Ionospheric upwelling and the level of associated noise at solar minimum

Abstract. We have studied the ionospheric upwelling with a magnitude of above 1013 m−2 s−1 using the data during the European Incoherent Scatter Scientific Association (EISCAT) Svalbard Radar International Polar Year (IPY-ESR) 2007 campaign, which coincides with the solar minimum. The noise level in low-, medium- and high-flux upflows is investigated. We found that the noise level in high-flux upflow is about 93 %, while in the low and medium categories it is 62 % and 80 %, respectively. This shows that robust and stringent filtering techniques must be ensured when analysing incoherent data in order not to introduce bias to the result. Analysis reveals that the frequency of the low-flux upflow events is about 8 and 73 times the medium- and high-flux upflow events, respectively. Seasonal observation shows that the noise level in the upflow classes is predominantly high during winter. The noise is minimal in summer, with a notable result indicating occurrence of actual data above noise in the low-flux class. Moreover, the percentage occurrence of the noise level in the data increases with increasing flux strength, irrespective of the season. Further analysis reveals that the noise level in the local time variation peaked around 17:00–18:00 LT (local time) and minimum around 12:00 LT.