A Zonal Wavenumber 3 Pattern of Northern Hemisphere Wintertime Planetary Wave Variability at High Latitudes

2012 ◽  
Vol 25 (19) ◽  
pp. 6756-6769 ◽  
Author(s):  
Haiyan Teng ◽  
Grant Branstator
Keyword(s):  
Northern Hemisphere ◽  
Climate Models ◽  
Linear Trend ◽  
Coupled Model ◽  
Meridional Wind ◽  
Planetary Waves ◽  
Climate System Model ◽  
Past Half Century ◽  
The Pacific ◽  
Zonal Wavenumber

Abstract A prominent pattern of variability of the Northern Hemisphere wintertime tropospheric planetary waves, referred to here as the Wave3 pattern, is identified from the NCEP–NCAR reanalysis. It is worthy of attention because its structure is similar to the linear trend pattern as well as the leading pattern of multidecadal variability of the planetary waves during the past half century. The Wave3 pattern is defined as the second empirical orthogonal function (EOF) of detrended December–February mean 300-hPa meridional wind V300 and denotes a zonal shift of the ridges and troughs of the climatological flow. Although its interannual variance is roughly comparable to that of EOF1 of V300, which represents the Pacific–North America (PNA) pattern, its multidecadal variance is nearly twice as large as that of the PNA. Wave3 is not completely structurally or temporally distinct from the northern annular mode (NAM) but, for some attributes, the linkage of the observed trend to Wave3 is clearer than to NAM. The prominence of the Wave3 pattern is further supported by attributes of many climate models that participated in phase 3 of the Coupled Model Intercomparison Project (CMIP3). In particular, in the Community Climate System Model, version 3 (CCSM3), the Wave3 pattern is present as EOF3 of V300 in both a fully coupled integration and a stand-alone atmospheric integration forced by climatological sea surface temperatures. Its existence in the latter experiment indicates that the pattern can be produced by atmospheric processes alone.

Mechanisms Contributing to the Warming Hole and the Consequent U.S. East–West Differential of Heat Extremes

2012 ◽  
Vol 25 (18) ◽  
pp. 6394-6408 ◽  
Author(s):  
Gerald A. Meehl ◽  
Julie M. Arblaster ◽  
Grant Branstator
Keyword(s):  
United States ◽  
Twentieth Century ◽  
Linear Trend ◽  
Coupled Model ◽  
The United States ◽  
Convective Heating ◽  
Central Pacific ◽  
Southeastern Part ◽  
Climate System Model ◽  
East West

Abstract A linear trend calculated for observed annual mean surface air temperatures over the United States for the second-half of the twentieth century shows a slight cooling over the southeastern part of the country, the so-called warming hole, while temperatures over the rest of the country rose significantly. This east–west gradient of average temperature change has contributed to the observed pattern of changes of record temperatures as given by the ratio of daily record high temperatures to record low temperatures with a comparable east–west gradient. Ensemble averages of twentieth-century climate simulations in the Community Climate System Model, version 3 (CCSM3), show a slight west–east warming gradient but no warming hole. A warming hole appears in only several ensemble members in the Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel dataset and in one ensemble member of simulated twentieth-century climate in CCSM3. In this model the warming hole is produced mostly from internal decadal time-scale variability originating mainly from the equatorial central Pacific associated with the Interdecadal Pacific Oscillation (IPO). Analyses of a long control run of the coupled model, and specified convective heating anomaly experiments in the atmosphere-only version of the model, trace the forcing of the warming hole to positive convective heating anomalies in the central equatorial Pacific Ocean near the date line. Cold-air advection into the southeastern United States in winter, and low-level moisture convergence in that region in summer, contribute most to the warming hole in those seasons. Projections show a disappearance of the warming hole, but ongoing greater surface temperature increases in the western United States compared to the eastern United States.

