scholarly journals Storm-Track Activity in IPCC AR4/CMIP3 Model Simulations

2013 ◽  
Vol 26 (1) ◽  
pp. 246-260 ◽  
Author(s):  
Edmund K. M. Chang ◽  
Yanjuan Guo ◽  
Xiaoming Xia ◽  
Minghua Zheng
Keyword(s):  
Seasonal Cycle ◽  
Storm Track ◽  
Coupled Model ◽  
Storm Tracks ◽  
Intergovernmental Panel ◽  
Cmip3 Model ◽  
Model Simulations ◽  
Storm Track Activity ◽  
Highly Correlated ◽  
Ipcc Ar4

Abstract The climatological storm-track activity simulated by 17 Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4)/phase 3 of the Coupled Model Intercomparison Project (CMIP3) models is compared to that in the interim ECMWF Re-Analysis (ERA-Interim). Nearly half of the models show significant biases in storm-track amplitude: four models simulate storm tracks that are either significantly (>20%) too strong or too weak in both hemispheres, while four other models have interhemispheric storm-track ratios that are biased by over 10%. Consistent with previous studies, storm-track amplitude is found to be negatively correlated with grid spacing. The interhemispheric ratio of storm-track activity is highly correlated with the interhemispheric ratio of mean available potential energy, and this ratio is biased in some model simulations due to biases in the midlatitude temperature gradients. In terms of geographical pattern, the storm tracks in most CMIP3 models exhibit an equatorward bias in both hemispheres. For the seasonal cycle, most models can capture the equatorward migration and strengthening of the storm tracks during the cool season, but some models exhibit biases in the amplitude of the seasonal cycle. Possible implications of model biases in storm-track climatology have been investigated. For both hemispheres, models with weak storm tracks tend to have larger percentage changes in storm-track amplitudes over the seasonal cycle. Under global warming, for the NH, models with weak storm tracks tend to project larger percentage changes in storm-track amplitude whereas, for the SH, models with large equatorward biases in storm-track latitude tend to project larger poleward shifts. Preliminary results suggest that CMIP5 model projections also share these behaviors.

scholarly journals An Energetics Study of Wintertime Northern Hemisphere Storm Tracks under 4 × CO2 Conditions in Two Ocean–Atmosphere Coupled Models

2009 ◽  
Vol 22 (3) ◽  
pp. 819-839 ◽  
Author(s):  
Alexandre Laîné ◽  
Masa Kageyama ◽  
David Salas-Mélia ◽  
Gilles Ramstein ◽  
Serge Planton ◽  
...  
Keyword(s):  
Latent Heat ◽  
Northern Hemisphere ◽  
Storm Track ◽  
Coupled Model ◽  
Storm Tracks ◽  
Latent Heating ◽  
Mean Flow ◽  
Coupled Models ◽  
Intergovernmental Panel ◽  
Ocean Atmosphere

Abstract Different possible behaviors of winter Northern Hemisphere storm tracks under 4 × CO2 forcing are considered by analyzing the response of two of the ocean–atmosphere coupled models that were run for the fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC-AR4), namely the Institut Pierre Simon Laplace’s global coupled model (IPSL-CM4) and the Centre National de Recherches Meteorologiques’s coupled ocean–atmosphere model (CNRM-CM3). It is interesting to compare these models due to their very different responses, especially concerning the North Atlantic storm track. A local energetics study of the synoptic variability in both models is performed, derived from the eddy energy equations, including diabatic terms. The ability of both models to simulate the present-day eddy energetics is considered, indicating no major discrepancies. Both models indicate that the primary cause for synoptic activity changes at the western end of the storm tracks is related to the baroclinic conversion process, due to mean temperature gradient changes in some localized regions of the western oceanic basins, but also resulting from changes in the eddy efficiency to convert energy from the mean flow. Farther downstream, latent heat release during the developing and mature stages of eddies becomes an important eddy energy source especially in terms of changes between 4 × CO2 and preindustrial conditions. This diabatic process amplifies the upstream synoptic (hence usually baroclinic) changes, with more and/or stronger storms implying more latent heat being released (and the converse being true for weaker synoptic activity). This amplification is asymmetrical for the models considered under the simulated 4 × CO2 conditions, due to a greater amount of water vapor contained in warmer air and hence the potential for more condensation for a given synoptic activity. The magnitude of the reduced latent heating is attenuated, whereas increased latent heating is strengthened. Ageostrophic geopotential fluxes are also important in relocating eddy kinetic energy, especially in the vertical.

