scholarly journals Impacts of Ocean Surface on the Northward Propagation of the Boreal Summer Intraseasonal Oscillation in the NCEP Climate Forecast System

2009 ◽  
Vol 22 (24) ◽  
pp. 6561-6576 ◽  
Author(s):  
Wanqiu Wang ◽  
Mingyue Chen ◽  
Arun Kumar
Keyword(s):  
Latent Heat ◽  
Intraseasonal Oscillation ◽  
Ocean Surface ◽  
Boreal Summer ◽  
Climate Forecast ◽  
Forecast System ◽  
Climate Forecast System ◽  
Boreal Summer Intraseasonal Oscillation ◽  
Northward Propagation ◽  
Sst Anomalies

Abstract Impacts of the ocean surface on the representation of the northward-propagating boreal summer intraseasonal oscillation (NPBSISO) over the Indian monsoon region are analyzed using the National Centers for Environmental Prediction (NCEP) coupled atmosphere–ocean Climate Forecast System (CFS) and its atmospheric component, the NCEP Global Forecast System (GFS). Analyses are based on forecasts of five strong NPBSISO events during June–September 2005–07. The inclusion of an interactive ocean in the model is found to be necessary to maintain the observed NPBSISO. The atmosphere-only GFS is capable of maintaining the convection that propagates from the equator to 12°N with reasonable amplitude within the first 15 days, after which the anomalies become very weak, suggesting that the atmospheric internal dynamics alone are not sufficient to sustain the anomalies to propagate to higher latitudes. Forecasts of the NPBSISO in the CFS are more realistic, with the amplitude of precipitation and 850-mb zonal wind anomalies comparable to that in observations for the entire 30-day target period, but with slower northward propagation compared to that observed. Further, the phase relationship between precipitation, sea surface temperature (SST), and surface latent heat fluxes associated with the NPBSISO in the CFS is similar to that in the observations, with positive precipitation anomalies following warm SST anomalies, which are further led by positive anomalies of the surface latent heat and solar radiation fluxes into the ocean. Additional experiments with the atmosphere-only GFS are performed to examine the impacts of uncertainties in SSTs. It is found that intraseasonal SST anomalies 2–3 times as large as that of the observational bulk SST analysis of Reynolds et al. are needed for the GFS to produce realistic northward propagation of the NPBSISO with reasonable amplitude and to capture the observed phase lag between SST and precipitation. The analysis of the forecasts and the experiments suggests that a realistic representation of the observed propagation of the oscillation by the NCEP model requires not only an interactive ocean but also an intraseasonal SST variability stronger than that of the bulk SST analysis.

Diagnosis of boreal summer intraseasonal oscillation in high resolution NCEP climate forecast system

2015 ◽  
Vol 46 (9-10) ◽  
pp. 3287-3303 ◽  
Author(s):  
S. Abhik ◽  
P. Mukhopadhyay ◽  
R. P. M. Krishna ◽  
Kiran D. Salunke ◽  
Ashish R. Dhakate ◽  
...  
Keyword(s):  
High Resolution ◽  
Intraseasonal Oscillation ◽  
Boreal Summer ◽  
Climate Forecast ◽  
Forecast System ◽  
Climate Forecast System ◽  
Boreal Summer Intraseasonal Oscillation ◽  
Ncep Climate Forecast System

scholarly journals Simulations of Monsoon Intraseasonal Oscillation Using Climate Forecast System Version 2: Insight for Horizontal Resolution and Moist Processes Parameterization

Atmosphere ◽  
2019 ◽  
Vol 10 (8) ◽  
pp. 429 ◽  
Author(s):  
Snehlata Tirkey ◽  
P. Mukhopadhyay ◽  
R. Phani Murali Krishna ◽  
Ashish Dhakate ◽  
Kiran Salunke
Keyword(s):  
Deep Convection ◽  
Intraseasonal Oscillation ◽  
Horizontal Resolution ◽  
Specific Humidity ◽  
Climate Forecast ◽  
Forecast System ◽  
Climate Forecast System ◽  
The North ◽  
Northward Propagation ◽  
Moist Processes

