalies. The impact is maximum when the anticyclone and Indian Ocean basin warming co-occur. This contributes significantly to year-to-year variability of ISM. 相似文献
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Climate Dynamics - The Tropical Indian Ocean (TIO) is seen to exhibit robust warming after the 1950s. Most of the previous studies on the Indian Ocean (IO) surface and subsurface temperature... 相似文献
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A. Jayakumar J��r?me Vialard M. Lengaigne C. Gnanaseelan Julian P. McCreary B. Praveen Kumar 《Climate Dynamics》2011,37(11-12):2217-2234
During boreal winter, there is a prominent maximum of intraseasonal sea-surface temperature (SST) variability associated with the Madden?CJulian Oscillation (MJO) along a Thermocline Ridge located in the southwestern Indian Ocean (5°S?C10°S, 60°E?C90°E; TRIO region). There is an ongoing debate about the relative importance of air-sea heat fluxes and oceanic processes in driving this intraseasonal SST variability. Furthermore, various studies have suggested that interannual variability of the oceanic structure in the TRIO region could modulate the amplitude of the MJO-driven SST response. In this study, we use observations and ocean general circulation model (OGCM) experiments to quantify these two effects over the 1997?C2006 period. Observational analysis indicates that Ekman pumping does not contribute significantly (on average) to intraseasonal SST variability. It is, however, difficult to quantify the relative contribution of net heat fluxes and entrainment to SST intraseasonal variability from observations alone. We therefore use a suite of OGCM experiments to isolate the impacts of each process. During 1997?C2006, wind stress contributed on average only about 20% of the intraseasonal SST variability (averaged over the TRIO region), while heat fluxes contributed about 70%, with forcing by shortwave radiation (75%) dominating the other flux components (25%). This estimate is consistent with an independent air-sea flux product, which indicates that shortwave radiation contributes 68% of intraseasonal heat flux variability. The time scale of the heat-flux perturbation, in addition to its amplitude, is also important in controlling the intraseasonal SST signature, with longer periods favouring a larger response. There are also strong year-to-year variations in the respective role of heat fluxes and wind stress. Of the five strong cooling events identified in both observations and the model (two in 1999 and one in 2000, 2001 and 2002), intraseasonal-wind stress dominates the SST signature during 2001 and contributes significantly during 2000. Interannual variations of the subsurface thermal structure associated with the Indian Ocean Dipole or El Ni?o/La Ni?a events modulate the MJO-driven SST signature only moderately (by up to 30%), mainly by changing the temperature of water entrained into the mixed layer. The primary factor that controls year-to-year changes in the amplitude of TRIO, intraseasonal SST anomalies is hence the characteristics of intraseasonal surface flux perturbations, rather than changes in the underlying oceanic state. 相似文献
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J. S. Chowdary H. S. Chaudhari C. Gnanaseelan Anant Parekh A. Suryachandra Rao P. Sreenivas S. Pokhrel P. Singh 《Climate Dynamics》2014,42(7-8):1925-1947
This study investigates the El Niño Southern Oscillation (ENSO) teleconnections to tropical Indian Ocean (TIO) and their relationship with the Indian summer monsoon in the coupled general circulation model climate forecast system (CFS). The model shows good skill in simulating the impact of El Niño over the Indian Oceanic rim during its decay phase (the summer following peak phase of El Niño). Summer surface circulation patterns during the developing phase of El Niño are more influenced by local Sea Surface Temperature (SST) anomalies in the model unlike in observations. Eastern TIO cooling similar to that of Indian Ocean Dipole (IOD) is a dominant model feature in summer. This anomalous SST pattern therefore is attributed to the tendency of the model to simulate more frequent IOD events. On the other hand, in the model baroclinic response to the diabatic heating anomalies induced by the El Niño related warm SSTs is weak, resulting in reduced zonal extension of the Rossby wave response. This is mostly due to weak eastern Pacific summer time SST anomalies in the model during the developing phase of El Niño as compared to observations. Both eastern TIO cooling and weak SST warming in El Niño region combined together undermine the ENSO teleconnections to the TIO and south Asia regions. The model is able to capture the spatial patterns of SST, circulation and precipitation well during the decay phase of El Niño over the Indo-western Pacific including the typical spring asymmetric mode and summer basin-wide warming in TIO. The model simulated El Niño decay one or two seasons later, resulting long persistent warm SST and circulation anomalies mainly over the southwest TIO. In response to the late decay of El Niño, Ekman pumping shows two maxima over the southern TIO. In conjunction with this unrealistic Ekman pumping, westward propagating Rossby waves display two peaks, which play key role in the long-persistence of the TIO warming in the model (for more than a season after summer). This study strongly supports the need of simulating the correct onset and decay phases of El Niño/La Niña for capturing the realistic ENSO teleconnections. These results have strong implications for the forecasting of Indian summer monsoon as this model is currently being adopted as an operational model in India. 相似文献
