scholarly journals GCM Systematic Error Correction and Specification of the Seasonal Mean Pacific–North America Region Atmosphere from Global SSTs

1999 ◽  
Vol 12 (1) ◽  
pp. 273-288 ◽  
Author(s):  
Thomas M. Smith ◽  
Robert E. Livezey
Keyword(s):  
North America ◽  
General Circulation ◽  
Southern Oscillation ◽  
Circulation Model ◽  
Systematic Errors ◽  
Sea Surface ◽  
Average Output ◽  
Surface Temperatures ◽  
Model Variability ◽  
The U.S

Abstract Specifications of 1- and 3-month mean Pacific–North America region 700-hPa heights and U.S. surface temperatures and precipitation, from global sea surface temperatures (SSTs) and the ensemble average output of multiple runs of a general circulation model with the same SSTs prescribed, were explored with canonical correlation analysis. In addition to considerable specification skill, the authors found that 1) systematic errors in SST-forced model variability had substantial linear parts, 2) use of both predictor fields usually enhanced specification performance for the U.S. fields over that for just one of the predictor fields, and 3) skillful specification and model correction of the heights and temperatures were also possible for nonactive or transitional El Niño–Southern Oscillation situations.

scholarly journals An objective tropical Atlantic sea surface temperature gradient index for studies of south Amazon dry-season climate variability and change

2008 ◽  
Vol 363 (1498) ◽  
pp. 1761-1766 ◽  
Author(s):  
Peter Good ◽  
Jason A Lowe ◽  
Mat Collins ◽  
Wilfran Moufouma-Okia
Keyword(s):  
Climate Change ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
General Circulation ◽  
Southern Oscillation ◽  
Circulation Model ◽  
Dry Season ◽  
Sea Surface ◽  
Tropical Atlantic ◽  
Sst Gradient

Future changes in meridional sea surface temperature (SST) gradients in the tropical Atlantic could influence Amazon dry-season precipitation by shifting the patterns of moisture convergence and vertical motion. Unlike for the El Niño-Southern Oscillation, there are no standard indices for quantifying this gradient. Here we describe a method for identifying the SST gradient that is most closely associated with June–August precipitation over the south Amazon. We use an ensemble of atmospheric general circulation model (AGCM) integrations forced by observed SST from 1949 to 2005. A large number of tropical Atlantic SST gradient indices are generated randomly and temporal correlations are examined between these indices and June–August precipitation averaged over the Amazon Basin south of the equator. The indices correlating most strongly with June–August southern Amazon precipitation form a cluster of near-meridional orientation centred near the equator. The location of the southern component of the gradient is particularly well defined in a region off the Brazilian tropical coast, consistent with known physical mechanisms. The chosen index appears to capture much of the Atlantic SST influence on simulated southern Amazon dry-season precipitation, and is significantly correlated with observed southern Amazon precipitation. We examine the index in 36 different coupled atmosphere–ocean model projections of climate change under a simple compound 1% increase in CO 2 . Within the large spread of responses, we find a relationship between the projected trend in the index and the Amazon dry-season precipitation trends. Furthermore, the magnitude of the trend relationship is consistent with the inter-annual variability relationship found in the AGCM simulations. This suggests that the index would be of use in quantifying uncertainties in climate change in the region.

Optimal Tropical Sea Surface Temperature Forcing of North American Drought

2010 ◽  
Vol 23 (14) ◽  
pp. 3907-3917 ◽  
Author(s):  
Sang-Ik Shin ◽  
Prashant D. Sardeshmukh ◽  
Robert S. Webb
Keyword(s):  
Time Series ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North American ◽  
General Circulation ◽  
Southern Oscillation ◽  
Circulation Model ◽  
Sea Surface ◽  
Drought Severity ◽  
Sst Anomaly

Abstract The optimal anomalous sea surface temperature (SST) pattern for forcing North American drought is identified through atmospheric general circulation model integrations in which the response of the Palmer drought severity index (PDSI) is determined for each of 43 prescribed localized SST anomaly “patches” in a regular array over the tropical oceans. The robustness and relevance of the optimal pattern are established through the consistency of results obtained using two different models, and also by the good correspondence of the projection time series of historical tropical SST anomaly fields on the optimal pattern with the time series of the simulated PDSI in separate model integrations with prescribed time-varying observed global SST fields for 1920–2005. It is noteworthy that this optimal drought forcing pattern differs markedly in the Pacific Ocean from the dominant SST pattern associated with El Niño–Southern Oscillation (ENSO), and also shows a large sensitivity of North American drought to Indian and Atlantic Ocean SSTs.

