scholarly journals A Comparative Analysis of Change in the First and Second Moment of the PDF of Seasonal Mean 200-mb Heights with ENSO SSTs

2009 ◽  
Vol 22 (6) ◽  
pp. 1412-1423 ◽  
Author(s):  
Bhaskar Jha ◽  
Arun Kumar
Keyword(s):  
Interannual Variability ◽  
General Circulation ◽  
General Circulation Models ◽  
Seasonal Forecast ◽  
Seasonal Predictability ◽  
Second Moment ◽  
Sst Variability ◽  
Atmospheric General Circulation Models ◽  
The Mean ◽  
Probability Density Function Pdf

Abstract Based on simulations from nine different atmospheric general circulation models (AGCMs), a comparative assessment of the influence of ENSO SST variability on the first and second moment of the probability density function (PDF) of 200-mb seasonal mean height is made. This comparison is quantified by regressing the interannual variability in the mean and the spread of the seasonal means against the Niño-3.4 SSTs. Based on the analysis of simulations from multiple AGCMs, it is concluded that the relative impact of interannual variability of SSTs is larger, and more systematic, on the mean of the PDF of 200-mb heights than on its spread. This result implies that seasonal predictability due to SSTs is predominantly a function of its influence on the seasonal mean. Further, for the practice of seasonal predictions, it might be pragmatic to assume that spread of seasonal means stays constant and that the seasonal forecast information resides entirely in the shift of the seasonal mean PDF.

scholarly journals Midlatitude Static Stability in Simple and Comprehensive General Circulation Models

2008 ◽  
Vol 65 (3) ◽  
pp. 1049-1062 ◽  
Author(s):  
Dargan M. W. Frierson
Keyword(s):  
General Circulation ◽  
Thermal Structure ◽  
Strong Support ◽  
General Circulation Models ◽  
Static Stability ◽  
Parameter Range ◽  
Atmospheric General Circulation Models ◽  
The Mean

Abstract The static stability of the extratropical troposphere is examined in two atmospheric general circulation models (GCMs) over idealized boundary conditions, with emphasis on the role of moisture in determining the midlatitude stability. The determination of the static stability is compared within two models: an idealized moist model with simplified representations of radiative transfer and other physical processes, and a comprehensive GCM with full physics. The GCMs are run over a zonally symmetric, fixed sea surface temperature (SST) aquaplanet surface, with a multitude of SST distributions to study the response of the extratropical static stability over a wide parameter range. In both models, the dry static stability averaged over the midlatitudes increases both with increases in the meridional temperature gradients, and with increases in the mean SST. These changes in static stability are compared with both moist theories and dry theories. Dry baroclinic eddy theories are invalid for the entire parameter range in the idealized GCM, and for much of the parameter range considered in the comprehensive GCM. A moist theory, on the other hand, works remarkably well in predicting the midlatitude stability over the entire parameter range for both models. These simulations give strong support for the influence of moisture on the thermal structure of the midlatitudes.

Successive Modulation of ENSO to the Future Greenhouse Warming

2008 ◽  
Vol 21 (1) ◽  
pp. 3-21 ◽  
Author(s):  
Soon-Il An ◽  
Jong-Seong Kug ◽  
Yoo-Geun Ham ◽  
In-Sik Kang
Keyword(s):  
General Circulation ◽  
Southern Oscillation ◽  
General Circulation Models ◽  
Tropical Pacific ◽  
Greenhouse Warming ◽  
Delayed Response ◽  
Subsurface Temperature ◽  
Climate System Model ◽  
The Mean ◽  
The Tropical Pacific

Abstract The multidecadal modulation of the El Niño–Southern Oscillation (ENSO) due to greenhouse warming has been analyzed herein by means of diagnostics of Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) coupled general circulation models (CGCMs) and the eigenanalysis of a simplified version of an intermediate ENSO model. The response of the global-mean troposphere temperature to increasing greenhouse gases is more likely linear, while the amplitude and period of ENSO fluctuates in a multidecadal time scale. The climate system model outputs suggest that the multidecadal modulation of ENSO is related to the delayed response of the subsurface temperature in the tropical Pacific compared to the response time of the sea surface temperature (SST), which would lead a modulation of the vertical temperature gradient. Furthermore, an eigenanalysis considering only two parameters, the changes in the zonal contrast of the mean background SST and the changes in the vertical contrast between the mean surface and subsurface temperatures in the tropical Pacific, exhibits a good agreement with the CGCM outputs in terms of the multidecadal modulations of the ENSO amplitude and period. In particular, the change in the vertical contrast, that is, change in difference between the subsurface temperature and SST, turns out to be more influential on the ENSO modulation than changes in the mean SST itself.

The Last Interglaciation in Northeast Siberia

1995 ◽  
Vol 43 (2) ◽  
pp. 147-158 ◽  
Author(s):  
Anatoly V. Lozhkin ◽  
Patricia M. Anderson
Keyword(s):  
General Circulation ◽  
General Circulation Models ◽  
The Arctic ◽  
The North ◽  
River Terraces ◽  
Atmospheric General Circulation ◽  
Winter Temperatures ◽  
Atmospheric General Circulation Models ◽  
Arctic Coast ◽  
Organic Deposits

AbstractAlluvial, fluvial, and organic deposits of the last interglaciation are exposed along numerous river terraces in northeast Siberia. Although chronological control is often poor, the paleobotanical data suggest range extensions of up to 1000 km for the primary tree species. These data also indicate that boreal communities of the last interglaciation were similar to modern ones in composition, but their distributions were displaced significantly to the north-northwest. Inferences about climate of this period suggest that mean July temperatures were warmer by 4 to 8°C, and seasonal precipitation was slightly greater. Mean January temperatures may have been severely cooler than today (up to 12°C) along the Arctic coast, but similar or slightly warmer than present in other areas. The direction and magnitude of change in July temperatures agree with Atmospheric General Circulation Models, but the 126,000-year-B.P. model results also suggest trends opposite to the paleobotanical data, with simulated cooler winter temperatures and drier conditions than present during the climatic optimum.

scholarly journals Importance of the advection scheme for the simulation of water isotopes over Antarctica by general circulation models: a case study with LMDZ-iso (LMDZ5a revision 1750)

2017 ◽  
Author(s):  
Alexandre Cauquoin ◽  
Camille Risi
Keyword(s):  
General Circulation ◽  
General Circulation Models ◽  
Temperature Relationship ◽  
Water Isotopes ◽  
Good Representation ◽  
Advection Scheme ◽  
Atmospheric General Circulation ◽  
Atmospheric General Circulation Models ◽  
Polar Water

Abstract. Atmospheric general circulation models (AGCMs) are known to have a warm and isotopically enriched bias over Antarctica. We test here the hypothesis that these biases are consequences of a too diffusive advection. Using the LMDZ-iso model, we show that a good representation of the advection, especially on the horizontal, is very important to reduce the bias in the isotopic contents of precipitation above this area and to improve the modelled water isotopes – temperature relationship. A good advection scheme is thus essential when using GCMs for paleoclimate applications based on polar water isotopes.

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