Note that this page will be updated when more results from this project are published. Last updated September, 2022.

I. Introduction

Extratropical cyclones are important ingredients of the global circulation. In the mid-latitudes, cyclones dominate the day-to-day weather variability, and changes in extratropical cyclone activity (ECA, or storm track activity) strongly impact regional climate variations. In the Third National Climate Assessment (NCA3), it was stated that “No change in mid-latitude storm intensity or frequency has been detected.” However, the current state of the art climate models from the 5th Phase of the Climate Model Intercomparison Project (CMIP5) robustly project a significant decrease in ECA over North America under global climate change in all seasons, with significant impacts on precipitation changes over much of the U.S. Recent research by our group has demonstrated a significant decrease in ECA during summer between 1979 and 2014, which is consistent with CMIP5 multi-model projections that the largest percentage decrease in ECA is expected in summer. Given the significant societal impacts of extratropical cyclones and the clear linkage between ECA and climate change, ECA is clearly an important climate indicator to be investigated and included in the NCA process.

II. Quantifying ECA

This page explains how ECA can be quantified

ECA data: Monthly ECA index from 1979 (this will be a link to monthly ECA data that users can download directly from this page – the data will be posted after the papers supported by this grant has been accepted for publication)

III. Some background on ECA and storm track activity

• A review paper on storm track dynamics (Chang et al., 2002)
• Observed inter-decadal variations of the Northern Hemisphere storm tracks (Chang and Fu, 2002)
• Understanding the seasonal cycle of Northern Hemisphere ECA (Chang and Zurita-Gotor, 2007)
• Understanding the spatial distribution of the Northern Hemisphere winter storm tracks (Chang, 2009)
• CMIP5 multi-model projection of global storm track change under global warming (Chang et al., 2012)
• CMIP5 projection of significant reduction in ECA over North America in all 4 seasons (Chang, 2013)
• CMIP5 simulation and projection of US East Coast winter storm change (Colle et al., 2013)
• A review paper on US East Coast extratropical cyclones and impacts (Colle et al., 2015)
• ECA modulation of variability and projected change in California winter precipitation (Chang et al., 2015)
• Observed and projected decrease in Northern Hemisphere ECA in summer and its impacts on maximum temperature (Chang et al., 2016)

IV. Results highlighted in NCA4

The following results based on our research have been highlighted in the 2017 U. S. Global Change Research Program Climate Change Special Report (Volume 1 of NCA4 – the full report can be accessed here):

• Extratropical cyclone activity is projected to change in complex ways under future climate scenarios (Chang, 2013; Colle et al., 2013)
• There are large model-to-model differences among CMIP5 climate models (Chang, 2013; Colle et al., 2013)
• There is uncertainty about future changes in winter extratropical cyclones (ETCs). Thus, the potential effects on winter extreme precipitation events is also uncertain (Colle et al., 2013)
• Summertime ETC activity across North America has decreased since 1979, with a reduction of more than 35% in the number of strong summertime ETCs (Chang et al., 2016)
• Most climate models project a decrease in summer ETC activity during the remainder of the 21^st century. This is potentially relevant to extreme precipitation in the northeastern quadrant of the United States because a large percentage of the extreme precipitation events in this region are caused by ETCs and their associated fronts (Chang et al., 2016)
• … blocking … reducing the number of winter storms in California, causing severe drought conditions (Chang et al., 2015)
• Current global climate models (CMIP5) do in fact predict an increase in ETC frequency over the eastern United States, including the most intense ETCs, under the higher scenario (RCP8.5). However, there are large model-to-model differences (Colle et al., 2013)
• Hemispheric-scale extratropical cyclones may experience a northward shift this century, with some studies projecting an overall decrease in storm number (Colle et al., 2015)
• The research is mixed about strong extratropical storms: studies find potential increases in frequency and intensity in some regions, like within the Northeast (Colle et al., 2013) whereas others project decreases in strong extratropical storms in some regions (see also Chang, 2013)

V, New results after NCA4 supported by this project

• ECA significantly modulates wintertime extreme wind, cold, and precipitation events over the continental US (Ma and Chang, 2017)
• CMIP5 projection of significant increase in the number of extreme extratropical cyclones in the Southern Hemisphere (Chang, 2017)
• CMIP5 projection of significant decrease in the number of extratropical cyclones with extreme winds in the Northern Hemisphere (Chang, 2018)
• Differences in the dynamics governing cyclone related wintertime extreme precipitation events over the Ohio Valley and the Pacific Northwest (Ma et al., 2020)
• Importance of the cyclone-anticyclone pair in the dynamics of atmospheric rivers (Guo et al., 2020)
• Introducing Accumulated Cyclone Track Activity – a new metric for quantifying extratropical cyclone activity that relates well with cyclone impacts on weather and climate (Yau and Chang, 2020)
• Understanding projected change in precipitation over Europe in terms of projected changes in cyclone activity (Chang et al., 2022)

The following results will be updated when they appear in press:

• Estimating the impact of projected changes in extratropical cyclone activity on precipitation change over North America  (submitted, in review)

