L. de la Torre

Wave Energy Associated with the Variability of the Stratospheric Polar Vortex

Abstract A study is performed on the energetics of planetary wave forcing associated with the variability of the northern winter polar vortex. The analysis relies on a three-dimensional normal mode expansion of the atmospheric general circulation that allows partitioning the total (i.e., kinetic + available potential) atmospheric energy into the energy associated with Rossby and inertio-gravity modes with barotropic and baroclinic vertical structures. The analysis mainly departs from traditional ones in respect to the wave forcing, which is here assessed in terms of total energy amounts associated with the waves instead of heat and momentum fluxes. Such an approach provides a sounder framework than traditional ones based on Eliassen–Palm (EP) flux diagnostics of wave propagation and related concepts of refractive indices and critical lines, which are strictly valid only in the cases of small-amplitude waves and in the context of the Wentzel–Kramers–Brillouin–Jeffries (WKBJ) approximation. Positive (negati...

Baroclinic Rossby Wave Forcing and Barotropic Rossby Wave Response to Stratospheric Vortex Variability

Abstract An analysis is performed on the dynamical coupling between the variability of the extratropical stratospheric and tropospheric circulations during the Northern Hemisphere winter. Obtained results provide evidence that in addition to the well-known Charney and Drazin mechanism by which vertical propagation of baroclinic Rossby waves is nonlinearly influenced by the zonal mean zonal wind, topographic forcing constitutes another important mechanism by which nonlinearity is introduced in the troposphere–stratosphere wave-driven coupled variability. On the one hand, vortex variability is forced by baroclinic Rossby wave bursts, with positive (negative) peaks of baroclinic Rossby wave energy occurring during rapid vortex decelerations (accelerations). On the other hand, barotropic Rossby waves of zonal wavenumbers s = 1 and 3 respond to the vortex state, and strong evidence is presented that such a response is mediated by changes of the topographic forcing due to zonal mean zonal wind anomalies progres...

The Use of Equivalent Temperature to Analyse Climate Variability

Equivalent temperature based in the NCEP/NCAR reanalysis database has been used as a simultaneous measure of temperature and humidity. Its variations during the 1958-1998 added to the effect of the inclusion of satellite data during the late seventies have been analyzed. An increase of the globally averaged equivalent temperature has been detected, the trend has been considerably greater during the first half of the study period and significant differences can be found between continental and oceanic areas. The relation of the trend with four of the main modes of climate variability has been assessed. The North Atlantic Oscillation and the Artic Oscillations are closely related to the equivalent temperature over the North Atlantic basin, extending toward Northern Asia in the second case. El Niño/Southern Oscillation and the Antarctic Oscillation seem to have a more global effect.

Annular versus Nonannular Variability of the Northern Hemisphere Atmospheric Circulation

Abstract The annular variability of the northern winter extratropical circulation is reassessed based on reanalysis data that are dynamically filtered by normal modes. One-half of the variability of the monthly averaged barotropic zonally symmetric circulation of the Northern Hemisphere is statistically distinct from the remaining variability and is represented by its leading empirical orthogonal function (EOF) alone. The daily time series of the circulation anomalies projected onto the leading EOF is highly correlated (r ≥ 0.7) with the lower-stratospheric northern annular mode (NAM) indices showing that annular variability extends from the stratosphere deep into the troposphere. However, the geopotential and wind anomalies associated with the leading principal component (PC1) of the barotropic zonally symmetric circulation are displaced northward relative to the zonal mean anomalies associated with the PC1 of the geopotential height variability at single-isobaric tropospheric levels. The regression patt...