- Our Research
Trends and variability of synoptic systems, Dynamics of baroclinic eddies and storm tracks, Wave/mean flow interactions, Changes in weather extremes under greenhouse-gas forcing
Hsu, Pei-Chun, P. H. Diamond, and S. M. Tobias, (2015): Nonperturbative mean-field theory for minimum enstrophy relaxation. Physical Review E 91(5): 053024.
Hsu, Pei-Chun, and P. H. Diamond, (2015): On calculating the potential vorticity flux. Physics of Plasmas, 22: 032314.
Hsu, Pei-Chun, and P. H. Diamond, (2015): Zonal flow formation in the presence of ambient mean shear. Physics of Plasmas, 22: 022306.
Coherent changes in large-scale thermal structure and baroclinic life cycle of synoptic eddies in the Northern Hemisphere The tropospheric warming during the past decades is inhomogeneous and varies with season. In the winter Northern Hemisphere, the tropospheric warming has been larger at latitudes around 30°N than at the midlatitude (30-60°N). This inhomogeneous warming resulted in an increase in meridional temperature gradient in the lower midlatitudes. We observed a correlated enhancement of the entire baroclinic life cycle of synoptic eddies — including eddy fluxes of heat and momentum, and zonal mean flow — associated with the steepened poleward temperature gradient. By contrast, in the summer Northern Hemisphere, the overall tropospheric warming over the mid- to high-latitude land areas has been accompanied by weakly reduced synoptic eddy activities and circulation.
Increasing trends in covarying synoptic eddy activity and temperature gradient in the upper troposphere and lower stratosphere under global warming The radiative effect of increasing greenhouse gases warms the troposphere and cools the stratosphere, thus increasing the equator-to-pole temperature gradient in the upper troposphere and lower stratosphere (UTLS). We observed increasing trends in the synoptic eddy activity associated with a steepening poleward temperature gradient in mid-latitude UTLS regions during winter/summer in the Southern Hemisphere and during winter in the Northern Hemisphere over the past six decades. Similar tendencies will continue enhancing in the 21st century under warming scenario. Our findings suggest that if greenhouse gas–induced warming and cooling continue to change the equator-to-pole temperature gradient as projected in a warming climate, extratropical synoptic disturbances with larger momentum, heat, and moisture fluxes may change accordingly.