Institute of Geophysics, University of Tehran, P.O. Box 14155-6466, Tehran, Iran
In mid-latitudes, the surface cyclones and anticyclones are mainly generated by the action of mid to upper tropospheric baroclinic waves. To understand the mechanisms of formation and intensification of these weather systems, the study of baroclinic wave packets is essential. In the first part of this two-part paper, using the global data from NOAA for Feb. 2003 provided by Iran Meteorological Organization, a synoptic-dynamic study to detect baroclinic wave packets and determine their evolution is undertaken. Hovmoller diagrams and complex demodulation as applied to various dynamical quantities have been used to detect wave packets and determine their characteristics. For the upper tropospheric wave packets detected in Hovmoller diagrams, group velocity is greater than the phase speed. This characteristic of wave packets is consistent with downstream development of the waves. The results indicate that the blocking action in the east of the Pacific and Atlantic Oceans in the first 10 days of Feb. inhibits the presence of baroclinic wave packets and their related low-level activities.
The wave packets detected by Hovmoller and complex demodulation methods have been compared. For the period 10th to 15th of Feb. the two methods consistently give the same packets. Tracking the wave packets by using complex demodulation point to the intensification and weakening of the waves over, respectively, the west and east of the Pacific and Atlantic Oceans, which is studied in more detail in the second part by dynamical analysis considering the energetics of the waves.