Stratospheric Circulation Response To A Solar Eclipse

The new knowledge gained from Meteorological Rocket Network systems that the stratospheric circulation responds to diurnally impressed solar heating with a temperature variation of approximately 15C and a wind variation of approximately 30 meters per second peak to peak at the stratopause has led to greater interest in other sources of perturbation in this upper atmospheric region. A solar eclipse exhibits physical input characteristics which are sufficiently different from diurnal variations in space and time scales to make its analysis of value in establishing the overall response characteristics of the stratospheric circulation. Employing certain assumptions and using the available data on diurnal variations, a model of the stratospheric temperature and circulation structure associated with an eclipse shadow has evolved. In particular, this model was designed to represent the situation which will occur in the morning hours over Tartagal, Argentina, on 12 November 1966. The results of this study indicate that the diurnal temperature variation will be locally reduced by approximately 4 degrees Celsius along the totality path and that a local circulation system of several thousand kilometers diameter will be set up around the path of the lunar shadow with peak winds of the order of several meters per second. Such a perturbation in the stratospheric circulation can probably be observed with only relatively minor adjustments to available meteorological rocket systems. (Author).

(cont.) The negative phase of the annular mode can continue as long as both the lower stratospheric winds remain weak and the wave source is sufficient. Model runs with lower stratospheric winds that were always sufficiently weak or always too strong showed no significant tropospheric response to any extreme stratospheric events. Similarly, shifting mountains into the polar region appeared to shift the wave drag away from synoptic eddy feedback region. In either of these two cases, none of the model runs exhibited signs of a tropospheric response, consistent with the wave drag projection onto the annular mode having a key role in allowing the stratosphere to affect the tropospheric circulation.

Analysis of stratospheric soundings obtained during the first four years of the meteorological rocket network's exploration has provided new insight into the dynamics of stratospheric circulation. The data indicate that the winter storm period from mid-December to mid-February results from interaction between the opposing circulations of the winter and summer hemispheres. Initation of these disturbances occurs in low latitudes of the winter hemishpere when the summer hemisphere circulation reaches its peak and actively invades the winter hemisphere. These disturbances propagate only toward the winter pole and act as an effective brake on the development of the winter westerly circulation. Except for this very pronounced period of dynamic interchanges the stratosphere is found to respond systematically to changes in solar heat input. (Author).

The atmosphere's response to the total solar eclipse of 4 December 2002 is studied using a prototype high-altitude global numerical weather prediction model (NOGAPS-ALPHA).