5:15 PM - 7:15 PM
[PEM12-P13] Statistical study of latitudinal dependence of medium-scale traveling ionospheric disturbance : GPS observation in Japan
Keywords:MSTID, Ionosphere, GPS
In order to elucidate latitudinal dependence of Medium-Scale Traveling Ionospheric Disturbance(MSTIDs), we analyzed Total Electron Content(TEC) data obtained from GPS receiver network in Japan during 19 years from 2000 to 2019. We have calculated the detrended TEC by subtracting the 1-h running average from the original TEC data for each satellite and receiver pair, and made two-dimensional maps of the detrended TEC with a spatial resolution of 0.15°×0.15°in longitude and latitude. We have investigated MSTID activity, defined as δI/I ,where δI is a standard deviation of the detrended TEC within the area of 4.05°×4.05° in longitude and latitude, and I is the average vertical TEC in the same area. We have calculated auto-correlation function of the detrended TEC from each 2-h time series of the detrended TEC to estimate the horizontal propagation velocity and direction of MSTIDs.
We investigated seasonal variation of MSTID activity, and propagation direction and velocity of MSTID from 2000 to 2019 at four locations, Hokkaido, Tohoku, Kinki, and Kyushu. At all four locations, MSTID activity during nighttime shows semiannual variation, with a first peak in summer and second peak in winter, and MSTID activity during daytime is high in winter. Propagation direction was southwest in all observation points. On average, MSTID at the four locations propagate southwestward during nighttime and southward during daytime. These features are consistent with previous studies and support the idea that daytime MSTID could be caused by gravity waves, and that nighttime MSTID could be caused by the Perkins instability.
We investigated year to year variation of MSTID activity, and propagation direction and velocity of MSTID during daytime from 2000 to 2019 at four locations. Latitudinal dependence of propagation direction is not discernible. This feature can be interpreted as follows. The daytime MSTIDs originate from atmospheric gravity waves. When the atmospheric gravity waves propagate equatorward, the neutral atmosphere oscillates in the direction parallel to the geomagnetic field lines, perturbations in the electron density become most prominent, making MSTIDs more easily observable. On the other hand, the propagation velocity of the daytime MSTIDs exhibits noticeable latitude-dependence during the high solar activity period. Under the high solar activity conditions, the average daytime propagation velocity is 105m/s, 101m/s, 82m/s, and 80m/s in Hokkaido, Tohoku, Kinki, and Kyushu, respectively. The propagation velocity ranges from 50~170m/s in Hokkaido, and 30~160m/s in Kyushu. This result can be explained by the higher viscosity of the neutral atmosphere at higher latitudes, where the atmosphere density is lower. Consequently, gravity waves with shorter vertical wavelengths are more likely to dissipate, leading to a lack of MSTIDs with low propagation velocities at higher latitudes.
We investigated seasonal variation of MSTID activity, and propagation direction and velocity of MSTID from 2000 to 2019 at four locations, Hokkaido, Tohoku, Kinki, and Kyushu. At all four locations, MSTID activity during nighttime shows semiannual variation, with a first peak in summer and second peak in winter, and MSTID activity during daytime is high in winter. Propagation direction was southwest in all observation points. On average, MSTID at the four locations propagate southwestward during nighttime and southward during daytime. These features are consistent with previous studies and support the idea that daytime MSTID could be caused by gravity waves, and that nighttime MSTID could be caused by the Perkins instability.
We investigated year to year variation of MSTID activity, and propagation direction and velocity of MSTID during daytime from 2000 to 2019 at four locations. Latitudinal dependence of propagation direction is not discernible. This feature can be interpreted as follows. The daytime MSTIDs originate from atmospheric gravity waves. When the atmospheric gravity waves propagate equatorward, the neutral atmosphere oscillates in the direction parallel to the geomagnetic field lines, perturbations in the electron density become most prominent, making MSTIDs more easily observable. On the other hand, the propagation velocity of the daytime MSTIDs exhibits noticeable latitude-dependence during the high solar activity period. Under the high solar activity conditions, the average daytime propagation velocity is 105m/s, 101m/s, 82m/s, and 80m/s in Hokkaido, Tohoku, Kinki, and Kyushu, respectively. The propagation velocity ranges from 50~170m/s in Hokkaido, and 30~160m/s in Kyushu. This result can be explained by the higher viscosity of the neutral atmosphere at higher latitudes, where the atmosphere density is lower. Consequently, gravity waves with shorter vertical wavelengths are more likely to dissipate, leading to a lack of MSTIDs with low propagation velocities at higher latitudes.