Acta Geodaetica et Geophysica最新文献

This study focuses on the possible ionospheric anomalies before the Mw7.2 earthquake in Haiti on August 14, 2021. Based on the dual-frequency observation data of Global Navigation Satellite System (GNSS) stations and Global Ionosphere Maps (GIM) data products, the sliding interquartile range method was applied to detect and analyze the changes of ionospheric Total Electron Content (TEC) anomalies before the earthquake. The results show that the TEC anomalies over five GNSS stations show the common existence of anomalous times, which are July 28, August 1, August 2, August 7, and August 13, 2021, respectively. Combining space weather parameters and GIM, it is tentatively concluded that the TEC anomaly that appeared on August 1 (i.e., the 13th day before the earthquake) was not disturbed by geomagnetic storms and solar activity, and may be related to the breeding earthquake. An ionospheric anomaly close to 6 TECU was present near the epicenter 13 days before the earthquake, which is strongly associated with the peak variation of the equatorial anomaly. This suggests that an anomalously increased vertical electric field may have been generated before the earthquake, which in turn enhanced the “fountain effect” and created a strong northern hump.

Acoustic-gravity waves (AGWs) generated in the lower atmosphere can cause the ionosphere’s ionized plasma. Therefore, the electromagnetic signals transmitted from the navigation and communication satellites can be distorted based on AGWs propagating to upper atmosphere height and then disturbing the ionosphere. In this work, total electron content (TEC) was derived from dense Hubei continuously operating reference stations (HBCORS) to detect the potential ionospheric disturbance associated with a severe thunderstorm that hit Wuhan city on March 2, 2018. TEC values were examined under meticulous observation for the space weather indices. Furthermore, a de-trending algorithm, the so-called numerical divergence by multiple intervals, was applied to TEC sequences to detect the ionospheric disturbance due to the event. The slant TEC (STEC) variations near the thunderstorm area had a higher amplitude content than those that were away from it. The STEC deviations (dTEC) have been compared with a non-lighting day. Our findings indicated that the dTEC was insignificant compared with the day of the event. Afterwards, regional ionosphere maps (RIMs) were modeled through the HBCORS data around Hubei province. RIMs were employed to analyze the vertical TEC (VTEC) response to the thunderstorm. VTEC responses were detected by a proposed de-trend method so-called differences from the average value. The ionosphere showed a positive response up to 2 TECU, especially in the northern part of Hubei province where the maximum VTEC amplitude variations coincided with the thunderstorm influence. The findings are tentatively interpreted by lightning-induced electric fields and AGWs.

Since the Moon is less flattened than the Earth, most lunar GIS applications use a spherical datum. However, with the renaissance of lunar missions, it seems worthwhile to define an ellipsoid of revolution that better fits the selenoid. The main long-term benefit of this might be to make the lunar adaptation of methods already implemented in terrestrial GNSS and gravimetry easier and somewhat more accurate. In our work, we used the GRGM 1200A Lunar Geoid (Goossens et al. in A global degree and order 1200 model of the lunar gravity field using GRAIL mission data. In: Lunar and planetary science conference, Houston, TX, Abstract #1484, 2016; Lemoine et al. in Geophys Res Lett 41:3382–3389. http://dx.doi.org/10.1002/2014GL060027, 2014), a 660th degree and order potential surface, developed in the frame of the GRAIL project. Samples were taken from the potential surface along a mesh that represents equal area pieces of the surface, using a Fibonacci sphere. We tried Fibonacci spheres with several numbers of points and also separately examined the effect of rotating the network for a given number of points on the estimated parameters. We estimated the best-fitting rotation ellipsoid’s semi-major axis and flatness data by minimizing the selenoid undulation values at the network points, which were obtained for a = 1,737,576.6 m and f = 0.000305. This parameter pair is already obtained for a 10,000 point grid, while the case of reducing the points of the mesh to 3000 does not cause a deviation in the axis data of more than 10 cm. As expected, the absolute value of the selenoid undulations have decreased compared to the values taken with respect to the spherical basal surface, but significant extreme values still remained as well.