Circumglobal teleconnections and wave packets associated with Israeli winter precipitation

This investigation performs diagnostic analyses with NCEP/NCAR reanalysis data and Israeli precipitation data to examine the dynamical processes that drive the teleconnection pattern associated with Israeli winter precipitation anomalies. A dipole teleconnection pattern with one centre of action over western Europe and another centre of action over the eastern Mediterranean (EM) is found to be associated with the winter precipitation anomalies in Israel. This pattern is referred to as the southern Levant (SL) pattern. The positive (negative) phase of the SL pattern is found to be closely associated with enhanced (reduced) precipitation in Israel. Composites of the 300 hPa stream-function field show that both phases of the SL pattern are associated with eastward propagating wave packets that traverse about three-quarters of the distance across the globe. These wave packets, which have a phase speed that is close to zero, originate over the northeast Pacific (the east coast of North America) for the positive (negative) SL phase, and propagate eastward across the North Atlantic, western Europe, the EM, and southern Asia, until they eventually decay over the northwest Pacific. As these wave packets pass over western Europe and the EM, the SL pattern is triggered and anomalies in Israeli winter precipitation occur. The SL pattern is found to have an e-folding time-scale of 4 days, which is determined by the group velocity of the wave packet. The time-averaged spatial structure of the circumglobal wave packet closely resembles the first empirical orthogonal function of the hemispheric 300 hPa meridional wind field. This suggests that the circumglobal wave packet may be a fundamental pattern of variability which is relevant for the entire Northern Hemisphere.