Intermittent African Easterly Wave Activity in a Dry Atmospheric Model: Influence of the Extratropics

• Published in: Journal of Climate
• Main Authors: Leroux, Stephanie, Hall, Nicholas M. J., Kiladis, George N.
• Other Authors: National Oceanic and Atmospheric Administration (NOAA), Océan du Large et Variabilité Climatique (OLVAC), Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales Toulouse (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Météo France-Centre National d'Études Spatiales Toulouse (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), NOAA Earth System Research Laboratory (ESRL)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2011
• Subjects: Africa; Tropics; Waves; atmospheric; Monsoons; Summer/warm season; Synoptic-scale processes; General circulation models; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Leroux; North Atlantic
• Online Access: https://hal.archives-ouvertes.fr/hal-00798734; https://hal.archives-ouvertes.fr/hal-00798734/document; https://hal.archives-ouvertes.fr/hal-00798734/file/jcli-d-11-00049_2E1.pdf; https://doi.org/10.1175/JCLI-D-11-00049.1

International audience A dynamical model is constructed of the northern summertime global circulation, maintained by empirically derived forcing, based on the same dynamical code that has recently been used to study African easterly waves (AEWs) as convectively triggered perturbations (Thorncroft et al.; Leroux and Hall). In the configuration used here, the model faithfully simulates the observed mean distributions of jets and transient disturbances, and explicitly represents the interactions between them. This simple GCM is used to investigate the origin and intraseasonal intermittency of AEWs in an artificially dry (no convection) context. A long integration of the model produces a summertime climatology that includes a realistic African easterly jet and westward-propagating 3-5-day disturbances over West Africa. These simulated waves display intraseasonal intermittency as the observed AEWs also do. Further experiments designed to discern the source of this intermittency in the model show that the simulated waves are mainly triggered by dynamical precursors coming from the North Atlantic storm track. The model is at least as sensitive to this remote influence as it is to local triggering by convective heating.