Some aspects of tropospheric circulation during midwinter stratospheric warming events

Investigation of planetary-scale pressure fields in mid-troposphere before, during, and after the occurrence of four midwinter polar stratospheric warmings has been made. Similar investigation has been made in four winters during which no such warming occurred. Wide-spread high-latitude height rises of the 500-mb surface were found during the course of the warming. Winters without such stratospheric events were not always free of such height increases at high latitudes, but these were restricted to narrow longitude bands and did not persist through the period of interest. Zonal kinetic energies from 40°N to 80°N at 500 mb were calculated. In winters when warming events occurred, the stratospheric meridional temperature gradient reversed sense in early February. At that time, consistently less mid-tropospheric zonal kinetic energy was present than in winters when no stratospheric warming occurred. Before the onset of the period when stratospheric warmings tend to occur, the parameter distinguishing the two sets of winters was the phase velocity of wave number 1 in high latitudes. During the initial phases of the warmings, the movement of this wave number changed from an eastward to a westward direction in all four winters. The results, although solely statistical, suggest that the troposphere is participating in the energetics of the stratospheric warmings.