סמינר בחוג לגיאופיזיקה: A dynamical perspective on the atmospheric temperature variability and its response to climate change

Abstract:

Earth's atmospheric temperature distribution is often described by its mean, which is directly related to the climatological state, and by its variance, which is influenced by short timescale changes such as passing weather systems. Higher order terms describing the temperature variability, such as skewness, often receive less attention. The skewness is a measure of the asymmetry between the positive and negative tails of the distribution, and is therefore closely related to extreme events like heat waves or cold spells. The spatial distribution of the temperature skewness has important consequences for weather and climate. It was recently suggested that the positive (negative) skewness of temperature on the poleward (equatorward) flank of the jet may be a result of horizontal advection by cyclone and anticyclone pairs. Here we take a dynamical Lagrangian tracking approach to further study what controls the spatial structure of the temperature distribution. We isolate warm and cold low-level temperature anomalies in reanalysis data and employ a feature-tracking algorithm to investigate their formation, intensity, and motion. We show that warm (cold) anomalies are generated on the equatorward (poleward) side of the storm tracks, and maximize on the poleward (equatorward) side. An investigation of the composite thermodynamic budget shows that while the temperature anomaly grows mainly through the linear meridional advection term (as in linear baroclinic instability), it is the nonlinear meridional advection that is responsible for the poleward (equatorward) motion of the warm (cold) anomalies, and therefore to the differential skewness. The tracking approach gives insights into the distinct contributions of warm and cold anomalies to the Eulerian diagnostics of temperature variance and skewness, and is especially useful when considering potential changes under a global warming scenario. For example, we find that over central Europe, while temperature variance is expected to increase in summer, it is actually the cold anomalies that contribute to the increase in variability. On the contrary, in winter, it is the warm anomalies that intensify relative to the mew climate. In the SH, the poleward shift and increase of the temperature variance is shown to be composed of a poleward shift in the genesis (lysis) of warm (cold) anomalies, and an increase in their intensities on the poleward (equatorward) side. These changes in skewness and variance might have a large influence on agriculture, animals as well as humans, as they adapt to new mean climate state but also experience new relative changes. 

מארגן הסמינר: פרופ' איל חפץ