Role of baroclinic eddies in the low-frequency variability

• Main Author: Arakelian, Ara
• Other Authors: Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), UPMC - Université Paris 6 Pierre et Marie Curie, Francis Codron, Jean-Louis Dufresne
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2013
• Subjects: Baroclinic eddies; Low-frequency variability; eddy-flow interaction; Feedback; Southern Oscillation; Horizontal resolution; ondes baroclines; variabilité basse-fréquence; interaction ondes-écoulement; rétroaction; oscillation australe; résolution horizontale; [PHYS]Physics [physics]; [SDU]Sciences of the Universe [physics]; [PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph]; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology; North Atlantic; North Atlantic oscillation
• Online Access: https://hal.science/tel-01467634; https://hal.science/tel-01467634/document; https://hal.science/tel-01467634/file/phd_arakelian_20130222.pdf

Midlatitude baroclinic eddies, synoptic disturbances period from 2 to 10 days, interact on the low-frequency variability , period longer than ten days. For these periods atmospheric circulation variability is dominated by quasi-stationary structures of large spatial scale, as are the North Atlantic Oscillation (NAO) and Southern Oscillation (AO). On one side, momentum transport by eddiesis is balanced with surface friction and keeping the jet around its position, but on the other, the mean flow organizes these eddies. To understand why annular modes seem to be domiant low-frequency variability, eddy feedbacks to a change of zonal mean flow are studied. Resolution effect on the representation of eddies and variability is explored. At first these interactions are studied using nudged simulations allowing isolate properly the response of baroclinic eddies and momentum flux. The change of eddy propagation allows to highlight the involved mechanisms. It appears a positive feedback in the case of latitudinal jet shift, and negatively to a jet speed variation without latitudinal shift. In a second part, a set of simulations with the IPSL model at varying resolution was used to assess biases of mean state and variability representation but also to highlight the relations between the mean state, the variability, and the response to increased CO2. Aux moyennes latitudes les ondes baroclines, perturbations synoptiques de période allant de 2 à 10 jours, interagissent sur la variabilité basse fréquence de période supérieure à une dizaine de jours. Pour ces périodes la variabilité de la circulation atmosphérique est dominée par des structures quasi-stationnaires de très grandes échelle spatiale, comme le sont l'oscillation nord-atlantique (NAO) et l'oscillation australe (OA). D'un coté le transport de moment par les ondes s'équilibre avec la friction en surface et maintient le jet autour de sa position, mais de l'autre, l'écoulement moyen organise ces ondes. Afin de comprendre pourquoi les modes annulaires semblent être la ...