AWL
Geomagnetic storms can disrupt social infrastructure on Earth; thus, accurate and timely monitoring is required to reduce their future socioeconomic impact. This study compares the planetary geomagnetic disturbance index (KP) with local indices at Fredericksburg (FRD) and Kakioka (KAK) stations. Local K indices at KAK and Cheongyang (CYG) are estimated and validated using indices observed at both stations. We found generally similar correlations between the KP index and the local K indices at FRD and KAK; however, their details differ. The results show that, even when planetary geomagnetic storms are observed, the local K can be smaller than the observed KP. This implies that both KP and local K should be simultaneously monitored. Real-time estimation of local K shows that the estimated K at KAK and CYG correlates well with the observed K. The estimation probability at KAK and CYG, with an error range of ±1, is greater than 98% when the local K is greater than 3. This suggests that the estimation approach used in this study can be operationally applied for timely monitoring of local geomagnetic disturbances.
We analyzed plasma scale height observations (about 80 km altitude) over the Eifel region (50°N, 6°E) observed from Kühlungsborn (54°N, 12°E) in the time interval 1959–2016 and OH* temperatures (center altitude 87 km) observed from Wuppertal (51°N, 7°E) in the time interval 1988–2016. In summer months both time series show a dominant oscillation with a period of about two decades (20–26 years) with amplitudes of about 180 m and 3 K, respectively. These two oscillations are anticorrelated, because their observation altitudes are located above and below the temperature minimum in the mesopause region in summer, i.e. in a region of a positive and negative temperature gradient, respectively. We assume that a periodic vertical displacement of the mean temperature profile (upward and downward shifts following each other) in long-term variability leads to such an anticorrelated temperature evolution at the different observation altitudes. This mechanism is confirmed by SABER observation on board the TIMED satellite.
The peculiarities of acoustic-gravity waves propagating in inhomogeneous polar thermosphere flows have been investigated. It is shown that a spectrum filtration and a change in amplitudes of acoustic-gravity waves occur in the region of polar thermosphere circulation. As a result, the waves with horizontal lengths of 500–700 km and periods of ∼ 10 min are predominated in satellite observations. We have shown that such spectral properties correspond to the waves which are blocked in the counter flow. The amplitudes of the blocked waves are greatly enhanced due to their interaction with the non-uniform flow. A ground-based observer registers these waves with periods from 30 min to more than 1 h, depending on the flow velocity. Taking in to account the interaction of the waves with the flows we can explain the discrepancy between the results of satellite and ground-based observations of acoustic-gravity wave in the polar regions.
We analyzed plasma scale height observations (about 80 km altitude) over the Eifel region (50°N, 6°E) observed from Kühlungsborn (54°N, 12°E) in the time interval 1959–2016 and OH* temperatures (center altitude 87 km) observed from Wuppertal (51°N, 7°E) in the time interval 1988–2016. In summer months both time series show a dominant oscillation with a period of about two decades (20–26 years) with amplitudes of about 180 m and 3 K, respectively. These two oscillations are anticorrelated, because their observation altitudes are located above and below the temperature minimum in the mesopause region in summer, i.e. in a region of a positive and negative temperature gradient, respectively. We assume that a periodic vertical displacement of the mean temperature profile (upward and downward shifts following each other) in long-term variability leads to such an anticorrelated temperature evolution at the different observation altitudes. This mechanism is confirmed by SABER observation on board the TIMED satellite.
The peculiarities of acoustic-gravity waves propagating in inhomogeneous polar thermosphere flows have been investigated. It is shown that a spectrum filtration and a change in amplitudes of acoustic-gravity waves occur in the region of polar thermosphere circulation. As a result, the waves with horizontal lengths of 500–700 km and periods of ∼ 10 min are predominated in satellite observations. We have shown that such spectral properties correspond to the waves which are blocked in the counter flow. The amplitudes of the blocked waves are greatly enhanced due to their interaction with the non-uniform flow. A ground-based observer registers these waves with periods from 30 min to more than 1 h, depending on the flow velocity. Taking in to account the interaction of the waves with the flows we can explain the discrepancy between the results of satellite and ground-based observations of acoustic-gravity wave in the polar regions.
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