Climatology and Interannual Variability in the Intensity of Synoptic-Scale Processes in the North Atlantic from the NCEP–NCAR Reanalysis Data

Abstract

North Atlantic synoptic-scale processes are analyzed by bandpassing 6-hourly NCEP-NCAR reanalysis data for several synoptic ranges corresponding to ultrahigh-frequency variability (0.5-2 days), synopticscale variability (2-6 days), slow synoptic processes (6-12 days), and low-frequency variability (12-30 days). Climatological patterns of the intensity of synoptic processes are not collocated for different ranges of variability, especially in the lower troposphere. Intensities of synoptic processes demonstrate opposite trends between the North American coast and in the northeast Atlantic. Although north of 40ЊN the intensity of ultrahigh-frequency variability and synoptic-scale processes show similar interannual variability, further analysis indicates that secular changes, and decadal-scale and interannual variability in the intensities of synoptic processes may not be necessarily consistent for different synoptic timescales. Magnitudes of winter ultrahigh-frequency variability are highly correlated with the intensity of synoptic-scale processes in the 1960s and early 1970s. However, they show little agreement with each other during the last two decades, pointing to the remarkable change in atmospheric variability over the North Atlantic in late 1970s. North Atlantic ultrahigh-frequency variability in winter is highly correlated with surface temperature gradient anomalies in the Atlantic-American sector. These gradients are computed from the merged fields of SST and surface temperature over the continent. They demonstrate a dipolelike pattern associated with the North American coast on one hand, with the subpolar SST front and continental Canada on the other. High-frequency variability and its synoptic counterpart demonstrate different relationships with the North Atlantic Oscillation. Reliability of these results and their sensitivity to the filtering procedures are addressed by comparison to radiosonde data and application of alternative filters.

Extra-tropical cyclones in the present and future climate: a review

“…The standard deviation of this quantity, frequently entitled "storm track", gives a gross representation of the combined intensities and frequencies of low-pressure and high-pressure systems. It is robust against step-like non-climatic shifts in the data, similar to the recent approach of Wang et al (2006b) Aspects of synoptic variability are also found in neighboring frequency bands such as ultrahigh-frequency variability (0.5-2 days) and slow synoptic processes (6-12 days), each associated with climatological patterns usually not collocated with those for the synoptic band (Ayrault et al 1995;Gulev et al 2002).…”

Effects of the synoptic scale variability on the thermohaline circulation

“…The spectrum of variability of this model is the typical one corresponding to a chaotic system. However, synoptic-scale spectrum is very different from chaotic spectrum (Gulev et al, 2002) and therefore the output of the Lorenz model can not be interpreted as synoptic scale variability in our case. To introduce the synoptic variability inside this model, i.e.…”

Changes in storminess on the western coast of Estonia in relation to large-scale atmospheric circulation

“…Some studies indicate no significant trends in cyclone activity and storminess over the Atlantic/European sector (WASA Group 1998, Bijl et al 1999, Gulev et al 2001, Houghton et al 2001). Other studies demonstrate increasing winter storminess in northern Europe since the 1960s (Alexandersson et al 1998, Ulbrich & Christoph 1999, Gulev et al 2002, Paciorek et al 2002, Pryor & Barthelmie 2003, Zhang et al 2004. A northward shift of the winter storm track has been observed during recent decades (Orlanski 1998, Sickmöller et al 2000, McCabe et al 2001.…”