scholarly journals Albedo Of Snow, Ice Sheets and Snow-Covered Sea Ice In General Circulation Models

1990 ◽  
Vol 14 ◽  
pp. 347
Author(s):  
Susan E. Marshall ◽  
Stephen G. Warren
Keyword(s):  
Grain Size ◽  
Sea Ice ◽  
General Circulation ◽  
Near Infrared ◽  
Climate Model ◽  
Impurity Content ◽  
General Circulation Models ◽  
Radiative Properties ◽  
Snow Albedo ◽  
Physically Based

We have developed a physically-based parameterization for snow albedo, for the visible and near-infrared spectral regions used in general circulation models (GCMs). Snow albedo depends primarily on snow grain size, and also on solar zenith angle, snow thickness, impurity content, and atmospheric transmittance. This parameterization is now available as a Fortran subroutine. Simpler, but less accurate, parameterizations have also been developed which depend only on grain size or thickness. Since GCMs do not compute snow grain size, we also developed a method to estimate grain size based on the air temperature and the snow age. Our parameterization for snow albedo is being incorporated in the NCAR Community Climate Model (CCM) in place of the existing empirical parameterization for snow albedo, to determine the effect of this improvement on the model's performance, and the results will be discussed. However, additional aspects of the treatment of the radiative properties of snow and ice were also capable of improvement and are being changed in the CCM. In particular, it is important to recognize that sea ice is often snow-covered and in that case has an albedo as high as that of snow, and that southern hemisphere sea ice is nearly always snow-covered, even through the melting season. The surface albedo for the Antarctic ice sheet should be about 0.83, but it had been set to 0.71 in the CCM, The CCM has been calculating temperatures too warm over Antarctica, and this low albedo contributed to that error.

scholarly journals Albedo Of Snow, Ice Sheets and Snow-Covered Sea Ice In General Circulation Models

1990 ◽  
Vol 14 ◽  
pp. 347-347
Author(s):  
Susan E. Marshall ◽  
Stephen G. Warren
Keyword(s):  
Grain Size ◽  
Sea Ice ◽  
General Circulation ◽  
Near Infrared ◽  
Climate Model ◽  
Impurity Content ◽  
General Circulation Models ◽  
Radiative Properties ◽  
Snow Albedo ◽  
Physically Based

We have developed a physically-based parameterization for snow albedo, for the visible and near-infrared spectral regions used in general circulation models (GCMs). Snow albedo depends primarily on snow grain size, and also on solar zenith angle, snow thickness, impurity content, and atmospheric transmittance. This parameterization is now available as a Fortran subroutine. Simpler, but less accurate, parameterizations have also been developed which depend only on grain size or thickness. Since GCMs do not compute snow grain size, we also developed a method to estimate grain size based on the air temperature and the snow age.Our parameterization for snow albedo is being incorporated in the NCAR Community Climate Model (CCM) in place of the existing empirical parameterization for snow albedo, to determine the effect of this improvement on the model's performance, and the results will be discussed. However, additional aspects of the treatment of the radiative properties of snow and ice were also capable of improvement and are being changed in the CCM. In particular, it is important to recognize that sea ice is often snow-covered and in that case has an albedo as high as that of snow, and that southern hemisphere sea ice is nearly always snow-covered, even through the melting season. The surface albedo for the Antarctic ice sheet should be about 0.83, but it had been set to 0.71 in the CCM, The CCM has been calculating temperatures too warm over Antarctica, and this low albedo contributed to that error.

scholarly journals How Well Do the CMIP5 Models Simulate the Antarctic Atmospheric Energy Budget?

2015 ◽  
Vol 28 (20) ◽  
pp. 7933-7942 ◽  
Author(s):  
Michael Previdi ◽  
Karen L. Smith ◽  
Lorenzo M. Polvani
Keyword(s):  
Sea Ice ◽  
Energy Budget ◽  
General Circulation ◽  
Climate Model ◽  
General Circulation Models ◽  
Cmip5 Models ◽  
Secondary Importance ◽  
Sea Ice Extent ◽  
Atmospheric Energy ◽  
The Antarctic

