Statistical height‐dependent relative importance of the Lorentz force and Joule heating in generating atmospheric gravity waves in the auroral electrojets

Abstract

On the basis of 28 days of European Incoherent Scatter Common Program 1 mode data obtained between 1989 and 1991, we have determined statistical ratios of the Lorentz force (L) to the Joule heating rate terms (J) in generating atmospheric gravity waves in the auroral electrojets between 101 and 125 km altitudes. Under the altitude of 120 km the ratio (L/J) rapidly decreases with increasing height, indicating that the relative importance of the two sources is very critically dependent on altitude. Above this altitude, L/J is approximately constant with height. We have also derived a transition height of about 116 km. Under this height the Lorentz force is relatively important. Above this height, Joule heating dominates. Considering the effect of the neutral wind, relative deviations caused by the neutral wind are estimated at less than 10% between 101 and 125 km altitudes. Therefore we can ignore the effect of neutral wind on the ratio. In order to fulfill the demand, in practice, a statistical curve of the ratio with height has been provided.

Effects of TADs on the F region of the mid-latitude ionosphere during an intense geomagnetic storm

“…The auroral electrojet is a very important candidate for explaining the generation of such large scaled TADs (Yeh and Liu, 1974;Jing and Hunsucker, 1993;Prö lss and Roemer, 2000;Yuan et al, 2005). With observations of above two ionosondes, the start to the enhancement of the F1 cusp at Wuhan lags that at Kokubunji by 15 min, same as time delay of the increase of foF2 between those two stations.…”

“…In our case, on the contrary, we observe a short-duration positive ionospheric storm caused by the equatorial meridional wind associated with TADs mentioned above. Since the equatorward meridional wind velocity and associated upward drift velocity increase with height (Bauske and Prö lss 1997;Yuan et al, 2003), they may cause a deeper and wider F1/F2 valley. As a result, the pre-existing F1 cusp becomes better developed in the F1 region.…”

“…Imaging of a TAD structure using TEC data is a powerful technique to quantify the existence of TADs and their propagation velocity (e.g., Shiokawa et al, 2002Shiokawa et al, , 2003Nicolls et al, 2004). For the study of ionospheric storms, many authors have focused on the F2 layer storm effects (e.g., Buonsanto, 1999;Lee et al, 2002;Yuan et al, 2003), because F1 layer storm effects are relatively small compared to the F2 layer ones. Recently, some authors have preformed morphological studies of geomagnetic storm effects at F1 layer heights (Buresova andLastovicka, 2001, Buresova et al, 2002;Mikhailov and Schlegel, 2003).…”

Radar observations of simultaneous traveling ionospheric disturbances and atmospheric gravity waves

“…Thus, even storm activity must be excluded as a possible source. The other possible sources are the terminator [Forbes et al, 2008], where AGWs are generated by solar heating, and the energy input in the upper atmosphere by auroral effects [Yuan et al, 2005].…”

“…The sources of AGWs may lie in the troposphere but also at thermospheric heights. The important sources in the high‐latitude thermosphere include various types of auroral inputs, i.e., particle precipitation, Joule heating, and Lorentz forcing [ Yuan et al , ]. Another possible source is the terminator, where air entering from shadow to sunlight or from sunlight to shadow experiences expansions or contractions [ Galushko et al , ; Forbes et al , ; Afraimovich , ].…”