Characteristics of equatorial plasma bubble zonal drift velocity and tilt based on Hong Kong GPS CORS network: From 2001 to 2012

Hong Kong (22.3N, 114.2E, dip: 30.5N; geomagnetic 15.7N, 173.4W, declination: 2.7W) is a low-latitude area, and the Hong Kong Continuously Operating Reference Station (CORS) network has been developed and maintained by Lands Department of Hong Kong government since 2001. Based on the collected GPS observations of a whole solar cycle from 2001 to 2012, a method is proposed to estimate the zonal drift velocity as well as the tilt of the observed plasma bubbles, and the estimated results are statistically analyzed. It is found that although the plasma bubbles are basically vertical within the equatorial plane, the tilt can be as big as more than 60 eastward or westward sometimes. And, the tilt and the zonal drift velocity are correlated. When the velocity is large, the tilt is also large generally. Another finding is that large velocity and tilt generally occur in spring and autumn and in solar active years.