Extratropical low-frequency variability in a three-level quasi-geostrophic atmospheric model with different spectral resolution

Journal of Geophysical Research: Atmospheres 108:5 (2003)

Authors:

A Weisheimer, MV Kurgansky, K Dethloff, D Handorf

Abstract:

Apart from variations of external forcing components and interactions between climate subsystems, natural atmospheric fluctuations with periods of years, decades and centuries can also be generated by inherent atmospheric dynamical instabilities of the flow. The objective of this study is to investigate the spatial and temporal structure of internal low-frequency atmospheric variability of the Northern Hemisphere using a minimum-complexity model of the extratropical circulation. Here, the main focus is the influence of varying spectral horizontal resolution on the formation of dominant patterns of variability. For this purpose, a three-level quasi-geostrophic atmospheric model with idealized thermal and orographic forcing has been integrated over 1,000 years under perpetual winter conditions with T5, T10, T15, and T21 resolutions. It has been shown that for the crude resolution T5 a rather strong bias occurs, whereas starting with T1O resolution, the nonlinear feedback between large- and small-scale features is reasonably well described. At this resolution a sort of plateau in the model performance has been reached, in respect to both the model climatology and the spatiotemporal structure of variability. Ultralow-frequency variability is most pronounced in the model's stratosphere and is associated with changes in the polar vortex strength and shape caused by vertically propagating planetary waves. Rossby wave trains in the lee of the model large-scale orography are the most dominant structures of long-period fluctuations in the middle troposphere. The results show that interannual- and decadal-scale variations can, in substantial part, be considered as a manifestation of the natural variability of the extratropical atmosphere. The inclusion of a seasonal cycle of the model's diabatic heating increases the interannual and interdecadal variability.

An investigation on total ozone over western Mediterranean

Nuovo Cimento della Societa Italiana di Fisica C 26:1 (2003) 53-60

Authors:

BM Monge-Sanz, GR Casale, S Palmieri, AM Siani

Abstract:

During recent years ozone depletion has been detected not only over polar regions but also over mid-latitude areas. This study analyzed daily total ozone (TO) data from three south-western European locations in order to detect long-time TO trends by means of a filtering technique. Correlation analysis with atmospheric circulation patterns was carried out to explain the decreasing trends observed. Results appear to show a strong correlation between TO decrease and the North Atlantic Oscillation and Arctic Oscillation Indices throughout recent decades. On the other hand, the trends also indicate that, at least during the last ten years, TO variations cannot be explained solely by natural atmospheric cycles over the studied area.

Line-of-sight effects on observability of kink and sausage modes in coronal structures with imaging telescopes

Astronomy & Astrophysics EDP Sciences 397:2 (2003) 765-770

Authors:

FC Cooper, VM Nakariakov, D Tsiklauri

Artificial Neural Networks Applications for Total Ozone Time Series

Springer Nature 2687 (2003) 806-813

Authors:

Beatriz Monge-Sanz, Nicolás Medrano-Marqués

Benefits of increased resolution in the ECMWF ensemble system and comparison with poor-man's ensembles

QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 129:589 (2003) 1269-1288

Authors:

R Buizza, DS Richardson, TN Palmer