عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Climatological study of the mid-latitude storm tracks was investigated using the daily Global Forecast System (GFS) and the National Centers for Environmental Prediction (NCEP) Reanalysis data sets from 1948 to 2008 winter seasons. In anomalous winter 2007-2008, decreasing of eddy kinetic energy along with the reduction of eddy available potential energy upstream of Atlantic storm track are related to weakening of the baroclinic generation with respect to the long-term means. In addition to the baroclinic conversion, the most important term in strengthening and stretching of the jet-stream upstream of Atlantic storm track, the increase of the positive values of barotropic conversion plays a controlling role.
Study of the energetics over the Middle East shows that in January 2008, the domination of the subtropical jet stream core over the south-western Iran was responsible for the increase of the mean kinetic energy. Baroclinic generation had a remarkable role in energy feeding from downstream of Mediterranean, which produced strong convergence of ageostrophic flux due to the downstream development over the Mediterranean storm track. Significant increase of baroclinic conversion, baroclinic generation, and divergence of ageostrophic flux have their maximum values over the north of Arabian Peninsula causing intense eastward radiation of eddy energy toward the central part of Iran. In this month, the maximum convergence of ageostrophic flux shows that on average, Iran was a strong sink of energy associated with deepening of thermal trough and dominance of unprecedented cold anomalies over the northern Iran in the recent decades.
In February 2008, in addition to the increase of the mean kinetic energy due to the downstream displacement of subtropical jet-stream over south-western Iran, the maximum of positive barotropic conversion anomaly in Northern Hemisphere was located over this region. Local core of baroclinic generation over the central part of Iran elongated between the significant positive bands of barotropic conversion was accompanied by the increase of the eddy kinetic energy and eddy available potential energy, respectively. This indicates that Iran, on average, was a transmitter of energy toward the adjacent eastern regions during this month.