Abstract The authors evaluate 23 coupled atmosphere–ocean general circulation models from phase 5 of CMIP (CMIP5) in terms of their ability to simulate the observed climatological mean energy budget of the Antarctic atmosphere. While the models are shown to capture the gross features of the energy budget well [e.g., the observed two-way balance between the top-of-atmosphere (TOA) net radiation and horizontal convergence of atmospheric energy transport], the simulated TOA absorbed shortwave (SW) radiation is too large during austral summer. In the multimodel mean, this excessive absorption reaches approximately 10 W m−2, with even larger biases (up to 25–30 W m−2) in individual models. Previous studies have identified similar climate model biases in the TOA net SW radiation at Southern Hemisphere midlatitudes and have attributed these biases to errors in the simulated cloud cover. Over the Antarctic, though, model cloud errors are of secondary importance, and biases in the simulated TOA net SW flux are instead driven mainly by biases in the clear-sky SW reflection. The latter are likely related in part to the models’ underestimation of the observed annual minimum in Antarctic sea ice extent, thus underscoring the importance of sea ice in the Antarctic energy budget. Finally, substantial differences in the climatological surface energy fluxes between existing observational datasets preclude any meaningful assessment of model skill in simulating these fluxes.

scholarly journals Evaluating climate emulation: fundamental impulse testing of simple climate models

2019 ◽  
Vol 10 (4) ◽  
pp. 729-739 ◽  
Author(s):  
Adria K. Schwarber ◽  
Steven J. Smith ◽  
Corinne A. Hartin ◽  
Benjamin Aaron Vega-Westhoff ◽  
Ryan Sriver
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Chemical Species ◽  
Co2 Concentration ◽  
General Circulation Models ◽  
Climate System ◽  
Physically Based ◽  
Mean Climate ◽  
The Impact

Abstract. Simple climate models (SCMs) are numerical representations of the Earth's gas cycles and climate system. SCMs are easy to use and computationally inexpensive, making them an ideal tool in both scientific and decision-making contexts (e.g., complex climate model emulation, parameter estimation experiments, climate metric calculations, and probabilistic analyses). Despite their prolific use, the fundamental responses of SCMs are often not directly characterized. In this study, we use fundamental impulse tests of three chemical species (CO2, CH4, and black carbon – BC) to understand the fundamental gas cycle and climate system responses of several comprehensive (Hector v2.0, MAGICC 5.3, MAGICC 6.0) and idealized (FAIR v1.0, AR5-IR) SCMs. We find that while idealized SCMs are widely used, they fail to capture the magnitude and timescales of global mean climate responses under emissions perturbations, which can produce biased temperature results. Comprehensive SCMs, which have physically based nonlinear forcing and carbon cycle representations, show improved responses compared to idealized SCMs. Even the comprehensive SCMs, however, fail to capture the response timescales to BC emission perturbations seen recently in two general circulation models. Some comprehensive SCMs also generally respond faster than more complex models to a 4×CO2 concentration perturbation, although this was not evident for lower perturbation levels. These results suggest where improvements should be made to SCMs. Further, we demonstrate here a set of fundamental tests that we recommend as a standard evaluation suite for any SCM. Fundamental impulse tests allow users to understand differences in model responses and the impact of model selection on results.

scholarly journals Contributors to linkage between Arctic warming and East Asian winter climate

2021 ◽  
Author(s):  
Xinping Xu ◽  
Shengping He ◽  
Yongqi Gao ◽  
Botao Zhou ◽  
Huijun Wang
Keyword(s):  
Sea Ice ◽  
General Circulation ◽  
Initial Conditions ◽  
Wave Train ◽  
East Asian ◽  
Surface Air Temperature ◽  
General Circulation Models ◽  
The Arctic ◽  
Winter Climate ◽  
Arctic Warming

AbstractPrevious modelling and observational studies have shown discrepancies in the interannual relationship of winter surface air temperature (SAT) between Arctic and East Asia, stimulating the debate about whether Arctic change can influence midlatitude climate. This study uses two sets of coordinated experiments (EXP1 and EXP2) from six different atmospheric general circulation models. Both EXP1 and EXP2 consist of 130 ensemble members, each of which in EXP1 (EXP2) was forced by the same observed daily varying sea ice and daily varying (daily climatological) sea surface temperature (SST) for 1982–2014 but with different atmospheric initial conditions. Large spread exists among ensemble members in simulating the Arctic–East Asian SAT relationship. Only a fraction of ensemble members can reproduce the observed deep Arctic warming–cold continent pattern which extends from surface to upper troposphere, implying the important role of atmospheric internal variability. The mechanisms of deep Arctic warming and shallow Arctic warming are further distinguished. Arctic warming aloft is caused primarily by poleward moisture transport, which in conjunction with the surface warming coupled with sea ice melting constitutes the surface-amplified deep Arctic warming throughout the troposphere. These processes associated with the deep Arctic warming may be related to the forcing of remote SST when there is favorable atmospheric circulation such as Rossby wave train propagating from the North Atlantic into the Arctic.

scholarly journals Climate hypersensitivity to solar forcing?