scholarly journals Atmospheric Tides in the Latest Generation of Climate Models*

2014 ◽  
Vol 71 (6) ◽  
pp. 1905-1913 ◽  
Author(s):  
Curt Covey ◽  
Aiguo Dai ◽  
Richard S. Lindzen ◽  
Daniel R. Marsh
Keyword(s):  
Climate Models ◽  
Wave Reflection ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Coupled Model ◽  
Atmospheric Tides ◽  
Free Atmosphere ◽  
Intergovernmental Panel ◽  
Model Simulations ◽  
Numerical Experimentation

Abstract For atmospheric tides driven by solar heating, the database of climate model output used in the most recent assessment report of the Intergovernmental Panel on Climate Change (IPCC) confirms and extends the authors’ earlier results based on the previous generation of models. Both the present study and the earlier one examine the surface pressure signature of the tides, but the new database removes a shortcoming of the earlier study in which model simulations were not strictly comparable to observations. The present study confirms an approximate consistency among observations and all model simulations, despite variation of model tops from 31 to 144 km. On its face, this result is surprising because the dominant (semidiurnal) component of the tides is forced mostly by ozone heating around 30–70-km altitude. Classical linear tide calculations and occasional numerical experimentation have long suggested that models with low tops achieve some consistency with observations by means of compensating errors, with wave reflection from the model top making up for reduced ozone forcing. Future work with the new database may confirm this hypothesis by additional classical calculations and analyses of the ozone heating profiles and wave reflection in Coupled Model Intercomparison Project (CMIP) models. The new generation of models also extends CMIP's purview to free-atmosphere fields including the middle atmosphere and above.

scholarly journals Storm Tracks and Climate Change

2006 ◽  
Vol 19 (15) ◽  
pp. 3518-3543 ◽  
Author(s):  
Lennart Bengtsson ◽  
Kevin I. Hodges ◽  
Erich Roeckner
Keyword(s):  
Climate Change ◽  
Southern Hemisphere ◽  
Climate Model ◽  
Storm Track ◽  
Future Climate ◽  
Eastern Pacific ◽  
Storm Tracks ◽  
Intergovernmental Panel ◽  
Atlantic Sector ◽  
Poleward Shift

Abstract Extratropical and tropical transient storm tracks are investigated from the perspective of feature tracking in the ECHAM5 coupled climate model for the current and a future climate scenario. The atmosphere-only part of the model, forced by observed boundary conditions, produces results that agree well with analyses from the 40-yr ECMWF Re-Analysis (ERA-40), including the distribution of storms as a function of maximum intensity. This provides the authors with confidence in the use of the model for the climate change experiments. The statistical distribution of storm intensities is virtually preserved under climate change using the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A1B scenario until the end of this century. There are no indications in this study of more intense storms in the future climate, either in the Tropics or extratropics, but rather a minor reduction in the number of weaker storms. However, significant changes occur on a regional basis in the location and intensity of storm tracks. There is a clear poleward shift in the Southern Hemisphere with consequences of reduced precipitation for several areas, including southern Australia. Changes in the Northern Hemisphere are less distinct, but there are also indications of a poleward shift, a weakening of the Mediterranean storm track, and a strengthening of the storm track north of the British Isles. The tropical storm tracks undergo considerable changes including a weakening in the Atlantic sector and a strengthening and equatorward shift in the eastern Pacific. It is suggested that some of the changes, in particular the tropical ones, are due to an SST warming maximum in the eastern Pacific. The shift in the extratropical storm tracks is shown to be associated with changes in the zonal SST gradient in particular for the Southern Hemisphere.

scholarly journals Are the Northern Hemisphere Winter Storm Tracks Significantly Correlated?

