Analyzing Of The Characteristics Of Ionospheric Disturbances Derived By Medium And Small Geomagnetic Stormsbased On GNSS Data

The ionosphere is one of important parts of sun-earth space environment and it is closely related to the living environment of human being. Geomagnetic storms caused by solar activities and many other factors can lead to ionospheric disturbances. The anomaly disturbances of ionosphere not only influence the accuracy of GNSS (Global Navigation Satellite System) navigation, positioning and timing, but also make severe affect to communication systems, space vehicles and so on. Most previous researchs focused on the ionospheric response to the large geomagnetic storms, however, there is lack of study about ionospheric disturbances of medium and small geomagnetic storms. Therefore, this paper investigated the charateristics of ionospheric disturbances caused by medium and small geomagnetic storms systematically. This study is important to improve the accuracy of GNSS navigation, positioning and it is useful to further understand the influences on the ionosphere of geomagnetic storms with different grades. With the development of GNSS, dynamic monitoring based on GNSS observations is considered to be an effective and reliable way for ionosphere detection. This paper used dense GNSS observation network in North America to conduct feature extraction, and statistics analysis of ionospheric disturbances during medium and small geomagnetic storms between January 1,2012 and December 31,2013. The main contents are as follow.(1) It has realized the ionospheric total electron content inversion with high accuracy and temporal resolution by combining carrier phase and pseudorange observations on the basis of a detailed pretreatment of the original double-frequency observation data of GNSS tracking network;(2) By introducing multiresolution wavelet transform method, the TEC disturbances caused by medium and small geomagnetic storms were extracted, and then use the SADM-GPS (statistical angle of concatenated and doppler method for GPS)method to eliminate the effect from satellite motion on the calculation of traveling ionospheric disturbance parameters;(3) Using 352 GNSS tracking stations to calculate traveling ionospheric disturbance parameters (horizontal phase velocity, horizontal azimuth and period) during medium and small geomagnetic storms between January 1,2012 and December 31,2013 in North America;(4) Statistical analysis the above calculation results, we can note that:the amplitude of disturbances during medium and small geomagnetic storms are between 0.2 TECU and 2.5 TECU, the range of horizontal velocities and azimuths are 100-600 m/s and 120°～240° respectively; the range of period are between 20 min～128min. The amplitude and horizontal phase velocity of TEC disturbances are smaller in winter than any other seasons during geomagnetic storms, and the TEC disturbances caused by small geomagnetic storms are smaller than large and medium geomagnetic storms, its amplitudes are between 0.2 TECU and 1.2 TECU, with obvious disturbance phenomenon. For small geomagnetic storms, the range of horizontal velocities and azimuths are 100-280 m/s, and 140°～240° respectively; the range of period are also between 20 min～120 min; Finally, the physical mechanism of traveling ionospheric disturbance during the medium and small geomagnetic storms on the basis of the above results are discussed preliminarily.