Potential effects of climate change on marine growth and survival of Fraser River sockeye salmon

1995 ◽  
Vol 52 (12) ◽  
pp. 2651-2659 ◽  
Author(s):  
Scott G. Hinch ◽  
Michael C. Healey ◽  
Ron E. Diewert ◽  
Michael A. Henderson ◽  
Keith A. Thomson ◽  
...  
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Sockeye Salmon ◽  
Circulation Model ◽  
Zooplankton Biomass ◽  
Air Pressure ◽  
Sea Surface ◽  
Fraser River ◽  
Sea Surface Temperatures ◽  
Surface Temperatures

Simulation results from the Canadian Climate Centre's atmospheric general circulation model (CCC GCM) coupled to a simplified mixed-layer ocean model predict that doubled atmospheric CO2 concentrations would increase northeast Pacific Ocean sea surface temperatures and weaken existing north–south air pressure gradients. On the basis of predicted changes to air pressure and an empirical relationship between wind-driven upwelling and zooplankton biomass, we calculate that production of food for sockeye salmon (Oncorhynchus nerka) may decrease by 5–9%. We developed empirical relationships between sea surface temperature, zooplankton biomass, adult recruitment, and terminal ocean weight for the early Stuart stock of Fraser River sockeye salmon. Our analyses show that warmer sea surface temperatures, larger adult recruitment, and lower zooplankton biomass are correlated with smaller adult sockeye. Bioenergetics modeling suggests that higher metabolic costs in warmer water coupled with lower food availability could cause the observed reductions in size. Warmer sea surface temperatures during coastal migration by juveniles were correlated with lower recruitment 2 yr later. Warmer sea surface temperatures may be a surrogate for increased levels of predation or decreased food during the juvenile stage. We speculate that Fraser sockeye will be less abundant and smaller if the climate changes as suggested by the Canadian Climate Centre's general circulation model.

scholarly journals On the Relationship between North Atlantic Sea Surface Temperatures and U.S. Hurricane Landfall Risk

2009 ◽  
Vol 48 (1) ◽  
pp. 111-129 ◽  
Author(s):  
Peter S. Dailey ◽  
Gerhard Zuba ◽  
Greta Ljung ◽  
Ioana M. Dima ◽  
Jayanta Guin
Keyword(s):  
General Circulation ◽  
Gulf Coast ◽  
Ocean Basin ◽  
Sea Surface ◽  
Physical Analysis ◽  
Sea Surface Temperatures ◽  
Surface Temperatures ◽  
Complete Life Cycle ◽  
The Relationship ◽  
The U.S

Abstract In the recent literature, considerable attention has been paid to the relationship between climate signals and tropical cyclone activity. Much of the research has focused on Atlantic Ocean basin activity while less attention has been given to landfall frequency and the geographic distribution of risk to life and property. However, recent active seasons like 2004 and 2005 and the resulting damage and economic loss have generated significant interest in the relationship between climate and landfall risk. This study focuses on sea surface temperatures (SST) and examines modulation of landfall activity occurring in anomalously warm-SST seasons. The objective of the study is to evaluate the effect of warmer ocean conditions on U.S. landfall risk. The study is broken into two parts–—statistical and physical. The statistical analysis categorizes historical hurricane seasons as either warm or cool and then estimates shifts in landfall frequency under these two climate modes. The analysis is carried out for overall U.S. landfall risk and then for logical subregions along the U.S. coastline. The climatological behavior for warm-SST conditions is developed across the intensity spectrum, from weak tropical storms to major hurricanes, using wind speed as an intensity measure. The analysis suggests that landfall risk is sensitive to SST conditions but that sensitivity varies by region and intensity. The uncertainty associated with these estimates is discussed. The physical analysis is carried out to understand better why landfall risk is not affected uniformly along the U.S. coastline and to reinforce the reasonability of the statistical results. The study involves a detailed examination of the complete life cycle of historical storms. Results indicate that storms making landfall along the East Coast have different genesis and intensification characteristics relative to storms making landfall along the Gulf Coast. As SSTs warm, the genesis pattern shifts, greatly influencing regional landfall risk. Further, hurricane landfalls may react not only to warm-SST conditions, but also to the effect of ocean temperature anomalies on the atmosphere’s general circulation. There are implications that complex feedback mechanisms play a role in modulating the probability of landfall, especially from certain parts of the Atlantic basin. Such physical theories provide added confidence in statistical estimates of elevated risk for certain breeds of tropical cyclones.