scholarly journals Northern Hemisphere Stationary Waves in a Changing Climate

2019 ◽  
Vol 5 (4) ◽  
pp. 372-389 ◽  
Author(s):  
Robert C. J. Wills ◽  
Rachel H. White ◽  
Xavier J. Levine
Keyword(s):  
Climate Change ◽  
Atmospheric Circulation ◽  
Northern Hemisphere ◽  
Climate Models ◽  
Regional Climate ◽  
Stationary Wave ◽  
Future Research ◽  
Stationary Waves ◽  
The Pacific ◽  
Longitudinal Variations

Abstract Purpose of Review Stationary waves are planetary-scale longitudinal variations in the time-averaged atmospheric circulation. Here, we consider the projected response of Northern Hemisphere stationary waves to climate change in winter and summer. We discuss how the response varies across different metrics, identify robust responses, and review proposed mechanisms. Recent Findings Climate models project shifts in the prevailing wind patterns, with corresponding impacts on regional precipitation, temperature, and extreme events. Recent work has improved our understanding of the links between stationary waves and regional climate and identified robust stationary wave responses to climate change, which include an increased zonal lengthscale in winter, a poleward shift of the wintertime circulation over the Pacific, a weakening of monsoonal circulations, and an overall weakening of stationary wave circulations, particularly their divergent component and quasi-stationary disturbances. Summary Numerous factors influence Northern Hemisphere stationary waves, and mechanistic theories exist for only a few aspects of the stationary wave response to climate change. Idealized studies have proven useful for understanding the climate responses of particular atmospheric circulation features and should be a continued focus of future research.

scholarly journals Planetary wave activity in the Arctic and Antarctic lower stratospheres during 2007 and 2008

2009 ◽  
Vol 9 (4) ◽  
pp. 14601-14643
Author(s):  
S. P. Alexander ◽  
M. G. Shepherd
Keyword(s):  
Northern Hemisphere ◽  
Planetary Wave ◽  
Travelling Waves ◽  
Maximum Amplitude ◽  
Wave Activity ◽  
Planetary Waves ◽  
The Arctic ◽  
Stationary Waves ◽  
Wave Amplification ◽  
Zonal Wavenumber

Abstract. Temperature data from the COSMIC GPS-RO satellite constellation are used to study planetary wave activity in both polar stratospheres from September 2006 until November 2008. One major and several minor sudden stratospheric warmings (SSWs) were recorded during the boreal winters of 2006/2007 and 2007/2008. Planetary wave morphology is studied using space-time spectral analysis while individual waves are extracted using a linear least squares fitting technique. Results show the planetary wave frequency and zonal wavenumber distribution varying between hemisphere and altitude. Most of the large Northern Hemisphere wave activity is associated with the winter SSWs, while the largest amplitude waves in the Southern Hemisphere occur during spring. Planetary wave activity during the 2006/2007 and 2007/2008 Arctic SSWs is due largely to travelling waves with zonal wavenumbers |s|=1 and |s|=2 having periods of 12, 16 and 23 days and stationary waves with |s|=1 and |s|=2. The latitudinal variation of wave amplification during the two Northern Hemisphere winters is studied. Most planetary waves show different structure and behaviour during each winter. Abrupt changes in the latitude of maximum amplitude of some planetary waves is observed co-incident in time with some of the SSWs.

Evaluation of snow albedo feedback simulated by CMIP6 coupled climate models

2020 ◽  
Author(s):  
jiangling hu ◽  
duoying ji
Keyword(s):  
Climate Change ◽  
Northern Hemisphere ◽  
Land Surface ◽  
Climate Models ◽  
Coupled Model ◽  
Cmip5 Models ◽  
Simulation Research ◽  
Albedo Feedback ◽  
Snow Albedo ◽  
Autumn And Winter