2000 ◽  
Vol 18 (5) ◽  
pp. 583-588 ◽  
Author(s):  
W. Soon ◽  
E. Posmentier ◽  
S. Baliunas
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Solar Physics ◽  
Stratospheric Ozone ◽  
General Circulation Models ◽  
Static Stability ◽  
Radiative Properties ◽  
Balance Model ◽  
Solar Forcing ◽  
Solar Uv

Abstract. We compare the equilibrium climate responses of a quasi-dynamical energy balance model to radiative forcing by equivalent changes in CO2, solar total irradiance (Stot) and solar UV (SUV). The response is largest in the SUV case, in which the imposed UV radiative forcing is preferentially absorbed in the layer above 250 mb, in contrast to the weak response from global-columnar radiative loading by increases in CO2 or Stot. The hypersensitive response of the climate system to solar UV forcing is caused by strongly coupled feedback involving vertical static stability, tropical thick cirrus ice clouds and stratospheric ozone. This mechanism offers a plausible explanation of the apparent hypersensitivity of climate to solar forcing, as suggested by analyses of recent climatic records. The model hypersensitivity strongly depends on climate parameters, especially cloud radiative properties, but is effective for arguably realistic values of these parameters. The proposed solar forcing mechanism should be further confirmed using other models (e.g., general circulation models) that may better capture radiative and dynamical couplings of the troposphere and stratosphere.Key words: Meteorology and atmospheric dynamics (climatology · general or miscellaneous) · Solar physics · astrophysics · and astronomy (ultraviolet emissions)

scholarly journals Assessing bias corrections of oceanic surface conditions for atmospheric models

2019 ◽  
Vol 12 (1) ◽  
pp. 321-342 ◽  
Author(s):  
Julien Beaumet ◽  
Gerhard Krinner ◽  
Michel Déqué ◽  
Rein Haarsma ◽  
Laurent Li
Keyword(s):  
Sea Ice ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
General Circulation ◽  
General Circulation Models ◽  
Substantial Improvement ◽  
Sea Surface ◽  
Sea Ice Concentration ◽  
Ice Concentration ◽  
Analogue Method

Abstract. Future sea surface temperature and sea-ice concentration from coupled ocean–atmosphere general circulation models such as those from the CMIP5 experiment are often used as boundary forcings for the downscaling of future climate experiments. Yet, these models show some considerable biases when compared to the observations over present climate. In this paper, existing methods such as an absolute anomaly method and a quantile–quantile method for sea surface temperature (SST) as well as a look-up table and a relative anomaly method for sea-ice concentration (SIC) are presented. For SIC, we also propose a new analogue method. Each method is objectively evaluated with a perfect model test using CMIP5 model experiments and some real-case applications using observations. We find that with respect to other previously existing methods, the analogue method is a substantial improvement for the bias correction of future SIC. Consistency between the constructed SST and SIC fields is an important constraint to consider, as is consistency between the prescribed sea-ice concentration and thickness; we show that the latter can be ensured by using a simple parameterisation of sea-ice thickness as a function of instantaneous and annual minimum SIC.

scholarly journals Interhemispheric differences of mesosphere/lower thermosphere winds and tides investigated from three whole atmosphere models and meteor radar observations

2021 ◽  
Author(s):  
Gunter Stober ◽  
Ales Kuchar ◽  
Dimitry Pokhotelov ◽  
Huixin Liu ◽  
Han-Li Liu ◽  
...  
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Lower Thermosphere ◽  
Winter Season ◽  
General Circulation Models ◽  
Meteor Radar ◽  
Radar Observations ◽  
Seasonal Characteristics

