ORCID Profile
0000-0002-5840-2120
Current Organisation
Karlsruher Institut für Technologie
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Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-7263
Abstract: & & & span& The El Ni& #241 o Southern Oscillation (ENSO) is typically associated with below-average rainfall in the winter-spring season in southeastern Australia. However, there is also a large case-to-case variability pointing to the non-linear relationship of El Ni& #241 o strength and the impact on east Australian rainfall. Despite recent progress in understanding the linkage of remote climate drivers and this variability, the dynamical processes by which the drivers transmit their influence on rainfall are not fully understood. With this study, we aim to advance the dynamical understanding by relating patterns of monthly rainfall anomalies over southeastern Australia to a novel dataset of objectively identified weather systems derived from ERA-Interim reanalyses. & /span& & & & & & span& We find 4 rainfall anomaly patterns in the austral winter-spring season (JJASON) with above-average rainfall (Cluster 1), below-average rainfall (Cluster 2), above-average rainfall limited to the East Coast (Cluster 3) and above-average rainfall limited to the South Coast (Cluster 4) in southeastern Australia. & /span& & span& Changes in the frequency of weather systems explain partly the rainfall anomalies in the clusters. Results indicate a significant increase of weather system activity in Cluster 1 and a weakening of weather system activity in Cluster 2. In Cluster 3, enhanced blocking favors the development of cut-off lows on & /span& & span& its& /span& & span& northeastern flank leading to increased rainfall along the East Coast. Positive rainfall anomalies along the South Coast are associated with frontal rainfall due to an equatorward shift of the midlatitude storm track (Cluster 4). & /span& & span& Most of the rainfall is produced by warm conveyor belts and cut-off lows but the contributions strongly vary between the clusters. We further find that anomalies in rainfall result from changes in rainfall frequency more than in rainfall intensity. By calculating backward trajectories of warm conveyor belt and cut-off low rainfall, we point to the importance of moist air masses from the Coral Sea and the northwest coast of Australia for wet months. Air parcels, that end up in WCB or cut-off low rainfall, reach southeastern Australia from the dry remote areas to the north and not as one would expect from the Southern Ocean. & /span& & &
Publisher: Wiley
Date: 07-2022
DOI: 10.1002/QJ.4338
Abstract: Equatorial waves (EWs) are synoptic‐ to planetary‐scale propagating disturbances at low latitudes with periods from a few days to several weeks. Here, this term includes Kelvin waves, equatorial Rossby waves, mixed Rossby–gravity waves, and inertio‐gravity waves, which are well described by linear wave theory, but it also other tropical disturbances such as easterly waves and the intraseasonal Madden–Julian Oscillation with more complex dynamics. EWs can couple with deep convection, leading to a substantial modulation of clouds and rainfall. EWs are amongst the dynamic features of the troposphere with the longest intrinsic predictability, and models are beginning to forecast them with an exploitable level of skill. Most of the methods developed to identify and objectively isolate EWs in observations and model fields rely on (or at least refer to) the adiabatic, frictionless linearized primitive equations on the sphere or the shallow‐water system on the equatorial ‐plane. Common ingredients to these methods are zonal wave‐number–frequency filtering (Fourier or wavelet) and/or projections onto predefined empirical or theoretical dynamical patterns. This paper gives an overview of six different methods to isolate EWs and their structures, discusses the underlying assumptions, evaluates the applicability to different problems, and provides a systematic comparison based on a case study (February 20–May 20, 2009) and a climatological analysis (2001–2018). In addition, the influence of different input fields (e.g., winds, geopotential, outgoing long‐wave radiation, rainfall) is investigated. Based on the results, we generally recommend employing a combination of wave‐number–frequency filtering and spatial‐projection methods (and of different input fields) to check for robustness of the identified signal. In cases of disagreement, one needs to carefully investigate which assumptions made for the in idual methods are most probably not fulfilled. This will help in choosing an approach optimally suited to a given problem at hand and avoid misinterpretation of the results.
Publisher: Wiley
Date: 2011
DOI: 10.1002/ASL.335
Publisher: American Meteorological Society
Date: 08-2012
Abstract: The representation of tropical convection remains a serious challenge to the skillfulness of our weather and climate prediction systems. To address this challenge, the World Climate Research Programme (WCRP) and The Observing System Research and Predictability Experiment (THORPEX) of the World Weather Research Programme (WWRP) are conducting a joint research activity consisting of a focus period approach along with an integrated research framework tailored to exploit the vast amounts of existing observations, expanding computational resources, and the development of new, high-resolution modeling frameworks. The objective of the Year of Tropical Convection (YOTC) is to use these constructs to advance the characterization, modeling, parameterization, and prediction of multiscale tropical convection, including relevant two-way interactions between tropical and extratropical systems. This article highlights the erse array of scientifically interesting and socially important weather and climate events associated with the WCRP–WWRP/THORPEX YOTC period of interest: May 2008–April 2010. Notable during this 2-yr period was the change from cool to warm El Niño– Southern Oscillation (ENSO) states and the associated modulation of a wide range of smaller time- and space-scale tropical convection features. This period included a near-record-setting wet North American monsoon in 2008 and a very severe monsoon drought in India in 2009. There was also a plethora of tropical wave activity, including easterly waves, the Madden–Julian oscillation, and convectively coupled equatorial wave interactions. Numerous cases of high-impact rainfall events occurred along with notable features in the tropical cyclone record. The intent of this article is to highlight these features and phenomena, and in turn promote their interrogation via theory, observations, and models in concert with the YOTC program so that improved understanding and pre- dictions of tropical convection can be afforded.
Publisher: Wiley
Date: 17-05-2020
DOI: 10.1002/QJ.3808
No related grants have been discovered for Andreas H. Fink.