2004 ◽  
Vol 17 (21) ◽  
pp. 4230-4244 ◽  
Author(s):  
Edmund K. M. Chang
Keyword(s):  
Northern Hemisphere ◽  
Storm Track ◽  
Reanalysis Data ◽  
Storm Tracks ◽  
The Pacific ◽  
Aircraft Observations ◽  
Highly Correlated ◽  
Hemisphere Winter ◽  
Aircraft Data ◽  
Northern Hemisphere Winter

Abstract In this study, the correlation between the Northern Hemisphere winter Pacific and Atlantic storm tracks is examined using the NCEP–NCAR reanalysis and the 40-yr ECMWF Re-Analysis (ERA-40), as well as unassimilated aircraft observations. By examining month-to-month variability in the 250-hPa meridional velocity variance, the correlation between the two storm track peaks is found to be as high as 0.5 during the winters between 1975/76 and 1998/99. Here, it is shown that the correlation between the two storm tracks can be clearly detected from the aircraft data. Further analyses of the reanalysis data show that the correlation can also be seen in other eddy variance and covariance statistics, including the poleward heat flux at the 700-hPa level. The correlation between the two storm tracks, as seen in both reanalysis datasets, is shown to be much weaker during the period 1957/58–1971/72, suggesting a possible regime transition from largely uncorrelated storm tracks to highly correlated storm tracks during the 1970s. However, during this earlier period, the number of aircraft observations is insufficient to verify the low correlation seen in the reanalyses. Thus, low biases in the reanalyses during the earlier period cannot be ruled out. An ensemble of four GCM simulations performed using the GFDL GCM forced by global observed SST variations between 1950 and 1995 has also been examined. The correlation between the two storm tracks in the GCM simulations is much lower (0.18) than that observed, even if the analysis is restricted to the GCM simulations from the period 1975/76–1994/95. A Monte Carlo test shows that the observed correlation and the GCM correlation are statistically distinct at the 1% level. Correlations between the Southern Hemisphere summer Pacific and Atlantic storm tracks have also been examined based on the reanalyses datasets. The results suggest that the amplitude of the SH summer Pacific and Atlantic storm tracks are not significantly correlated, showing that seeding of the Atlantic storm track by the Pacific storm track does not necessarily lead to significant correlations between the two storm tracks.

scholarly journals The response of the Northern Hemisphere storm tracks and jetstreams to climate change in the CMIP3, CMIP5, and CMIP6 climate models

2020 ◽  
Author(s):  
Ben Harvey ◽  
Peter Cook ◽  
Len Shaffrey ◽  
Reinhard Schiemann
Keyword(s):  
Climate Change ◽  
Spatial Pattern ◽  
North Atlantic ◽  
Climate Models ◽  
Climate Model ◽  
Storm Track ◽  
Coupled Model ◽  
Storm Tracks ◽  
Cmip5 Models ◽  
Jet Streams

<p>Understanding and predicting how extratropical cyclones might respond to climate change is essential for assessing future weather risks and informing climate change adaptation strategies. Climate model simulations provide a vital component of this assessment, with the caveat that their representation of the present-day climate is adequate. In this study the representation of the NH storm tracks and jet streams and their responses to climate change are evaluated across the three major phases of the Coupled Model Intercomparison Project: CMIP3 (2007), CMIP5 (2012), and CMIP6 (2019). The aim is to quantity how present-day biases in the NH storm tracks and jet streams have evolved with model developments, and to further our understanding of their responses to climate change.</p><p>The spatial pattern of the present-day biases in CMIP3, CMIP5, and CMIP6 are similar. However, the magnitude of the biases in the CMIP6 models is substantially lower in the DJF North Atlantic storm track and jet stream than in the CMIP3 and CMIP5 models. In summer, the biases in the JJA North Atlantic and North Pacific storm tracks are also much reduced in the CMIP6 models. Despite this, the spatial pattern of the climate change response in the NH storm tracks and jet streams are similar across the CMIP3, CMIP5, and CMIP6 ensembles. The SSP2-4.5 scenario responses in the CMIP6 models are substantially larger than in the corresponding RCP4.5 CMIP5 models, consistent with the larger climate sensitivities of the CMIP6 models compared to CMIP5.</p>

Simulating the Seasonal Cycle of the Northern Hemisphere Storm Tracks Using Idealized Nonlinear Storm-Track Models

2007 ◽  
Vol 64 (7) ◽  
pp. 2309-2331 ◽  
Author(s):  
Edmund K. M. Chang ◽  
Pablo Zurita-Gotor
Keyword(s):  
Northern Hemisphere ◽  
Nonlinear Model ◽  
Seasonal Cycle ◽  
Storm Track ◽  
Stationary Wave ◽  
Storm Tracks ◽  
Stationary Waves ◽  
Mean Flow ◽  
Seasonal Evolution ◽  
Wave Development