Abstract. Long-term and continuous observations of mesospheric/lower thermospheric winds are rare, but they are important to investigate climatological changes at these altitudes on time scales of several years, covering a solar cycle and longer. Such long time series are a natural heritage of the mesosphere/lower thermosphere climate, and they are valuable to compare climate models or long term runs of general circulation models (GCMs). Here we present a climatological comparison of wind observations from six meteor radars at two conjugate latitudes to validate the corresponding mean winds and atmospheric diurnal and semidiurnal tides from three GCMs, namely Ground-to-Topside Model of Atmosphere and Ionosphere for Aeronomy (GAIA), Whole Atmosphere Community Climate Model Extension (Specified Dynamics) (WACCM-X(SD)) and Upper Atmosphere ICOsahedral Non-hydrostatic (UA-ICON) model. Our results indicate that there are interhemispheric differences in the seasonal characteristics of the diurnal and semidiurnal tide. There also are some differences in the mean wind climatologies of the models and the observations. Our results indicate that GAIA shows a reasonable agreement with the meteor radar observations during the winter season, whereas WACCM-X(SD) shows a better agreement with the radars for the hemispheric zonal summer wind reversal, which is more consistent with the meteor radar observations. The free running UA-ICON tends to show similar winds and tides compared to WACCM-X(SD).

scholarly journals Results from the implementation of the elastic viscous plastic sea ice rheology in HadCM3

2006 ◽  
Vol 3 (4) ◽  
pp. 777-803
Author(s):  
W. Connolley ◽  
A. Keen ◽  
A. McLaren
Keyword(s):  
Sea Ice ◽  
Large Scale ◽  
Climate Model ◽  
Ice Dynamics ◽  
Sea Ice Dynamics ◽  
Future Improvement ◽  
Physically Based ◽  
Solid Foundation ◽  
Hadley Centre ◽  
Better Than

Abstract. We present results of an implementation of the Elastic Viscous Plastic (EVP) sea ice dynamics scheme into the Hadley Centre coupled ocean-atmosphere climate model HadCM3. Although the large-scale simulation of sea ice in HadCM3 is quite good with this model, the lack of a full dynamical model leads to errors in the detailed representation of sea ice and limits our confidence in its future predictions. We find that introducing the EVP scheme results in a worse initial simulation of the sea ice. This paper documents various improvements made to improve the simulation, resulting in a sea ice simulation that is better than the original HadCM3 scheme overall. Importantly, it is more physically based and provides a more solid foundation for future improvement. We then consider the interannual variability of the sea ice in the new model and demonstrate improvements over the HadCM3 simulation.

scholarly journals Tracking Scheme Dependence of Simulated Tropical Cyclone Response to Idealized Climate Simulations

2014 ◽  
Vol 27 (24) ◽  
pp. 9197-9213 ◽  
Author(s):  
Michael Horn ◽  
Kevin Walsh ◽  
Ming Zhao ◽  
Suzana J. Camargo ◽  
Enrico Scoccimarro ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
General Circulation ◽  
Climate Model ◽  
Circulation Model ◽  
General Circulation Models ◽  
Tropical Cyclone Activity ◽  
Model Data ◽  
Cyclone Activity ◽  
Sensitivity Testing

Abstract Future tropical cyclone activity is a topic of great scientific and societal interest. In the absence of a climate theory of tropical cyclogenesis, general circulation models are the primary tool available for investigating the issue. However, the identification of tropical cyclones in model data at moderate resolution is complex, and numerous schemes have been developed for their detection. The influence of different tracking schemes on detected tropical cyclone activity and responses in the Hurricane Working Group experiments is examined herein. These are idealized atmospheric general circulation model experiments aimed at determining and distinguishing the effects of increased sea surface temperature and other increased CO2 effects on tropical cyclone activity. Two tracking schemes are applied to these data and the tracks provided by each modeling group are analyzed. The results herein indicate moderate agreement between the different tracking methods, with some models and experiments showing better agreement across schemes than others. When comparing responses between experiments, it is found that much of the disagreement between schemes is due to differences in duration, wind speed, and formation-latitude thresholds. After homogenization in these thresholds, agreement between different tracking methods is improved. However, much disagreement remains, accountable for by more fundamental differences between the tracking schemes. The results indicate that sensitivity testing and selection of objective thresholds are the key factors in obtaining meaningful, reproducible results when tracking tropical cyclones in climate model data at these resolutions, but that more fundamental differences between tracking methods can also have a significant impact on the responses in activity detected.

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