VI. Contributions to IPCC Assessments

Research of our group has informed previous assessments by the Intergovernmental Panel for Climate Change (IPCC). Results from the following papers have been cited by the Fourth (2007), Fifth (2013), and Sixth (2021) Assessment Reports (AR4, AR5, and AR6):

• Chang, E.K.M., and Y.F. Fu, 2002: Inter-decadal variations in Northern Hemisphere winter storm track intensity. J. Climate, 15, 642-658 (AR4 Ch. 3)
• Chang, E.K.M., and Y.F. Fu, 2003: Using Mean flow change as a proxy to infer interdecadal storm track variability. J. Climate, 16, 2178-2196 (AR4 Ch. 3)
• Chang, E.K.M., 2003: Midwinter suppression of the Pacific storm track activity as seen in aircraft observations. J. Atmos. Sci., 60, 1345-1358 (AR4 Ch.3)
• Harnik, N., and E.K.M. Chang, 2003: Storm track variations as seen in radiosonde observations and reanalysis data. J. Climate, 16, 480-495 (AR4 Ch.3)
• Chang, E.K.M., 2007: Assessing the increasing trend in Northern Hemisphere winter storm track activity using surface ship observations and statistical storm track model. J. Climate, 20, 5607-5628 (AR5 Ch. 2)
• Chang, E.K.M., and Y. Guo, 2007: Is the number of North Atlantic tropical cyclones significantly underestimated prior to the availability of satellite observations? Geophys. Res. Letts., 34, L14801, doi: 10.1029/2007GL030169 (AR5 Ch. 2)
• Chang, E.K.M., Y. Guo, and X. Xia, 2012: CMIP5 multimodel ensemble projection of storm track change under global warming. J. Geophys. Research, 117, D23118, doi:10.1029/2012JD018578 (AR5, Ch. 9, 12, and 14; AR6, Ch. 10)
• Chang, E.K.M., Y. Guo, X. Xia, and M. Zheng, 2013: Storm track activity in IPCC AR4/CMIP3 model simulations. J. Climate, 26, 246-, doi:10.1175/JCLI-D-11-00707.1 (AR5 Ch. 12; AR6, Ch. 8)
• Colle, B.A., Z. Zhang, K.A. Lombardo, E.K.M. Chang, P. Liu, and M. Zhang, 2013: Historical and future predictions of eastern North America and western Atlantic extratropical cyclones in CMIP5 during the cool season, J. Climate, 26, 6882-6903 (AR5 Ch. 9, 11, 12, and 14; AR6, Ch. 11)
• Chang, E.K.M., 2014: Impacts of background field removal on CMIP5 projected changes in Pacific winter cyclone activity, J. Geophys. Res. Atmos., 119, 4626-4639 (AR6 Ch. 11)
• Maloney, E.D., S.J. Camargo, E. Chang, et al., 2014: North American climate in CMIP5 experiments: Part III: Assessment of twenty-first-century projections, J. Climate, 27, 2230-2270 (AR6 Ch. 8)
• Colle, B.A., J.F. Booth, and E.K.M. Chang, 2015: Review of historical and future changes of extratropical cyclones and associated impacts along the U.S. east coast. Current Climate Change Reports, 1, 125-143 (AR6 Ch. 8)
• Chang, E.K.M., and A.M.W. Yau, 2016: Northern Hemisphere winter storm track trends since 1959 derived from multiple reanalysis datasets. Clim. Dyn., 47, 1435-1454 (AR6 Ch. 2, 8, and 11)
• Chang, E.K.M., C.-G. Ma, C. Zheng, and A.M.W. Yau, 2016: Observed and projected decrease in Northern Hemisphere extratropical cyclone activity in summer and its impacts on maximum temperature. Geophys. Res. Lett., 43, 2200-2208 (AR6 Ch. 3, 4, 8, 10, and 11)
• Wang, J., H.-M. Kim, and E.K.M. Chang, 2017: Changes in Northern Hemisphere winter storm tracks under the background of Arctic amplification. J. Climate, 30, 3705-3724 (AR6 Ch. 2, 4, and 8)
• Chang, E.K.M., 2017: Projected significant increase in the number of extreme extratropical cyclones in the Southern Hemisphere, J. Climate, 30, 4915-4935 (AR6 Ch. 4, 11, and 12)
• Chang, E.K.M., 2018: CMIP5 projected change in Northern Hemisphere winter cyclones with associated extreme winds. J. Climate, 31, 6527-6542 (AR6 Ch. 4, 8, and 11)

VII. Acknowledgments

• This research is supported by NASA under grant NNX16AG32G and NOAA under grant NA19OAR4310283
• Some of the research highlighted in sections III to VI have been supported by previous NSF and NOAA grants
• Information provided on this web page are provided by the investigators and do not reflect the official views of NASA, NSF, or NOAA
• The personnel involved in this project are:
  • Edmund Chang, SBU, PI – kar.chang@stonybrook.edu
  • NASA project collaborators:
    • Minghua Zhang, SBU; Sun Wong, NASA/JPL; Anthony Del Genio, NASA/GISS
  • Chen-Geng Ma, Albert Yau, and Rui Zhang, SBU research assistants