Abstract In this study, an idealized nonlinear model is used to investigate whether dry dynamical factors alone are sufficient for explaining the observed seasonal modulation of the Northern Hemisphere storm tracks during the cool season. By construction, the model does an excellent job simulating the seasonal evolution of the climatological stationary waves. Yet even under this realistic mean flow, the seasonal modulation in storm-track amplitude predicted by the model is deficient over both ocean basins. The model exhibits a stronger sensitivity to the mean flow baroclinicity than observed, producing too-large midwinter eddy amplitudes compared to fall and spring. This is the case not only over the Pacific, where the observed midwinter minimum is barely apparent in the model simulations, but also over the Atlantic, where the October/April eddy amplitudes are also too weak when the January amplitude is tuned to be about right. The nonlinear model generally produces stronger eddy amplitude with stronger baroclinicity, even in the presence of concomitant stronger deformation due to the enhanced stationary wave. The same was found to be the case in a simpler quasigeostrophic model, in which the eddy amplitude nearly always increases with baroclinicity, and deformation only limits the maximum eddy amplitude when the baroclinicity is unrealistically weak. Overall, these results suggest that it is unlikely that dry dynamical effects alone, such as deformation, can fully explain the observed Pacific midwinter minimum in eddy amplitude. It is argued that one should take into account the seasonal evolution of the impacts of diabatic heating on baroclinic wave development in order to fully explain the seasonal cycle of the storm tracks. A set of highly idealized experiments that attempts to represent some of the impacts of moist heating is presented in an appendix to suggest that deficiencies in the model-simulated seasonal cycle of both storm tracks may be corrected when these effects, together with observed seasonal changes in mean flow structure, are taken into account.

scholarly journals Toward a Seasonally Ice-Covered Arctic Ocean: Scenarios from the IPCC AR4 Model Simulations

2006 ◽  
Vol 19 (9) ◽  
pp. 1730-1747 ◽  
Author(s):  
Xiangdong Zhang ◽  
John E. Walsh
Keyword(s):  
Twentieth Century ◽  
Sea Ice ◽  
Seasonal Cycle ◽  
First Century ◽  
Multimodel Ensemble ◽  
Model Simulations ◽  
Ice Coverage ◽  
Twenty First Century ◽  
Ipcc Ar4 ◽  
Multiyear Ice

Abstract The sea ice simulations by the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) models for the climate of the twentieth century and for global warming scenarios have been synthesized. A large number of model simulations realistically captured the climatological annual mean, seasonal cycle, and temporal trends of sea ice area over the Northern Hemisphere during 1979–99, although there is considerable scatter among the models. In particular, multimodel ensemble means show promising estimates very close to observations for the late twentieth century. Model projections for the twenty-first century demonstrate the largest sea ice area decreases generally in the Special Report on Emission Scenarios (SRES) A1B and A2 scenarios compared with the B1 scenario, indicating large multimodel ensemble mean reductions of −3.54 ± 1.66 × 105 km2 decade−1 in A1B, −4.08 ± 1.33 × 105 km2 decade−1 in A2, and −2.22 ± 1.11 × 105 km2 decade−1 in B1. The corresponding percentage reductions are 31.1%, 33.4%, and 21.6% in the last 20 yr of the twenty-first century, relative to 1979–99. Furthermore, multiyear ice coverage decreases rapidly at rates of −3.86 ± 2.07 × 105 km2 decade−1 in A1B, −4.94 ± 1.91 × 105 km2 decade−1 in A2, and −2.67 ± 1.7107 × 105 km2 decade−1 in B1, making major contributions to the total ice reductions. In contrast, seasonal (first year) ice area increases by 1.10 ± 2.46 × 105 km2 decade−1, 1.99 ± 1.47 × 105 km2 decade−1, and 1.05 ± 1.9247 × 105 km2 decade−1 in the same scenarios, leading to decreases of 59.7%, 65.0%, and 45.8% of the multiyear ice area, and increases of 14.1%, 27.8%, and 11.2% of the seasonal ice area in the last 20 yr of this century. Statistical analysis shows that many of the models are consistent in the sea ice change projections among all scenarios. The results include an evaluation of the 99% confidence interval of the model-derived change of sea ice coverage, giving a quantification of uncertainties in estimating sea ice changes based on the participating models. Hence, the seasonal cycle of sea ice area is amplified and an increased large portion of seasonally ice-covered Arctic Ocean is expected at the end of the twenty-first century. The very different changes of multiyear and seasonal ice may have significant implications for the polar energy and hydrological budgets and pathways.

