Isolation of the global MLT thermal response to recurrent geomagnetic activity

Abstract

Recurrent geomagnetic activity at multi‐day periodicities (near 5.5, 7 and 9 day subharmonics of solar rotation) have been associated with high speed solar wind stream variations and have recently been shown to induce congruent multi‐day periodic responses in the global upper atmosphere. The ability to relate these periodicities in geomagnetic activity to global temperature observations from the TIMED/SABER instrument enables isolation of the global thermal response in the lower thermosphere and mesosphere due to geomagnetic activity. Observations from the TIMED/SABER instrument at altitudes below 120 km clearly show a zonally symmetric (s = 0) modulation in the global temperature field at a 9‐day period known to result from recurrent geomagnetic activity forced by corotating interaction regions (CIRs). The temporal variation of this zonally symmetric 9‐day perturbation in temperature is strongly correlated to the 9‐day variations in the Kp geomagnetic activity index in 2005, with the most significant correlation occurring above 110 km and polewards of 40° latitude in both hemispheres. The temperature amplitude at the 9 day period is in excess of 10 K above 110 km and increasing in amplitude poleward of 40°. The phase of the temperature maximum associated with such disturbances is coherent with altitude and hemisphere, with the disturbance occurring first near 110 km and then peaking at altitudes above and below this region hours later.