Geoff K. Vallis

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[1] The North Atlantic Oscillation (NAO) has a profound effect on winter climate variability around the Atlantic basin. Strengthening of the NAO in recent decades has altered surface climate in these regions at a rate far in excess of global mean warming. However, only weak NAO trends are reproduced in climate simulations of the 20th Century, even with(More)
Most of the principal qualitative features of the El Niño-Southern Oscillation phenomenon can be explained by a simple but physically motivated theory. These features are the occurrence of sea-surface warmings in the eastern equatorial Pacific and the associated trade wind reversal; the aperiodicity of these events; the preferred onset time with respect to(More)
Observed secular changes in the El Niño / Southern Oscillation (ENSO) phenomenon are not well understood; nor are the major differences in ENSO simulations found among state-of-the-art general circulation models of the tropical Pacific. To address these issues, this study advances an efficient numerical model of the ocean-atmosphere system and then uses it(More)
Convection cannot be explicitly resolved in general circulation models given their typical grid size of 50 km or larger. However, by multiplying the vertical acceleration in the equation of motion by a constant larger than unity, the horizontal scale of convection can be increased at will, without necessarily affecting the larger-scale flow. The resulting(More)
An analytical model of subtropical mode water is presented, based on ventilated thermocline theory and on numerical solutions of a planetary geostrophic basin model. In ventilated thermocline theory, the western pool is a region bounded on the east by subsurface streamlines that outcrop at the western edge of the interior, and in which additional dynamical(More)
From 1982 to 1993, four hundred and sixty transthoracic biopsies were performed to diagnose lung lesions. 258/460 examinations (56%) were made under fluoroscopic and 202/460 exams (44%) under CT guidance. All the instrumental examinations were made with fine cyto/histologic needles (21-22G); the pathologist was always present. Lesion features and biopsy(More)