<p>As the land surface warms, a subsequent reduction in snow and ice cover reveals a less reflective surface that absorbs more solar radiation, which further enhances the initial warming. This positive feedback climate mechanism is the snow albedo feedback (SAF), which will exacerbate climate warming and is the second largest contributor to Arctic amplification. Snow albedo feedback will increase the sensitivity of climate change in the northern hemisphere, which affects the accuracy of climate models in simulation research of climate change, and further affects the credibility of future climate prediction results.</p><p>Using the latest generation of climate models from CMIP6 (Coupled Model Intercomparison Project Version 6), we analyze seasonal cycle snow albedo feedback in Northern Hemisphere extratropics. We find that the strongest SAF strength is in spring (mean: -1.34 %K<sup>-1</sup>), second strongest is autumn (mean: -1.01 %K<sup>-1</sup>), the weakest is in summer (mean: -0.18 %K<sup>-1</sup>). Except summer, the SAF strength is approximately 0.15% K<sup>-1</sup> larger than CMIP5 models in the other three seasons. The spread of spring SAF strength (range: -1.09 to -1.37% K<sup>-1</sup>) is larger than CMIP5 models. Oppositely, the spread of summer SAF strength (range: 0.20 to -0.56% K<sup>-1</sup>) is smaller than CMIP5 models. When compared with CMIP5 models, the spread of autumn and winter SAF strength have not changed much.</p>

scholarly journals The Annual Cycle of Northern Hemisphere Storm Tracks. Part I: Seasons

2019 ◽  
Vol 32 (6) ◽  
pp. 1743-1760 ◽  
Author(s):  
B. J. Hoskins ◽  
K. I. Hodges
Keyword(s):  
Northern Hemisphere ◽  
Annual Cycle ◽  
Storm Track ◽  
Lower Troposphere ◽  
Meridional Wind ◽  
Diagnostic Techniques ◽  
Storm Tracks ◽  
The Pacific ◽  
Wide Range ◽  
Close Relationship

Abstract In this paper and Part II a comprehensive picture of the annual cycle of the Northern Hemisphere storm tracks is presented and discussed for the first time. It is based on both feature tracking and Eulerian-based diagnostics, applied to vorticity and meridional wind in the upper and lower troposphere. Here, the storm tracks, as diagnosed using both variables and both diagnostic techniques, are presented for the four seasons for each of the two levels. The oceanic storm tracks retain much of their winter mean intensity in spring with only a small change in their latitude. In the summer they are much weaker, particularly in the Pacific and are generally farther poleward. In autumn the intensities are larger again, comparable with those in spring, but the latitude is still nearer to that of summer. However, in the lower troposphere in the eastern ocean basins the tracking metrics show northern and southern tracks that change little with latitude through the year. The Pacific midwinter minimum is seen in upper-troposphere standard deviation diagnostics, but a richer picture is obtained using tracking. In winter there are high intensities over a wide range of latitudes in the central and eastern Pacific, and the western Pacific has high track density but weak intensity. In the lower troposphere all the diagnostics show that the strength of the Pacific and Atlantic storm tracks are generally quite uniform over the autumn–winter–spring period. There is a close relationship between the upper-tropospheric storm track, particularly that based on vorticity, and tropopause-level winds and temperature gradients. In the lower troposphere, in winter the oceanic storm tracks are in the region of the strong meridional SST gradients, but in summer they are located in regions of small or even reversed SST gradients. However, over North America the lower-tropospheric baroclinicity and the upstream portion of the Atlantic storm track stay together throughout the year.

scholarly journals Detection and Attribution of Observed Changes in Northern Hemisphere Spring Snow Cover

2013 ◽  
Vol 26 (18) ◽  
pp. 6904-6914 ◽  
Author(s):  
David E. Rupp ◽  
Philip W. Mote ◽  
Nathaniel L. Bindoff ◽  
Peter A. Stott ◽  
David A. Robinson
Keyword(s):  
Snow Cover ◽  
Northern Hemisphere ◽  
Climate Models ◽  
Global Climate ◽  
Coupled Model ◽  
Internal Variability ◽  
Global Climate Models ◽  
Anthropogenic Forcing ◽  
Detection And Attribution ◽  
Snow Cover Extent

