5:15 PM - 6:45 PM
[PEM12-P15] Statistical Analysis of the Coupling Process between Medium-Scale Traveling Ionospheric Disturbance and Sporadic E-layer Based on GPS and Ionosonde Observations
Keywords:TEC, MSTID, Ionosonde, Sporadic E-layer, Solar activity, Perkins instability
Previous studies have suggested that the E and F regions are coupled by electrodynamic forces. In this study, to study activity and latitudinal dependence of the coupling between the sporadic E (Es) layer and Medium-Scale Traveling Ionospheric Disturbances (MSTID) in the F region, ionosonde data obtained at Wakkanai, Kokubunji, Yamagawa, and Okinawa and Total Electron Content (TEC) data obtained from the Global Positioning System (GPS) receivers in Japan between May and August from 1997 to 2022 were examined.
The perturbation components of TEC due to MSTIDs were obtained by subtracting a one-hour moving average from the original TEC data for each pair of satellite and receiver. MSTID activity was defined as a ratio of (dI/I) ×100%, where dI: the standard deviation of TEC perturbations observed in specific regions ranging 4.05°×4.05° over each ionosonde in one hour, and I is the background TEC observed in the same region and during the same period as dI.
MSTID activity and two Es layer parameters (foEs, dfo-b(≡foEs-fbEs)) are averaged between 19-02 LT (foEs: critical frequency of the Es layer, fbEs: blanket frequency of the Es layer). dfo-b is considered to indicate inhomogeneity in the electron density of the Es layer. The cross-correlation coefficients between the daily variations of MSTID activity and the two Es layer parameters from May to August were calculated. To investigate the mechanism of electric field generation in the F-region, daily nightly averages of foEs, dfo-b, and foF2 (critical frequency of the F region) from May to August were averaged yearly. The cross-correlation coefficients between MSTID activity and foEs(dfo-b) were positive (0.2-0.8) for all three sites except Okinawa, and tends to increase with latitudes. The foEs (dfo-b) does not show distinct difference among sites, but foF2 values increases with latitude. According to this latitudinal variation of the E and F region electron density, we can speculate that the electric field generation in the Es layer could play more important role at higher latitudes. This could be a reason why the correlations between daily variations of MSTID activity and foEs and between daily variations of MSTID and dfo-b increases with latitude.
The cross-correlation coefficients between MSTID activity and foEs(dfo-b) for each year were compared with F10.7. The cross-correlation coefficients between MSTID activity and foEs (dfo-b) were positively correlated with solar activity at Wakkanai and Kokubunji. The solar activity dependence of the cross-correlation coefficient between MSTID activity and foEs(dfo-b) is more pronounced at higher latitudes. This latitudinal dependence could be interpreted as below. [The growth rate of Perkins instability is inversely proportional to plasma density-weighted field-line integrated ion-neutral collision frequency. Under high solar activity, the density of the neutral atmosphere is larger, the collision frequency is also larger, and thus, the growth rate of Perkins instability is smaller. Therefore, the contribution of the electric field generation by the Es layer instability to the growth of MSTIDs during high solar activity periods is likely to have a larger effect..
In the above, the cross-correlation between nightly averaged MSTID activity and foEs(dfo-b) was examined, and hourly cross-correlation between MSTID activity and foEs (dfo-b) was also examined. The results showed that the correlation between MSTID activity and foEs(dfo-b) was larger than 0.4 for all time periods (19-02 LT) when MSTIDs appeared. This suggests that the MSTID and Es layer are always coupled during the nighttime MSTID appearance.
The perturbation components of TEC due to MSTIDs were obtained by subtracting a one-hour moving average from the original TEC data for each pair of satellite and receiver. MSTID activity was defined as a ratio of (dI/I) ×100%, where dI: the standard deviation of TEC perturbations observed in specific regions ranging 4.05°×4.05° over each ionosonde in one hour, and I is the background TEC observed in the same region and during the same period as dI.
MSTID activity and two Es layer parameters (foEs, dfo-b(≡foEs-fbEs)) are averaged between 19-02 LT (foEs: critical frequency of the Es layer, fbEs: blanket frequency of the Es layer). dfo-b is considered to indicate inhomogeneity in the electron density of the Es layer. The cross-correlation coefficients between the daily variations of MSTID activity and the two Es layer parameters from May to August were calculated. To investigate the mechanism of electric field generation in the F-region, daily nightly averages of foEs, dfo-b, and foF2 (critical frequency of the F region) from May to August were averaged yearly. The cross-correlation coefficients between MSTID activity and foEs(dfo-b) were positive (0.2-0.8) for all three sites except Okinawa, and tends to increase with latitudes. The foEs (dfo-b) does not show distinct difference among sites, but foF2 values increases with latitude. According to this latitudinal variation of the E and F region electron density, we can speculate that the electric field generation in the Es layer could play more important role at higher latitudes. This could be a reason why the correlations between daily variations of MSTID activity and foEs and between daily variations of MSTID and dfo-b increases with latitude.
The cross-correlation coefficients between MSTID activity and foEs(dfo-b) for each year were compared with F10.7. The cross-correlation coefficients between MSTID activity and foEs (dfo-b) were positively correlated with solar activity at Wakkanai and Kokubunji. The solar activity dependence of the cross-correlation coefficient between MSTID activity and foEs(dfo-b) is more pronounced at higher latitudes. This latitudinal dependence could be interpreted as below. [The growth rate of Perkins instability is inversely proportional to plasma density-weighted field-line integrated ion-neutral collision frequency. Under high solar activity, the density of the neutral atmosphere is larger, the collision frequency is also larger, and thus, the growth rate of Perkins instability is smaller. Therefore, the contribution of the electric field generation by the Es layer instability to the growth of MSTIDs during high solar activity periods is likely to have a larger effect..
In the above, the cross-correlation between nightly averaged MSTID activity and foEs(dfo-b) was examined, and hourly cross-correlation between MSTID activity and foEs (dfo-b) was also examined. The results showed that the correlation between MSTID activity and foEs(dfo-b) was larger than 0.4 for all time periods (19-02 LT) when MSTIDs appeared. This suggests that the MSTID and Es layer are always coupled during the nighttime MSTID appearance.