Observations of a positive storm phase on September 10, 2005

<p>In this study, we present multi-instrument observations of a strong positive phase of ionospheric storm, which occurred on September 10, 2005 during a moderate geomagnetic storm with minimum <em>D</em>_st=-60\&nbsp;nT and maximum <em>K</em>_p=6\textendash. The daytime electron density measured by the Millstone Hill incoherent scatter radar (42.6\textdegreeN, 288.5\textdegreeE) increased after 13\&nbsp;UT (\~8\&nbsp;LT) compared with that before the storm. This increase is observed throughout the daytime, lasts for about 9\&nbsp;h, and covers <em>F</em>-region altitudes above \~230\&nbsp;km. At the altitude of 300\&nbsp;km, the maximum increase in <em>N</em>_e reaches a factor of 3 by 19:30\textendash20:00\&nbsp;UT and is accompanied by a \~1000\&nbsp;K decrease in electron temperature, a \~100\textendash150\&nbsp;K increase in ion temperature, and a strong upward drift. Observations by Arecibo ISR (18.3\textdegreeN, 293.3\textdegreeE) reveal similar features, with the maximum increase in electron density reaching a factor of 2.5 at 21:30\&nbsp;UT, i.e. 1.5\textendash2\&nbsp;h later than over Millstone Hill. The GPS TEC data show that the increase in electron density observed at Millstone Hill and Arecibo is only a part of a global picture reflected in TEC. The increase in TEC reaches a factor of 2 and covers middle and low latitudes at 19\&nbsp;UT. At later times this increase moves to lower latitudes. A combination of mechanisms were involved in generation of positive phase. The penetration electric field resulted in <em>N</em>_e enhancements at subauroral and middle latitudes, the TAD/TID played an important role at middle and lower latitudes, and increase in O/N₂ ratio could contribute to the observed positive phase at middle and lower latitudes. The results show the importance of an upward vertical drift at \~140\textendash250\&nbsp;km altitude, which is observed for sustained period of time and assists in the convergence of ionization into the <em>F</em>-region.</p>