Abstract Significant declines in spring Northern Hemisphere (NH) snow cover extent (SCE) have been observed over the last five decades. As one step toward understanding the causes of this decline, an optimal fingerprinting technique is used to look for consistency in the temporal pattern of spring NH SCE between observations and simulations from 15 global climate models (GCMs) that form part of phase 5 of the Coupled Model Intercomparison Project. The authors examined simulations from 15 GCMs that included both natural and anthropogenic forcing and simulations from 7 GCMs that included only natural forcing. The decline in observed NH SCE could be largely explained by the combined natural and anthropogenic forcing but not by natural forcing alone. However, the 15 GCMs, taken as a whole, underpredicted the combined forcing response by a factor of 2. How much of this underprediction was due to underrepresentation of the sensitivity to external forcing of the GCMs or to their underrepresentation of internal variability has yet to be determined.

scholarly journals Tropical Atlantic Biases in CCSM4

2012 ◽  
Vol 25 (11) ◽  
pp. 3684-3701 ◽  
Author(s):  
Semyon A. Grodsky ◽  
James A. Carton ◽  
Sumant Nigam ◽  
Yuko M. Okumura
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Coupled Model ◽  
Horizontal Resolution ◽  
Ocean Model ◽  
Tropical Atlantic ◽  
Climate System Model ◽  
Stratocumulus Clouds ◽  
Subtropical Highs ◽  
The Tropics

This paper focuses on diagnosing biases in the seasonal climate of the tropical Atlantic in the twentieth-century simulation of the Community Climate System Model, version 4 (CCSM4). The biases appear in both atmospheric and oceanic components. Mean sea level pressure is erroneously high by a few millibars in the subtropical highs and erroneously low in the polar lows (similar to CCSM3). As a result, surface winds in the tropics are ~1 m s−1 too strong. Excess winds cause excess cooling and depressed SSTs north of the equator. However, south of the equator SST is erroneously high due to the presence of additional warming effects. The region of highest SST bias is close to southern Africa near the mean latitude of the Angola–Benguela Front (ABF). Comparison of CCSM4 to ocean simulations of various resolutions suggests that insufficient horizontal resolution leads to the insufficient northward transport of cool water along this coast and an erroneous southward stretching of the ABF. A similar problem arises in the coupled model if the atmospheric component produces alongshore winds that are too weak. Erroneously warm coastal SSTs spread westward through a combination of advection and positive air–sea feedback involving marine stratocumulus clouds. This study thus highlights three aspects to improve to reduce bias in coupled simulations of the tropical Atlantic: 1) large-scale atmospheric pressure fields; 2) the parameterization of stratocumulus clouds; and 3) the processes, including winds and ocean model resolution, that lead to errors in seasonal SST along southwestern Africa. Improvements of the latter require horizontal resolution much finer than the 1° currently used in many climate models.

Frontal Scale Air–Sea Interaction in High-Resolution Coupled Climate Models

2010 ◽  
Vol 23 (23) ◽  
pp. 6277-6291 ◽  
Author(s):  
Frank O. Bryan ◽  
Robert Tomas ◽  
John M. Dennis ◽  
Dudley B. Chelton ◽  
Norman G. Loeb ◽  
...  
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Climate Models ◽  
Prediction Models ◽  
Weather Prediction ◽  
Surface Wind ◽  
Coupled Model ◽  
Climate System Model ◽  
Surface Wind Stress ◽  
Coupled Climate Models

Abstract The emerging picture of frontal scale air–sea interaction derived from high-resolution satellite observations of surface winds and sea surface temperature (SST) provides a unique opportunity to test the fidelity of high-resolution coupled climate simulations. Initial analysis of the output of a suite of Community Climate System Model (CCSM) experiments indicates that characteristics of frontal scale ocean–atmosphere interaction, such as the positive correlation between SST and surface wind stress, are realistically captured only when the ocean component is eddy resolving. The strength of the coupling between SST and surface stress is weaker than observed, however, as has been found previously for numerical weather prediction models and other coupled climate models. The results are similar when the atmospheric component model grid resolution is doubled from 0.5° to 0.25°, an indication that shortcomings in the representation of subgrid scale atmospheric planetary boundary layer processes, rather than resolved scale processes, are responsible for the weakness of the coupling. In the coupled model solutions the response to mesoscale SST features is strongest in the atmospheric boundary layer, but there is a deeper reaching response of the atmospheric circulation apparent in free tropospheric clouds. This simulated response is shown to be consistent with satellite estimates of the relationship between mesoscale SST and all-sky albedo.