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S. S. C. Shenoi D. Shankar G. S. Michael J. Kurian K. K. Varma M. R. Ramesh Kumar A. M. Almeida A. S. Unnikrishnan W. Fernandes N. Barreto C. Gnanaseelan R. Mathew K. V. Praju V. Mahale 《Journal of Earth System Science》2005,114(5):475-491
This paper describes the hydrographic observations in the southeastern Arabian Sea (SEAS) during two cruises carried out in
March–June 2003 as part of the Arabian Sea Monsoon Experiment. The surface hydrography during March–April was dominated by
the intrusion of low-salinity waters from the south; during May–June, the low-salinity waters were beginning to be replaced
by the highsalinity waters from the north. There was considerable mixing at the bottom of the surface mixed layer, leading
to interleaving of low-salinity and high-salinity layers. The flow paths constructed following the spatial patterns of salinity
along the sections mimic those inferred from numerical models. Time-series measurements showed the presence of Persian Gulf
and Red Sea Waters in the SEAS to be intermittent during both cruises: they appeared and disappeared during both the fortnight-long
time series. 相似文献
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The epochal changes in the seasonal evolution of El Niño induced tropical Indian Ocean (TIO) warming in the context of mid-1970s regime shift is investigated in this study. El Niño induced warming is delayed by one season in the northern TIO during epoch-2 (post mid-1970) and southern TIO during epoch-1 (pre mid-1970). Significant spatiotemporal changes in TIO (especially in the north) warming are apparent during the developing phase of El Niño. The ocean dynamics is the major driver in the basin wide warming during epoch-2 whereas heat fluxes are the dominant processes during epoch-1. Strong coupling between thermocline and sea surface temperature (SST) in epoch-2 indicates that El Niño induced oceanic changes are very significant in the seasonal evolution of basin-wide warming. The thermocline-SST coupling is strengthened by the upward propagating subsurface warming in epoch-2. The westward propagating barrier layer over southern TIO supports persistence of warm SST (over southwest TIO in epoch-2), which in turn induce spring asymmetric mode in winds and precipitation. The asymmetric wind pattern and persistent subsidence over maritime continent are primarily responsible for stronger spring warming in epoch-2. The strong east equatorial Indian Ocean cooling in epoch-2 is mainly driven by coastal upwelling over Java–Sumatra coast, whereas in epoch-1 the weak cooling is controlled by the latent heat flux. The spatiotemporal changes in TIO SST warming and their evolution have strong impact on atmospheric circulation and rainfall distribution over the Indian Oceanic rim through local air–sea interaction. 相似文献
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A study on the variability of atmospheric and oceanic processes over the Arabian Sea during contrasting monsoons 总被引：1，自引：0，他引：1
J. S. Chowdary C. Gnanaseelan S. K. Sinha B. Thompson 《Meteorology and Atmospheric Physics》2006,94(1-4):65-85
Summary The atmospheric and oceanic conditions associated with the southwest monsoon during the contrasting monsoon years of 2002
and 2003 over the Arabian Sea have been analyzed in the present study. Early onset of southwesterlies and reduced net heat
gain due to low solar radiation were responsible for low sea-surface temperatures (SSTs) over the Arabian Sea during 2002
pre-monsoon (particularly in May). Conversely, light winds and an increased net heat gain set up the pre-monsoon warming in
2003. The development and intensification of deep convection over a large area of the Arabian Sea prior to the onset of the
monsoon was observed during 2003, but was absent in 2002. Weak cross equatorial flow and a weak low level jet over the Arabian
Sea reduced moisture transport towards the Indian subcontinent in July 2002. This scenario helped to contribute to a prolonged
break in monsoon conditions during July. However, no such break in conditions occurred during July 2003. In 2002, the summer
monsoon cooling of the Arabian Sea occurred well before July, whereas in 2003 cooling occurred during July. Estimates of wind
driven Ekman (horizontal) and vertical transports showed maximum values in the month of June (July) in 2002 (2003). These
estimates clearly show the importance of horizontal and vertical advection in the summer cooling of the Arabian Sea.
During the southwest monsoon period, the Arabian Sea was warmer in 2003 than in 2002. Late onset of the southwesterlies in
June, late cooling of the Arabian Sea in July, and downwelling Rossby wave propagation were responsible for the warm SSTs
in 2003. Weak wind stress curl in July dampened the westward propagating sea surface height anomaly signals (Rossby waves)
before they reached the western Arabian Sea in 2002, whereas, in 2003 strong wind stress curl enhanced Rossby wave propagation.
During the summer monsoon period, subsurface temperatures in the south central Arabian Sea were warmer in 2003 than in 2002,
particularly in July and August. Strong Ekman convergence, solar penetration, and downwelling (downward velocities) are responsible
for the enhanced subsurface warming in 2003. 相似文献