scholarly journals Influence of Indian Ocean Dipole on boreal summer intraseasonal oscillations in a coupled general circulation model

2009 ◽  
Vol 114 (D6) ◽  
Author(s):  
R. S. Ajayamohan ◽  
Suryachandra A. Rao ◽  
Jing-Jia Luo ◽  
Toshio Yamagata
Keyword(s):  
Indian Ocean ◽  
General Circulation Model ◽  
Indian Ocean Dipole ◽  
General Circulation ◽  
Circulation Model ◽  
Boreal Summer ◽  
Coupled General Circulation Model ◽  
Intraseasonal Oscillations

scholarly journals Termination of Indian Ocean Dipole Events in a Coupled General Circulation Model

2007 ◽  
Vol 20 (13) ◽  
pp. 3018-3035 ◽  
Author(s):  
Suryachandra A. Rao ◽  
Sebastien Masson ◽  
Jing-Jia Luo ◽  
Swadhin K. Behera ◽  
Toshio Yamagata
Keyword(s):  
Indian Ocean ◽  
Solar Radiation ◽  
General Circulation Model ◽  
Indian Ocean Dipole ◽  
General Circulation ◽  
Circulation Model ◽  
Equatorial Indian Ocean ◽  
Coupled General Circulation Model ◽  
Zonal Winds ◽  
Budget Analysis

Abstract Using 200 yr of coupled general circulation model (CGCM) results, causes for the termination of Indian Ocean dipole (IOD) events are investigated. The CGCM used here is the Scale Interaction Experiment-Frontier Research Center for Global Change (SINTEX-F1) model, which consists of a version of the European Community–Hamburg (ECHAM4.6) atmospheric model and a version of the Ocean Parallelise (OPA8.2) ocean general circulation model. This model reproduces reasonably well the present-day climatology and interannual signals of the Indian and Pacific Oceans. The main characteristics of the intraseasonal disturbances (ISDs)/oscillations are also fairly well captured by this model. However, the eastward propagation of ISDs in the model is relatively fast in the Indian Ocean and stationary in the Pacific compared to observations. A sudden reversal of equatorial zonal winds is observed, as a result of significant intraseasonal disturbances in the equatorial Indian Ocean in November–December of IOD events, which evolve independently of ENSO. A majority of these IOD events (15 out of 18) are terminated mainly because of the 20–40-day ISD activity in the equatorial zonal winds. Ocean heat budget analysis in the upper 50 m clearly shows that the initial warming after the peak of the IOD phenomenon is triggered by increased solar radiation owing to clear-sky conditions in the eastern Indian Ocean. Subsequently, the equatorial jets excited by the ISD deepen the thermocline in the southeastern equatorial Indian Ocean. This deepening of the thermocline inhibits the vertical entrainment of cool waters and therefore the IOD is terminated. IOD events that co-occur with ENSO are terminated owing to anomalous incoming solar radiation as a result of prevailing cloud-free skies. Further warming occurs seasonally through the vertical convergence of heat due to a monsoonal wind reversal along Sumatra–Java. On occasion, strong ISD activities in July–August terminated short-lived IOD events by triggering downwelling intraseasonal equatorial Kelvin waves.

scholarly journals Modulation of Tropical Intraseasonal Oscillations by Ocean–Atmosphere Coupling

2006 ◽  
Vol 19 (3) ◽  
pp. 366-391 ◽  
Author(s):  
K. Rajendran ◽  
A. Kitoh
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Circulation Model ◽  
Boreal Summer ◽  
Coupled Modes ◽  
Structure Amplitude ◽  
Ocean Atmosphere ◽  
Intraseasonal Oscillations ◽  
The Impact ◽  
Tropical Intraseasonal Oscillations

Abstract The impact of ocean–atmosphere coupling on the structure and propagation characteristics of 30–60-day tropical intraseasonal oscillations (TISOs) is investigated by analyzing long-term simulations of the Meteorological Research Institute coupled general circulation model (CGCM) and its stand-alone atmospheric general circulation model (AGCM) version forced with SSTs derived from the CGCM and comparing them with recent observation datasets [Global Precipitation Climatology Project (GPCP) precipitation, 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), and Reynolds SST]. Composite events of (i) eastward propagating Madden–Julian oscillations (MJOs) during boreal winter and (ii) northward propagating intraseasonal oscillations (NPISOs) during boreal summer, constructed based on objective criteria, show that the three-dimensional structure, amplitude, and speed of propagation, and the phase relationship among surface fluxes, SST, and convection, are markedly improved in the CGCM simulation. Consistent with the frictional wave conditional instability of the second kind mechanism, successive development of low-level convergence to the east (north) of deep convection was found to be important for eastward (northward) propagation of MJO (NPISO). Complex interaction between large-scale dynamics and convection reveals the importance of atmospheric dynamics and suggests that they are intrinsic modes in the atmosphere where coupling is not essential for their existence. However, as in observations, realistic coupling in the CGCM is found to result in the evolution of TISOs as coupled modes through a coherent coupled feedback process. This acts as an amplifying mechanism for the existing propagating convective anomalies and plays an important modifying role toward a more realistic simulation of TISOs. In contrast, the simulated TISOs in its atmosphere-alone component lack many of the important features associated with their amplitude, phase, and life cycle. Thus, a realistic representation of the interaction between sea surface and the atmospheric boundary layer is crucial for a better simulation of TISOs.

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