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Center for Nonlinear Studies |
The Intra-Americas Sea (IAS) dynamics have been studied mainly for the summer and winter season. In contrast, the spring conditions have been studied less. Here we analyze the boreal spring variability of the IAS ocean-atmosphere interactions, the IAS low-level jet (IA-LLJ) and the relation with precipitation and tornadic activity in the region of the lower Mississippi, Tennessee and Ohio river basins (MORB). The main mode of variability of the spring IA-LLJ is obtained from the combined empirical orthogonal function (EOF) of the zonal and meridional winds at 925-hPa. The first mode of variability of the IA-LLJ is related mainly to the Pacific North American (PNA) pattern and to an increase in precipitation over the eastern half of North America as the moisture fluxes associated with the IA-LLJ increase. Tornadic activity in nine states spanning the MORB region is also significantly correlated with the PNA index and the Pacific Decadal Oscillation (PDO) index in March. Among the environmental factors that influence tornadic activity are a southwesterly wind shear, dry transients at the mid-troposphere, moist transients at low levels, and an increase in convective available potential energy (CAPE). Based on statistical analysis we observe that teleconnections originating in the midlatitude Pacific affect mostly the Gulf of Mexico, whereas teleconnections from the tropical Pacific affect mostly the Caribbean Sea. Furthermore, the Pacific teleconnections that influence the IAS sea surface temperatures (SST) do so affecting the Gulf of Mexico in an opposite manner to the Caribbean Sea. By calculating an index that represents an IAS SST anomaly dipole we find that the dipole forms mostly in response to changes in the air-sea heat fluxes. Changes in shortwave radiation arise, in part, by the cloudiness triggered by the air-sea differences in humidity, and also by the changes in the convection cell that connects the Amazon basin to the IAS. Weaker Amazon convection (e.g., in the event of a warm ENSO event) reduces the subsidence over the IAS and henceforth the IAS cloudiness increases (and the shortwave radiation decreases). These studies contribute to a greater understanding of how the IAS is influenced by different Pacific and Atlantic teleconnections during boreal spring. * Based on work done at the NOAA Atlantic Oceanographic and Meteorological Laboratory (AOML) and the Cooperative Institute for Marine and Atmospheric Studies (CIMAS) in collaboration with Dr. David Enfield and Dr. Chunzai Wang.
Host: Wilbert Weijer