scholarly journals Real World and Tropical Cyclone World. Part II: Sensitivity of Tropical Cyclone Formation to Uniform and Meridionally Varying Sea Surface Temperatures under Aquaplanet Conditions

2020 ◽  
Vol 33 (4) ◽  
pp. 1473-1486 ◽  
Author(s):  
K. J. E. Walsh ◽  
S. Sharmila ◽  
M. Thatcher ◽  
S. Wales ◽  
S. Utembe ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Wind Shear ◽  
General Circulation ◽  
Vertical Wind Shear ◽  
Circulation Model ◽  
Static Stability ◽  
Sea Surface ◽  
Sea Surface Temperatures ◽  
Tropical Cyclone Formation ◽  
Surface Temperatures

AbstractThis study aims to investigate the response of simulated tropical cyclone formation to specific climate conditions, using an idealized aquaplanet framework of an ~40-km-horizontal-resolution atmospheric general circulation model. Two sets of idealized model experiments have been performed, one with a set of uniformly distributed constant global sea surface temperatures (SSTs) and another in which varying meridional SST gradients are imposed. The results show that the strongest relationship between climate and tropical cyclone formation is with vertical static stability: increased static stability is strongly associated with decreased tropical cyclone formation. Vertical wind shear and midtropospheric vertical velocity also appear to be related to tropical cyclone formation, although below a threshold value of wind shear there appears to be little relationship. The relationship of tropical cyclone formation with maximum potential intensity and mean sea surface temperature is weak and not monotonic. These simulations strongly suggest that vertical static stability should be part of any climate theory of tropical cyclone formation.

Tropical-ocean-atmosphere interactions in a coupled model

1989 ◽  
Vol 329 (1604) ◽  
pp. 207-223 ◽  
Keyword(s):  
Pacific Ocean ◽  
General Circulation ◽  
Southern Oscillation ◽  
Heat Budget ◽  
Circulation Model ◽  
Ocean Model ◽  
Tropical Pacific ◽  
Sea Surface ◽  
Tropical Pacific Ocean ◽  
Tropical Ocean

A high-resolution tropical Pacific Ocean model coupled to a medium-resolution atmospheric general circulation model has been integrated for 2 years. A seasonal cycle was included. The atmospheric model when forced with climatological seasonally varying sea surface temperatures simulates the surface stress and net surface heating over the tropical Pacific Ocean to within the uncertainty in the climatological estimates in these quantities. When coupled, however, the models drift into an annually recurring anomalous state, similar in many respects to the El Nino Southern Oscillation observed in the ocean and atmosphere. The model results emphasize the role of off-equatorial anomalies in temperature, atmospheric heating and wind response. Air—sea heat exchange is found to be dominant in determining sea surface temperature changes in these off-equatorial regions. Both cloud and evaporative feedbacks are important in the anomalous surface heat budget.

scholarly journals What Determines the Position and Intensity of the South Atlantic Anticyclone in Austral Winter?—An AGCM Study

2008 ◽  
Vol 21 (2) ◽  
pp. 214-229 ◽  
Author(s):  
Ingo Richter ◽  
Carlos R. Mechoso ◽  
Andrew W. Robertson
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
South Atlantic ◽  
Sea Surface ◽  
Sea Surface Temperatures ◽  
Model Errors ◽  
Austral Winter ◽  
The South ◽  
Surface Temperatures

Abstract The South Atlantic anticyclone is a major feature of the austral winter climatology. An atmospheric general circulation model (AGCM) is used to study the dynamics of the South Atlantic anticyclone by means of control simulations and experiments to investigate sensitivity to prescribed orography, sea surface temperatures, and soil wetness. The South Atlantic anticyclone in the first control simulation is unrealistically zonally elongated and centered too far west—errors typical of coupled ocean–atmosphere GCMs. Results of the sensitivity experiments suggest that these deficiencies are associated with another family of systematic model errors: the overprediction of convection over the tropical land surfaces, particularly over eastern tropical Africa and India, and the concurrent large-scale westward shift in the divergence center at upper levels and the convergence center at lower levels. The results also confirm the important role of South American and African orography in localizing the South Atlantic anticyclone over the ocean. Other factors, however, like the regional zonal gradients of sea surface temperatures, are found to have only a minor impact on the anticyclone. To further substantiate these findings, the wintertime anticyclone is examined using a revised version of the atmospheric GCM. Improvements are found in both the anticyclone as well as the Asia–African summer monsoon circulations. The results demonstrate the existence of links between intensity and structure of the wintertime South Atlantic anticyclone and the major summer monsoons in the Northern Hemisphere.

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