In the present study, we analyze the Climate Forecast System version 2 (CFSv2) model in three resolutions, T62, T126, and T382. We evaluated the performance of all three resolutions of CFSv2 in simulating the Monsoon Intraseasonal Oscillation (MISO) of the Indian summer monsoon (ISM) by analyzing a suite of dynamic and thermodynamic parameters. Results reveal a slower northward propagation of MISO in all models with the characteristic northwest–southeast tilted rain band missing over India. The anomalous moisture convergence and vorticity were collocated with the convection center instead of being northwards. This affected the northward propagation of MISO. The easterly shear to the north of the equator was better simulated by the coarser resolution models than CFS T382. The low level specific humidity showed improvement only in CFS T382 until ~15° N. The analyses of the vertical profiles of moisture and its relation to rainfall revealed that all CFSv2 resolutions had a lower level of moisture in the lower level (< 850 hPa) and a drier level above. This eventually hampered the growth of deep convection in the model. These model shortcomings indicate a possible need of improvement in moist process parameterization in the model in tune with the increase in resolution.

scholarly journals The Boreal Summer Intraseasonal Oscillation Simulated in the NCEP Climate Forecast System: The Effect of Sea Surface Temperature

2007 ◽  
Vol 135 (5) ◽  
pp. 1807-1827 ◽  
Author(s):  
Kyong-Hwan Seo ◽  
Jae-Kyung E. Schemm ◽  
Wanqiu Wang ◽  
Arun Kumar
Keyword(s):  
Indian Ocean ◽  
Wind Shear ◽  
Intraseasonal Oscillation ◽  
Vertical Wind Shear ◽  
Sea Surface ◽  
Boreal Summer ◽  
Forecast System ◽  
Climate Forecast System ◽  
Northward Propagation ◽  
The Indian Ocean

Abstract Observational evidence has indicated the important role of the interaction of the atmosphere with the sea surface in the development and maintenance of the tropical intraseasonal oscillation (ISO). However, improvements in ISO simulations with fully coupled atmosphere–ocean general circulation models are limited and model dependent. This study further examines the effect of air–sea coupling and the basic-state sea surface temperature (SST) associated with the boreal summer intraseasonal oscillation (BSISO) in a 21-yr free run with the recently developed NCEP coupled Climate Forecast System (CFS) model. For this, the CFS run is compared with an Atmospheric Model Intercomparison Project–type long-term simulation forced by prescribed SST in the NCEP Global Forecast System (GFS) model and flux-corrected version of CFS (referred to as CFSA). The GFS run simulates significantly unorganized BSISO convection anomalies, which exhibit an erroneous standing oscillation. The CFS run with interactive air–sea coupling has limited improvements, including the generation of intraseasonal SST variation preceding the convection anomaly by ∼10 days. However, this simulation still does not show the observed continuous northward propagation over the Indian Ocean due to a cold model bias. The CFSA run removes the cold bias in the Indian Ocean and the simulation of the development and propagation of BSISO anomalies are significantly improved. Enhanced and suppressed convection anomalies exhibit the observed quadrupole-like configuration, and phase relationships between precipitation and surface dynamic and thermodynamic variables for the northward propagation are shown to be coherent and consistent with the observations. It is shown that the surface meridional moisture convergence is an important factor for the northward propagation of the BSISO. On the other hand, both the GFS and CFS runs do not realistically simulate an eastward-propagating equatorial mode. The CFSA run produces a more realistic eastward-propagation mode only over the Indian Ocean and Java Sea due to the improved mean state in SST, low-level winds, and vertical wind shear. Reasons for the failure of farther eastward propagation into the west Pacific in CFSA are discussed. This study reconfirms the significance of air–sea interactions. More importantly, however, the results suggest that in order for the influence of the coupled air–sea interaction to be properly communicated, the mean state SST in the coupled model should be reasonably simulated. This is because the basic-state SST itself acts to sustain BSISO convection and it makes the large-scale dynamical environment (i.e., easterly vertical wind shear or low-level westerly zonal wind) more favorable for the propagation of the moist Rossby–Kelvin wave packet.

scholarly journals Improved Tropical Modes of Variability in the NCEP Climate Forecast System (Version 2) via a Stochastic Multicloud Model

