Decline of geomagnetic and ionospheric activity at earthquake during spotless Sun

We investigate the geomagnetic and ionospheric effects of seismic activity during 1954 Sun spotless days (SSL) from 1995 to 2020. Two subsets of earthquakes (EQ) are evaluated for 676 events observed with the depth D1 ≤ 30 km and 1278 events with D2 > 30 km and the total set SSL. Newly developed 1 h geomagnetic index Hpo and the ionospheric W_EQ index are used for the comparisons with the daily peak earthquake. The ionosphere W_EQ index is derived at the EQ epicenter from JPL GIM-TEC map within the cell of 2.5°×5°, in latitude φ and longitude λ surrounding the epicenter at radius of about 200 km. We use the method of superposed epoch with the zero epoch time t₀ taken at EQ to extract peak values of Hpo and W_EQ during t₀-24 h ≤ t < t₀ (preEQ) and t₀ < t ≤ t₀ + 24 h (postEQ). It is found that the magnitude of Hpo(t₀) is less that the both peaks of Hpo(preEQ) and Hpo(postEQ) in 91 % of events independent of EQ’s depth. Similar effect is observed with the peak of the positive/negative ionosphere indices and the absolute values of |W(preEQ)| and |W(postEQ)| the both exceeding |W_EQ| in 77 % of events. The seismic activity tends to increase towards the solar minimum when SSLs occur. Our results provide evidence that EQ-related geomagnetic and ionospheric activities experience decline of intensity at the time of EQ under SSL.     

短波红外全天时自主天文导航技术展望

基于2微米全天巡天（2MASS）短波红外巡天点源星表,分别从白天可探测恒星分布、天空背景辐射与大气传输、传感器性能和光学系统视场大小等方面,分析了短波红外波段相对于可见光波段,在大气层内白天观星实现全天时天文导航的优势,并展望了其发展方向。