Further Evidence Of The Dominate Role Of Regional Circluation Patterns On Extreme Weather – Heat Wave Frequency Variability Over North America: Two Distinct Leading Modes” By Wu Et Al 2011

We have been alerted to a 2011 paper [h/t to Souleymane Fall and Dallas Staley] that provides additional evidence why the assessment of regional atmospheric circulation patterns (rather than a global average surface temperature trend) should be a primary focus of climate research. It is the multi-decadal prediction of the changes in the statistics of these large scale circulation patterns that is required to make claims of impacts from “climate change” on that time period. As has been discussed; e.g. see

Pielke Sr., R.A., R. Wilby, D. Niyogi, F. Hossain, K. Dairuku, J. Adegoke, G. Kallos, T. Seastedt, and K. Suding, 2012: Dealing  with complexity and extreme events using a bottom-up, resource-based  vulnerability perspective. AGU Monograph on Complexity and  Extreme Events in Geosciences, in press.

there is no predictive skill on this time period.

The new paper is

Wu, Z., H. Lin, J. Li, Z. Jiang, and T. Ma (2012),  Heat wave frequency variability over North America: Two distinct leading modesJ. Geophys. Res., 117, D02102, doi:10.1029/2011JD016908.

with the abstract [highlight added]

Seasonal prediction of heat wave variability is a scientific challenge and of practical importance. This study investigates the heat wave frequency (HWF) variability over North America (NA) during the past 53 summers (1958–2010). It is found that  the NA HWF is dominated by two distinct modes: the interdecadal (ID) mode and the interannual (IA) mode. The ID mode primarily depicts a HWF increasing pattern over most of the NA continent except some western coastal areas. The IA mode resembles a tripole HWF anomaly pattern with three centers over the northwestern, central, and southern NA. The two leading modes have different dynamic structures and predictability sources. The ID mode is closely associated with the prior spring sea surface  temperature anomaly (SSTA) in the tropical Atlantic and tropical western Pacific that can persist throughout the summer, whereas the IA mode is linked to the development of El Niño–Southern Oscillation. A simplified general circulation model is utilized to examine the possible physical mechanism. For the ID mode the tropical Atlantic SSTA can induce a Gill-type response which extends to NA, while the northwestern Pacific SSTA excites a Rossby wave train propagating eastward toward NA. These two flow patterns jointly contribute to the formation of the large-scale circulation anomalies associated with the ID mode. For the IA mode the corresponding circulation anomalies are basically similar to a Pacific-North America pattern. The subsidence associated with high-pressure anomalies warms and dries the boundary layer, inhibiting cloud formation. The resulting surface radiative  heating further warms the surface. For the low-pressure anomalies the situation is just opposite. Through such processes these SSTAs can exert profound influences on the HWF variability over NA.”

The conclusion has the summary text

“Namias [1982, 1983] found that a protracted heat wave during summer was a manifestation of an abnormal form of the general circulation. Hoskins et al. [1983] suggested a theory of positive feedback between the synoptic eddies and the seasonal mean flow. On the basis of the results in this study and those obtained by Hirschi et al. [2010] and Alexander [2010], the physical processes between the circulation anomalies and HWF may be summarized as following. The SSTAs associated with the ID and IA modes trigger the corresponding teleconnection patterns propagating toward NA and excite high- or low-pressure anomalies over the local region. The subsidence associated with high-pressure anomalies warms and dries the boundary layer, inhibiting cloud formation. The resulting surface radiative heating further warms the surface. For the low pressure anomalies, the situation is just opposite. Through such processes, these SSTAs can exert profound influences to the HWF variability over NA.”

The challenge for the IPCC community (as of yet unfulfilled) is to skillfully predict CHANGES in these circulation features.

source of image

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