Mid-latitude Summer Nighttime Anomaly (MSNA) – observations and model simulations

Abstract

Abstract. In this paper, we present model simulations of the Mid-latitude Summer Nighttime Anomaly (MSNA) in the Northern Hemisphere, which is characterized by noontime dip and evening maximum in the diurnal variation of the ionospheric density. The simulations are carried out using SUPIM (Sheffield University Plasmasphere Ionosphere Model) for solar minimum at 135 • E longitude where MSNA is most pronounced in the Northern Hemisphere. The simulations are used to understand the relative importance of electric fields, and zonal and meridional winds in the formation of MSNA. The wind velocities measured by the Middle and Upper atmosphere radar (MU radar) and those obtained from the horizontal wind model (HWM93) are used. The results show that the formation of MSNA is closely related to the diurnal variation of the neutral winds with little contribution from the changes in the electric fields. The observed features of MSNA are better reproduced when MU radar winds are used as model input rather than HWM winds.

Three-dimensional electron density along the WSA and MSNA latitudes probed by FORMOSAT-3/COSMIC

“…Liu et al (2010) indicate that the two or three distinct regions of the MSNA results from a combination of the neutral wind effect in the geomagnetic frame, photoionization, and the thermal contraction of the ionosphere at sunset. The simulations of Thampi et al (2011) and Chen et al (2011) reach similar conclusions that the neutral wind is the dominant effect, and the zonal electric field can also contribute to modify the MSNA. Meanwhile, scientists Zakharenkova et al 2012;Cherniak et al 2014) examine storm effects providing further evidence to the pivot role of effective neutral wind in the formation of MSNA.…”

Midlatitude summer nighttime anomaly in NmF2 according to the data of vertical sounding in Alma-Ata

“…We then compared the results obtained by us in 2008 to the measurements conducted in Japan in July 2008 at the center of the northeastern Asia anomaly zone (Thampi et al, 2011). These measurements were con ducted by radio occultation, which makes it possible to obtain the electron concentration profile beginning from the bottom layer and up to heights substantially exceeding the height of the layer maximum.…”

“…These measurements were con ducted by radio occultation, which makes it possible to obtain the electron concentration profile beginning from the bottom layer and up to heights substantially exceeding the height of the layer maximum. Thampi et al (2011) showed that the local time corresponding to the night maximum peak depends on geographic latitude: the time shifts towards midnight at the increase in latitude. For the geographic latitude of 45°N…”

“…Modeling of the MSNA was performed with cur rent atmospheric-ionospheric models (Knyazeva et al, 2010;Karpachev et al, 2010;Thampi et al, 2011). Analysis of the measurement results and modeling presented the consideration of various mechanisms of MSNA formation, including a vertical shift of the layer due to the thermospheric meridional and zonal wind in the existing configuration of the geomagnetic field, ionospheric plasma drift in the crossed electric and magnetic fields, and variations in the plasma fluxes from the plasmasphere to the ionosphere.…”

Climatological modeling of horizontal winds in the mesosphere and lower thermosphere over a mid-latitude station in China

“…Thampi et al (2011) showed that the formation of the mid-latitude summer nighttime anomaly (MSNA) is closely related to diurnal variation in the neutral winds, but with little contribution from the changes in the electric fields. The observed features of the MSNA are reproduced better when MU radar winds are used as the model input rather than HWM93 winds.…”