Analysis of superconducting gravimeter data during typhoon period using 3-D atmospheric model: case study of typhoon Nepartak
| Autor: | Yu, Ming-Yen, 余明晏 |
|---|---|
| Rok vydání: | 2017 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 105 Typhoon Nepartak caused a significant wind hazard in July, 2016. Weather station Cheng-Kung in Taitung recorded a highest wind speed of about 73 m/s, which broke the record in the last 20 years. The Central Weather Bureau(CWB) recorded lowest atmospheric pressure of 905 hPa. Superconducting gravimeter (SG) T49, located at satellite tracking station Yang-Ming-Shan (YMSM), provides long term, continual, high frequency and high precision gravity records. Because the track of Nepartak passed through southern Taiwan, T49 was able to detect gravity changes during typhoon period without disturbance of heavy rain. Using the gravity records of T49from 2013 to 2016, we calculated tidal parameters for the solid earth tide and ocean loading effects for correcting such effects. The polar motion effect was removed in the raw gravity. With all such effects removed, the gravity residual T49 contains only the atmospheric gravity effect which is computed using a 3-D model (Newtonian part) rather than the empirical, admittance-based method. We used 3-D atmospheric data from European Reanalysis Interim (ERA-Interim), established by European Center of Medium-Range Weather Forecast (ECMWF), to calculate the Newtonian attractions due to atmospheric mass change resulting from changes in pressure, temperature and humidity. With the SG data and the 3-D atmospheric gravity change model, we identified the specific gravity effects induced by typhoons. Based on the 3-D model, the air mass of typhoon Nepartak can cause gravity changes of up to 500 μGal in absolute value and 9 μGal in relative value. Temperature and humidty changes can cause gravity variations of up to 6 μGal. The air mass under the T49 gravity station can cause gravity changes of about 1 μGal over a long period and up to 0.8 μGal in high-frequency gravity oscillation. Compared to the empirical method, the 3-D model produces an atmospheric effect that is more consistent with the expected gravity change due to atmospheric solar tide change caused by day and night temperature fluctuations during Nepartak. The 3-D result was 3 μGal larger than that from the empirical method. The gravity residual of T49 corrected with the 3-D model results in a standard deviation of 0.61 μGal, which is smaller than the standard deviation of 1.51 μGal based on the empirical method. This suggests that the empirical method, based on a -0.35 μGal〖∙hpa〗^(-1) atmosphere-to-gravity admittance, is not appropriate for explaining gravity changes during Nepartak. The gravity residual corrected by the 3-D model did not show any sign of gravity change due to atmospheric loading. This suggests the inverted barometer (IB) effect occurred at sea near T49 during Nepartak. In order to see how non-IB could occur during typhoon period, over different typhoons we added a discussion using a second typhoon, Goni, occurring in August, 2015. After correcting for the 3-D atmospheric effect, the remaining gravity of T49 during Goni shows an empirical admittance of 0.14 μGal〖∙hpa〗^(-1). This suggests that the non-IB response has occurred. During typhoons Nepartak and Goni, the ranges of pressure change were almost the same. Compared to Goni, Nepartak had a lower lowest pressure change and larger 3-D gravity effects (2 μGal more). |
| Databáze: | Networked Digital Library of Theses & Dissertations |
| Externí odkaz: |
|