2017 ◽  
Vol 74 (10) ◽  
pp. 3339-3366 ◽  
Author(s):  
B. B. Goswami ◽  
B. Khouider ◽  
R. Phani ◽  
P. Mukhopadhyay ◽  
A. J. Majda
Keyword(s):  
Intraseasonal Variability ◽  
Intraseasonal Oscillation ◽  
Climate Simulation ◽  
Climate Forecast ◽  
Forecast System ◽  
Climate Forecast System ◽  
Convective Systems ◽  
Modes Of Variability ◽  
Environmental Prediction ◽  
Ncep Climate Forecast System

Abstract A stochastic multicloud model (SMCM) convective parameterization, which mimics the interactions at subgrid scales of multiple cloud types, is incorporated into the National Centers for Environmental Prediction (NCEP) Climate Forecast System, version 2 (CFSv2), model (CFSsmcm) in lieu of the preexisting simplified Arakawa–Schubert (SAS) cumulus scheme. A detailed analysis of the tropical intraseasonal variability (TISV) and convectively coupled equatorial waves (CCEW) in comparison with the original (control) model and with observations is presented here. The last 10 years of a 15-yr-long climate simulation are analyzed. Significant improvements are seen in the simulation of the Madden–Julian oscillation (MJO) and most of the CCEWs as well as the Indian summer monsoon (ISM) intraseasonal oscillation (MISO). These improvements appear in the form of improved morphology and physical features of these waves. This can be regarded as a validation of the central idea behind the SMCM according to which organized tropical convection is based on three cloud types, namely, the congestus, deep, and stratiform cloud decks, that interact with each other and form a building block for multiscale convective systems. An adequate accounting of the dynamical interactions of this cloud hierarchy thus constitutes an important requirement for cumulus parameterizations to succeed in representing atmospheric tropical variability. SAS fails to fulfill this requirement, which is evident in the unrealistic physical structures of the major intraseasonal modes simulated by CFSv2 as documented here.

Northward Propagation Mechanisms of the Boreal Summer Intraseasonal Oscillation in the ERA-Interim and SP-CCSM

2013 ◽  
Vol 26 (6) ◽  
pp. 1973-1992 ◽  
Author(s):  
Charlotte A. DeMott ◽  
Cristiana Stan ◽  
David A. Randall
Keyword(s):  
Boundary Layer ◽  
Arabian Sea ◽  
Intraseasonal Oscillation ◽  
Lower Troposphere ◽  
Boreal Summer ◽  
Climate System Model ◽  
Boreal Summer Intraseasonal Oscillation ◽  
Moisture Advection ◽  
Northward Propagation ◽  
Barotropic Vorticity

Abstract Mechanisms for the northward propagation (NP) of the boreal summer intraseasonal oscillation (BSISO) and associated Asian summer monsoon (ASM) are investigated using data from the interim ECMWF Re-Analysis (ERA-Interim, herein called ERAI) and the superparameterized Community Climate System Model (SP-CCSM). Analyzed mechanisms are 1) destabilization of the lower troposphere by sea surface temperature anomalies, 2) boundary layer moisture advection, and boundary layer convergence associated with 3) SST gradients and 4) barotropic vorticity anomalies. Mechanism indices are regressed onto filtered OLR anomaly time series to study their relationships to the intraseasonal oscillation (ISO) and to equatorial Rossby (ER) waves. Northward propagation in ERAI and SP-CCSM is promoted by several mechanisms, but is dominated by boundary layer moisture advection and the barotropic vorticity effect. SST-linked mechanisms are of secondary importance but are nonnegligible. The magnitudes of NP mechanisms vary from the Indian Ocean to the west Pacific Ocean, implying that NP is accomplished by different mechanisms across the study area. SP-CCSM correctly simulates observed NP mechanisms over most of the ASM domain except in the Arabian Sea during the early stages of the monsoon life cycle. Reduced NP in the Arabian Sea arises from weaker-than-observed easterly shear, reducing the effectiveness of the barotropic vorticity mechanism. The ability of SP-CCSM to correctly simulate NP mechanisms in other regions results from the model’s ability to simulate reasonable mean wind and moisture fields, a realistic spectrum of variability, and the capability of convection to respond to boundary layer changes induced by large-scale NP mechanisms.

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