Wave-Breaking Characteristics of Northern Hemisphere Winter Blocking: A Two-Dimensional Approach
JOURNAL OF CLIMATE 26:13 (2013) 4535-4549
On the role of the ocean in projected atmospheric stability changes in the Atlantic polar low region
Geophysical Research Letters 39:24 (2012)
Abstract:
The occurrence of destructive mesoscale 'polar low' cyclones in the subpolar North Atlantic is projected to decline under anthropogenic change, due to an increase in atmospheric static stability. This letter reports on the role of changes in ocean circulation in shaping the atmospheric stability. In particular, the Atlantic Meridional Overturning Circulation (AMOC) is projected to weaken in response to anthropogenic forcing, leading to a local minimum in warming in this region. The reduced warming is restricted to the lower troposphere, hence contributing to the increase in static stability. Linear correlation analysis of the CMIP3 climate model ensemble suggests that around half of the model uncertainty in the projected stability response arises from the varied response of the AMOC between models. © 2012. American Geophysical Union. All Rights Reserved.How large are projected 21st century storm track changes
Geophysical Research Letters 39:17 (2012)
Abstract:
Projected changes in the extra-tropical wintertime storm tracks are investigated using the multi-model ensembles from both the third and fifth phases of the World Climate Research Programme's Coupled Model Intercomparison Project (CMIP3 and CMIP5). The aim is to characterize the magnitude of the storm track responses relative to their present-day year-to-year variability. For the experiments considered, the 'middle-of-the-road' scenarios in each CMIP, there are regions of the Northern Hemisphere where the responses of up to 40% of the models exceed half of the inter-annual variability, and for the SouthernHemisphere there are regions where up to 60% of the model responses exceed half of the inter-annual variability. Citation: Harvey, B. J., L. C. Shaffrey, T. J. Woollings, G. Zappa, and K. I. Hodges (2012), How large are projected 21st century storm track changes?, Geophys. Res. Lett., 39, L18707,. © 2012. American Geophysical Union.Wave-breaking characteristics of midlatitude blocking
Quarterly Journal of the Royal Meteorological Society 138:666 (2012) 1285-1296
Abstract:
In this article, Northern Hemisphere winter midlatitude blocking is analysed through its wave-breaking characteristics. Rossby wave breaking is identified as a key process in blocking occurrence, as it provides the mechanism for the meridional reversal pattern typical of blocking. Two indices are designed to detect the major properties of wave breaking, i.e. the orientation (cyclonic/anticyclonic-direction of breaking or DB index) and the relative contribution of air masses (warm/cold-relative intensity or RI index). The use of the DB index differentiates between the anticyclonic cases over Europe and Asia and the cyclonic events over the oceanic basins. One of the three regions displaying cyclonic type was found over the Atlantic Ocean, the other two being over the Pacific Ocean. The first of these is located over the western side of the Pacific and is dominated by warm air extrusions, whereas the second is placed northward of the exit region of the jet stream, where the meridional θ gradient is much weaker. Two European blocking types have been detected using the RI index, which separates out the cases dominated by warm and cold air masses. The latter cases in particular exhibited a well-structured dipole, with associated strong anomalies in both temperature and precipitation. © 2011 Royal Meteorological Society.A methodology for the comparison of blocking climatologies across indices, models and climate scenarios
Climate Dynamics 38:11-12 (2012) 2467-2481