We proposed to use the Arecibo incoherent scatter radar and COSMIC-GPS datasets to gain significant new understanding of where and how planetary scale wave in the atmosphere drive variability in the ionosphere. With the support of this grant, we observed an ultra-fast Kelvin wave (UFKW) in the mesosphere (~ 60-90 km). This UFKW is seen to propagate directly to ~105 km altitude. The UFKW is identified in a variety of observations, both from the ground and space, including the first ever observations by an incoherent scatter radar. Non-linear interaction between the UFKW and the diurnal tide is seen with the ground based meteor radar at Thumba and the incoherent scatter radar at Arecibo, Puerto Rico.

Atmospheric waves and their interactions in the middle thermosphere (~300 km) are studied based on Arecibo incoherent scatter radar observations between 1988 and 1993.  Strong interactions between the diurnal tide (having a period of 24 hours) and gravity waves (typically having a period less than a few hours) are frequently observed. These strong interactions can persist for several days, although they are highly intermittent. Moreover, the sum and difference interactions between the diurnal tide and gravity waves always occur simultaneously and the energy exchange between the interacting waves is sometimes reversible.  A combination of bispectral and correlation analyses verifies the occurrence of nonlinear interactions among different tidal components in the middle thermosphere. Our study provides proof of strong tide–gravity wave, tide–planetary wave, and tide–tide interactions in the middle thermosphere, which has rarely been reported to date.

The high density region of the ionosphere above Arecibo is often observed to drop substantially around midnight. This phenomenon is called midnight collapse. In our study for midnight collapse, we find that both electric field and meridional wind play an important role in driving the ionosphere downward. For the meridional wind, we identified the terdiurnal tide (having a period of 8 hours) being the most important tidal component. Preconditioning of the ionosphere prior to collapse is essential for large drops of the ionosphere.

Trace metal layers exist in the mesosphere and lower thermosphere (in the altitude range of 80 to 110 km) due to meteoric ablations. We have carried out a comparative study of the mesospheric Na and Fe layers by using simultaneous and common volume lidar measurements made at the Arecibo Observatory. The temporal variations of the two species are highly correlated at practically all heights, although not always positively. Positive correlations occur in the bottom and top sides while negative correlation is observed in a relatively narrow region in the middle part. The observed region of negative correlation appears to be slightly lower than that of the expected region of negative correlation based on inert response to dynamics. It appears that such a difference is due to temperature-dependent chemistries. 

With the support of this grant, four archival journal papers have been published and one additional paper is under review. Results obtained under this grant were also presented at several conferences. The project also involved collaborations with scientists from other countries. 

Last Modified: 05/29/2014
Modified by: Qihou Zhou