Monsoon Regimes in the CCSM3

Meehl, Gerald A.; Arblaster, Julie M.; Lawrence, David M.; Seth, Anji; Schneider, Edwin K.; Kirtman, Ben P.; Min, Dughong

doi:10.1175/jcli3745.1

Cited by 81 publications

(52 citation statements)

References 51 publications

(48 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Instead, tropical precipitation maxima reside over the Guinea coast and over the Gulf of Guinea. It has been hypothesized that simulated warmerthan-observed SSTs in the Gulf of Guinea are responsible for excessive rainfall south of the Guinea coast (Meehl et al, 2006). The comparison between CCSM2/T31x3a and CCSM3/T31 corroborates this hypothesis, since the Gulf of Guinea warm bias is much more pronounced in CCSM3/T31 than in CCSM2/T31x3a (cf.…”

Section: Comparisons With Ccsm3/t31supporting

confidence: 52%

The low-resolution CCSM2 revisited: new adjustments and a present-day control run

Prange

2008

Ocean Sci.

View full text Add to dashboard Cite

Abstract. The low-resolution (T31) version of the Community Climate System Model CCSM2.0.1 is revisited and adjusted by deepening the Greenland-Scotland ridge, changing oceanic mixing parameters, and applying a regional freshwater flux adjustment at high northern latitudes. The main purpose of these adjustments is to maintain a robust Atlantic meridional overturning circulation which collapses in the original model release. The paper describes the present-day control run of the adjusted model (referred to as "CCSM2/T31x3a") which is brought into climatic equilibrium by applying a deep-ocean acceleration technique. The accelerated integration is extended by a 100-year synchronous phase. The simulated meridional overturning circulation has a maximum of 14×10 6 m 3 s −1 in the North Atlantic. The CCSM2/T31x3a control run is evaluated against observations and simulations with other climate models. Most shortcomings found in the CCSM2/T31x3a control run are identified as "typical problems" in global climate modelling. Finally, examples (simulation of North Atlantic hydrography, West African monsoon) are shown in which CCSM2/T31x3a has a better simulation skill than the latest low-resolution Community Climate System Model release, CCSM3/T31.

show abstract

Section: Comparisons With Ccsm3/t31supporting

confidence: 52%

The low-resolution CCSM2 revisited: new adjustments and a present-day control run

Prange

2008

Ocean Sci.

View full text Add to dashboard Cite

show abstract

“…CAM3 is designed to produce simulations with reasonable accuracy for various dynamical cores and horizontal resolutions (Collins et al, 2006;Hurrel et al, 2006;Meehl et al, 2006;). For this study semi-Lagrangian dynamical (SLD) core was used at 128×64 horizontal resolution with 26 vertical levels.…”

Section: Description Of the Modelmentioning

confidence: 99%

Sensitivity of the simulated precipitation to changes in convective relaxation time scale

Mishra

Srinivasan

2010

Ann. Geophys.

View full text Add to dashboard Cite

Abstract. The paper describes the sensitivity of the simulated precipitation to changes in convective relaxation time scale (TAU) of Zhang and McFarlane (ZM) cumulus parameterization, in NCAR-Community Atmosphere Model version 3 (CAM3). In the default configuration of the model, the prescribed value of TAU, a characteristic time scale with which convective available potential energy (CAPE) is removed at an exponential rate by convection, is assumed to be 1 h. However, some recent observational findings suggest that, it is larger by around one order of magnitude. In order to explore the sensitivity of the model simulation to TAU, two model frameworks have been used, namely, aquaplanet and actual-planet configurations. Numerical integrations have been carried out by using different values of TAU, and its effect on simulated precipitation has been analyzed.The aqua-planet simulations reveal that when TAU increases, rate of deep convective precipitation (DCP) decreases and this leads to an accumulation of convective instability in the atmosphere. Consequently, the moisture content in the lower-and mid-troposphere increases. On the other hand, the shallow convective precipitation (SCP) and large-scale precipitation (LSP) intensify, predominantly the SCP, and thus capping the accumulation of convective instability in the atmosphere. The total precipitation (TP) remains approximately constant, but the proportion of the three components changes significantly, which in turn alters the vertical distribution of total precipitation production. The vertical structure of moist heating changes from a vertically extended profile to a bottom heavy profile, with the increase of TAU. Altitude of the maximum vertical velocity shifts from upper troposphere to lower troposphere. Similar response was seen Correspondence to: S. K. Mishra (saroj@ucar.edu) in the actual-planet simulations. With an increase in TAU from 1 h to 8 h, there was a significant improvement in the simulation of the seasonal mean precipitation. The fraction of deep convective precipitation was in much better agreement with satellite observations.

show abstract

“…In fact, only a few of the global producing centers for long-range forecasts use these models for operational seasonal forecasting. Since it has been suggested that model performance may be a function of spatial resolution (Meehl et al 2006;Hurrel et al 2009) and ensemble size (Brown and Murphy 1996), other reasons for using two-tiered instead of coupled systems for operational forecasting include that the former system allows for the operational production of higher-resolution seasonal forecasts as well as larger ensemble forecasts since they are computationally less expensive than the latter. Moreover, when skillful SST forecasts are used, two-tiered systems may perform at least equally well as the current coupled systems (Troccoli et al 2008).…”

Section: Introductionmentioning

confidence: 99%

Seasonal Rainfall Prediction Skill over South Africa: One- versus Two-Tiered Forecasting Systems

Landman

DeWitt

Lee

et al. 2012

Weather and Forecasting

View full text Add to dashboard Cite

Forecast performance by coupled ocean-atmosphere or one-tiered models predicting seasonal rainfall totals over South Africa is compared with forecasts produced by computationally less demanding two-tiered systems where prescribed sea surface temperature (SST) anomalies are used to force the atmospheric general circulation model. Two coupled models and one two-tiered model are considered here, and they are, respectively, the ECHAM4.5-version 3 of the Modular Ocean Model (MOM3-DC2), the ECHAM4.5-GML-NCEP Coupled Forecast System (CFSSST), and the ECHAM4.5 atmospheric model that is forced with SST anomalies predicted by a statistical model. The 850-hPa geopotential height fields of the three models are statistically downscaled to South African Weather Service district rainfall data by retroactively predicting 3-month seasonal rainfall totals over the 14-yr period from 1995/96 to 2008/09. Retroactive forecasts are produced for lead times of up to 4 months, and probabilistic forecast performance is evaluated for three categories with the outer two categories, respectively, defined by the 25th and 75th percentile values of the climatological record. The resulting forecast skill levels are also compared with skill levels obtained by downscaling forecasts produced by forcing the atmospheric model with simultaneously observed SST in order to produce a reference forecast set. Downscaled forecasts from the coupled systems generally outperform the downscaled forecasts from the twotiered system, but neither of the two systems outscores the reference forecasts, suggesting that further improvement in operational seasonal rainfall forecast skill for South Africa is still achievable.

show abstract

Monsoon Regimes in the CCSM3

Cited by 81 publications

References 51 publications

The low-resolution CCSM2 revisited: new adjustments and a present-day control run

The low-resolution CCSM2 revisited: new adjustments and a present-day control run

Sensitivity of the simulated precipitation to changes in convective relaxation time scale

Seasonal Rainfall Prediction Skill over South Africa: One- versus Two-Tiered Forecasting Systems

Contact Info

Product

Resources

About