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.

scholarly journals Coupled Ocean–Atmosphere Response to Seasonal Modulation of Ocean Color: Impact on Interannual Climate Simulations in the Tropical Pacific

2007 ◽  
Vol 20 (2) ◽  
pp. 353-374 ◽  
Author(s):  
J. Ballabrera-Poy ◽  
R. Murtugudde ◽  
R-H. Zhang ◽  
A. J. Busalacchi
Keyword(s):  
Solar Radiation ◽  
Interannual Variability ◽  
Seasonal Cycle ◽  
General Circulation ◽  
Ocean Color ◽  
Circulation Model ◽  
Enso Events ◽  
Ocean Atmosphere ◽  
Atmosphere Model ◽  
The Impact

Abstract The ability to use remotely sensed ocean color data to parameterize biogenic heating in a coupled ocean–atmosphere model is investigated. The model used is a hybrid coupled model recently developed at the Earth System Science Interdisciplinary Center (ESSIC) by coupling an ocean general circulation model with a statistical atmosphere model for wind stress anomalies. The impact of the seasonal cycle of water turbidity on the annual mean, seasonal cycle, and interannual variability of the coupled system is investigated using three simulations differing in the parameterization of the vertical attenuation of downwelling solar radiation: (i) a control simulation using a constant 17-m attenuation depth, (ii) a simulation with the spatially varying annual mean of the satellite-derived attenuation depth, and (iii) a simulation accounting for the seasonal cycle of the attenuation depth. The results indicate that a more realistic attenuation of solar radiation slightly reduces the cold bias of the model. While a realistic attenuation of solar radiation hardly affects the annual mean and the seasonal cycle due to anomaly coupling, it significantly affects the interannual variability, especially when the seasonal cycle of the attenuation depth is used. The seasonal cycle of the attenuation depth interacts with the low-frequency equatorial dynamics to enhance warm and cold anomalies, which are further amplified via positive air–sea feedbacks. These results also indicate that interannual variability of the attenuation depths is required to capture the asymmetric biological feedbacks during cold and warm ENSO events.

scholarly journals Development of the GEOS-5 atmospheric general circulation model: evolution from MERRA to MERRA2

2014 ◽  
Vol 7 (6) ◽  
pp. 7575-7617 ◽  
Author(s):  
A. Molod ◽  
L. Takacs ◽  
M. Suarez ◽  
J. Bacmeister
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Weather Prediction ◽  
Circulation Model ◽  
Wave Drag ◽  
Atmospheric General Circulation ◽  
Wide Range ◽  
Simulated Climate ◽  
The Impact

Abstract. The Modern-Era Retrospective Analysis for Research and Applications-2 (MERRA2) version of the GEOS-5 Atmospheric General Circulation Model (AGCM) is currently in use in the NASA Global Modeling and Assimilation Office (GMAO) at a wide range of resolutions for a variety of applications. Details of the changes in parameterizations subsequent to the version in the original MERRA reanalysis are presented here. Results of a series of atmosphere-only sensitivity studies are shown to demonstrate changes in simulated climate associated with specific changes in physical parameterizations, and the impact of the newly implemented resolution-aware behavior on simulations at different resolutions is demonstrated. The GEOS-5 AGCM presented here is the model used as part of the GMAO's MERRA2 reanalysis, the global mesoscale "nature run", the real-time numerical weather prediction system, and for atmosphere-only, coupled ocean–atmosphere and coupled atmosphere–chemistry simulations. The seasonal mean climate of the MERRA2 version of the GEOS-5 AGCM represents a substantial improvement over the simulated climate of the MERRA version at all resolutions and for all applications. Fundamental improvements in simulated climate are associated with the increased re-evaporation of frozen precipitation and cloud condensate, resulting in a wetter atmosphere. Improvements in simulated climate are also shown to be attributable to changes in the background gravity wave drag, and to upgrades in the relationship between the ocean surface stress and the ocean roughness. The series of "resolution aware" parameters related to the moist physics were shown to result in improvements at higher resolutions, and result in AGCM simulations that exhibit seamless behavior across different resolutions and applications.

scholarly journals Ocean-sea-ice coupling in a global ocean general circulation model

1997 ◽  
Vol 25 ◽  
pp. 116-120 ◽  
Author(s):  
S. Legutke ◽  
E. Maier-Reimkr ◽  
A. Stössel ◽  
A. Hellbach
Keyword(s):  
Sea Ice ◽  
General Circulation Model ◽  
Ocean Circulation ◽  
General Circulation ◽  
Circulation Model ◽  
Ice Cover ◽  
Ocean General Circulation Model ◽  
Global Ocean ◽  
Ocean General Circulation ◽  
The Impact

A global ocean general circulation model has been coupled with a dynamic thermodynamic sea-ice model. This model has been spun-up in a 1000 year integration using daily atmosphere model data. Main water masses and currents are reproduced as well as the seasonal characteristics of the ice cover of the Northern and Southern Hemispheres. Model results for the Southern Ocean, however, show the ice cover as too thin, and there are large permanent polynyas in the Weddell and Ross Seas. These polynyas are due to a large upward oceanic heat flux caused by haline rejection during the freezing of sea ice. Sensitivity studies were performed to test several ways of treating the sea-surface salinity and the rejected brine. The impact on the ice cover, water-mass characteristics, and ocean circulation are described.

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