scholarly journals CMIP5 Projection of Significant Reduction in Extratropical Cyclone Activity over North America

2013 ◽  
Vol 26 (24) ◽  
pp. 9903-9922 ◽  
Author(s):  
Edmund K. M. Chang
Keyword(s):  
North American ◽  
Storm Track ◽  
Coupled Model ◽  
Cmip5 Models ◽  
Mean Flow ◽  
Projected Change ◽  
Temporal Variance ◽  
Intercomparison Project ◽  
Storm Track Activity ◽  
Projected Changes

Abstract Projections of storm-track changes over the continental United States and southern Canada made by 23 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) have been compared to changes projected by 11 models from phase 3 of CMIP (CMIP3). Overall, under representative concentration pathway 8.5 (RCP8.5) forcing, CMIP5 models project much more significant decreases in North American storm-track activity than CMIP3 models under the Special Report on Emission Scenarios (SRES) A2 scenario, with the largest decrease in summer and the smallest decrease in spring. The decrease is found both in temporal variance and cyclone statistics, with the frequency of strong cyclones projected to decrease by 15.9%, 6.6%, 32.6%, and 16.9% for winter, spring, summer, and fall, respectively. There is a strong consensus among the 23 models regarding the sign of the projected change, with less than 20% of the models projecting changes in the opposite sign in any of the storm-track parameters examined. Nevertheless, there are also significant model-to-model differences in the magnitude of the projected changes. Projected changes in mean flow baroclinicity have also been examined. Model-to-model differences in the projected storm-track change are found to correlate significantly with model-to-model differences in the projected change in a locally defined mean available potential energy (MAPE) across the ensemble of 34 CMIP5 and CMIP3 models, suggesting that the differences in the projected change in local MAPE can partly account for not only the model-to-model differences but also the differences between CMIP5 and CMIP3 projections. Examination of projected precipitation change suggests that models projecting larger decrease in North American storm-track activity also project a farther northward intrusion of the decrease in subtropical precipitation.

Finding Storm Track Activity Metrics That Are Highly Correlated with Weather Impacts. Part I: Frameworks for Evaluation and Accumulated Track Activity

2020 ◽  
Vol 33 (23) ◽  
pp. 10169-10186
Author(s):  
Albert Man-Wai Yau ◽  
Edmund Kar-Man Chang
Keyword(s):  
Large Scale ◽  
Grid Point ◽  
Storm Track ◽  
Systematic Evaluation ◽  
Monthly Precipitation ◽  
Mean Flow ◽  
Near Surface ◽  
Storm Track Activity ◽  
Highly Correlated ◽  
Weather Impacts

AbstractIn the midlatitudes, storm tracks give rise to much of the high-impact weather, including precipitation and strong winds. Numerous metrics have been used to quantify storm track activity, but there has not been any systematic evaluation of how well different metrics relate to weather impacts. In this study, two frameworks have been developed to provide such evaluations. The first framework quantifies the maximum one-point correlation between weather impacts at each grid point and the assessed storm track metric. The second makes use of canonical correlation analysis to find the best correlated patterns and uses these patterns to hindcast weather impacts based on storm track metric anomalies using a leave-N-out cross-validation approach. These two approaches have been applied to assess multiple Eulerian variances and Lagrangian tracking statistics for Europe, using monthly precipitation and a near-surface high-wind index as the assessment criteria. The results indicate that near-surface storm track metrics generally relate more closely to weather impacts than upper-tropospheric metrics. For Eulerian metrics, synoptic time scale eddy kinetic energy at 850 hPa relates strongly to both precipitation and wind impacts. For Lagrangian metrics, a novel metric, the accumulated track activity (ATA), which combines information from both cyclone track frequency and amplitude, is found to be best correlated with weather impacts when spatially filtered 850-hPa vorticity maxima are used to define cyclones. The leading patterns of variability for ATA are presented, demonstrating that this metric exhibits coherent large-scale month-to-month variations that are highly correlated with variations in the mean flow and weather impacts.

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