scholarly journals Northern Hemisphere Snow-Cover Trends (1967–2018): A Comparison between Climate Models and Observations

Geosciences ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 135 ◽  
Author(s):  
◽  
◽  
◽  
◽  
◽  
...  
Keyword(s):  
Snow Cover ◽  
Northern Hemisphere ◽  
Climate Models ◽  
Climate Model ◽  
Coupled Model ◽  
Poor Performance ◽  
Four Seasons ◽  
Intercomparison Project ◽  
Autumn And Winter

Observed changes in Northern Hemisphere snow cover from satellite records were compared to those predicted by all available Coupled Model Intercomparison Project Phase 5 (“CMIP5”) climate models over the duration of the satellite’s records, i.e., 1967–2018. A total of 196 climate model runs were analyzed (taken from 24 climate models). Separate analyses were conducted for the annual averages and for each of the seasons (winter, spring, summer, and autumn/fall). A longer record (1922–2018) for the spring season which combines ground-based measurements with satellite measurements was also compared to the model outputs. The climate models were found to poorly explain the observed trends. While the models suggest snow cover should have steadily decreased for all four seasons, only spring and summer exhibited a long-term decrease, and the pattern of the observed decreases for these seasons was quite different from the modelled predictions. Moreover, the observed trends for autumn and winter suggest a long-term increase, although these trends were not statistically significant. Possible explanations for the poor performance of the climate models are discussed.

The Response of Northern Hemisphere Snow Cover to a Changing Climate*

2009 ◽  
Vol 22 (8) ◽  
pp. 2124-2145 ◽  
Author(s):  
Ross D. Brown ◽  
Philip W. Mote
Keyword(s):  
Sensitivity Analysis ◽  
Snow Cover ◽  
Northern Hemisphere ◽  
Climate Sensitivity ◽  
Climate Models ◽  
Snow Water Equivalent ◽  
Coupled Model ◽  
Sensitivity Study ◽  
Snow Accumulation ◽  
Snow Cover Duration

Abstract A snowpack model sensitivity study, observed changes of snow cover in the NOAA satellite dataset, and snow cover simulations from the Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel dataset are used to provide new insights into the climate response of Northern Hemisphere (NH) snow cover. Under conditions of warming and increasing precipitation that characterizes both observed and projected climate change over much of the NH land area with seasonal snow cover, the sensitivity analysis indicated snow cover duration (SCD) was the snow cover variable exhibiting the strongest climate sensitivity, with sensitivity varying with climate regime and elevation. The highest snow cover–climate sensitivity was found in maritime climates with extensive winter snowfall—for example, the coastal mountains of western North America (NA). Analysis of trends in snow cover duration during the 1966–2007 period of NOAA data showed the largest decreases were concentrated in a zone where seasonal mean air temperatures were in the range of −5° to +5°C that extended around the midlatitudinal coastal margins of the continents. These findings were echoed by the climate models that showed earlier and more widespread decreases in SCD than annual maximum snow water equivalent (SWEmax), with the zone of earliest significant decrease located over the maritime margins of NA and western Europe. The lowest SCD–climate sensitivity was observed in continental interior climates with relatively cold and dry winters, where precipitation plays a greater role in snow cover variability. The sensitivity analysis suggested a potentially complex elevation response of SCD and SWEmax to increasing temperature and precipitation in mountain regions as a result of nonlinear interactions between the duration of the snow season and snow accumulation rates.

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