Flare response to the thermospheric diurnal neutral wind measured by the OMTIs’ Fabry-Perot Interferometers
Abstract:This research aims at investigating the influence of flare events to the thermospheric tidal wind in order to grasp the EUV effect of the solar activity to upper atmospheric circulation. The neutral wind at about 250km level observed with the 630nm airglow by Fabry-Perot interferometers of the Optical Mesosphere Thermosphere Imagers (OMTIs) is analyzed. We used the 15-minutes interval data at Shigaraki for the year 2000 to 2013. 10953 of 59881 samples became usable after a quality control.
We used the flare list issued by NOAA extracted from the X-rays from GOES satellites. There are 131 of X-class flares and 1510 of M-class flares during the 14 years. However, the number of samples to which effective observation of FPI is carried out at the flare peak time was 51.
Before composite of the wind at the time of solar flare (so-called superimposed epoc analysis), monthly climatological wind is made. First, the valid data of every month were averaged in every 15 minutes for 9-21 UTC, then, three months data were averaged. Further, the 15-minutes temporal variation data was smoothed with a Gaussian filter.
From the 51 sample data containing the flare peak time, the zonal wind (Ve) and the meridional wind (Vn) were composed after deducted the above mentioned climatology with a flare peak time as the starting point (t=0). Supposing the atmosphere on the daytime side expands under the influence of the flare temporarily and the advection current to the night side is strengthened, the eastward (westward) wind should be strengthened before (after) midnight. Since the influence of the increment of the air expansion in mid-night may have been offset, the samples which flare occurs before midnight (39 samples) were composited.
As a result, as for Ve, significant change of eastward wind to westward wind compared to the standard deviation is observed after 3hrs and a half after solar flare occurred, while as for Vn, significant enhancement of southward component is observed after 4 hrs of the flares. Although some increments are observed after the flare to the above mentioned change for both Vn and Ve, signals are not clear. Further analysis by using other station data and other instruments are required for examination of the significance.
This research was done as part of Inter-university Upper atmosphere Global Observation NETwork (IUGONET).