N_mF₂ enhancement during ionospheric F₂ region nighttime: A statistical analysis based on COSMIC observations during the 2007–2009 solar minimum

Abstract

In this paper the global features of NmF2 enhancement occurring during ionospheric F2 region nighttime (the period when the sunlight is occulted by the Earth in the altitudinal range of ionospheric F2 region) and lasting for more than 2 h were investigated based on Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) measurements during the 2007–2009 solar minimum. This nighttime enhancement of NmF2 mainly appears at the latitudes with dips larger than 45° in the winter hemisphere in solstice seasons. The magnitude of NmF2 enhancement reaches latitudinal maxima (minima) at the geomagnetic latitudes of about 40°–50° (60°–70°), with larger magnitudes in the northern winter hemisphere than in the southern winter hemisphere. The longitudinal variation of nighttime enhancement is also evident; especially the magnitude of NmF2 enhancement shows a significant longitudinal modulation in the southern winter hemisphere. The controlling factors of the spatial variations of NmF2 nighttime enhancement were analyzed. The longitudinal variation of NmF2 nighttime enhancement is suggested to be related to the longitudinal differences in background NmF2, thermospheric density, and interhemispheric plasma transport, and the latitudinal variation of NmF2 nighttime enhancement is possibly related to the latitudinal variations of geomagnetic inclination and the plasma storage in the topside ionosphere and the plasmasphere. The configuration of the geomagnetic field plays an important role in the longitudinal and latitudinal variations of NmF2 nighttime enhancement.

Deep Ionospheric Hole Created by Sudden Stratospheric Warming in the Nighttime Ionosphere

“…Different mechanisms were proposed to explain this phenomenon, including plasmaspheric flux from the conjugate ionosphere (Evans, ), increased downward flux from the plasmasphere (e.g., Bailey et al, ; Jakowski & Forster, ), and enhanced meridional neutral wind (Mikhailov et al, ). Our analysis of TEC data following several SSW events indicates that on average a postmidnight increase in electron density is very strong at 75°W and maximizes at 30–33°N (Figure ), consistent with Constellation Observing System for Meteorology, Ionosphere, and Climate observations (Chen et al, ). During the SSW of 2013, the latitudinal peak in the postmidnight density increase shifted poleward by ~5–7°, leading to an increase in electron density and TEC at 40–50°N on 18 January 2013 (Figure ).…”

“…A postmidnight increase in midlatitude ionospheric electron density is a well‐documented phenomenon (e.g., Chen et al, ; Farelo et al, , and references therein). Different mechanisms were proposed to explain this phenomenon, including plasmaspheric flux from the conjugate ionosphere (Evans, ), increased downward flux from the plasmasphere (e.g., Bailey et al, ; Jakowski & Forster, ), and enhanced meridional neutral wind (Mikhailov et al, ).…”

Nighttime Enhancements in the Midlatitude Ionosphere and Their Relation to the Plasmasphere

“…During solstice, midlatitude enhancements are observed in the winter hemisphere (Figure ), likely corresponding to the NWA feature (see Jakowski et al, , and the references therein). Another recent study used N m F 2 measurements from the COSMIC constellation to find that the enhancements maximize at the magnetic latitudes of about 40° –50° in the winter hemisphere (Chen et al, ). The CHAMP and DMSP density enhancements in general have consistent latitudinal structures.…”

The importance of neutral hydrogen for the maintenance of the midlatitude winter nighttime ionosphere: Evidence from IS observations at Kharkiv, Ukraine, and field line interhemispheric plasma model simulations

“…Their simulation showed that nighttime enhancements of N m F 2 can occur when the plasmasphere becomes sufficiently full. Numerous experimental studies support the importance of the plasmaspheric flows for the formation of the nighttime electron density enhancements [e.g., Bertin and Papet‐Lepine , ; Davies et al ., ; Standley and Williams , ; Williams and Jain , ; Bailey et al ., ; Jakowski and Förster , ; Farelo et al ., ; Dabas and Kersley , ; Jakowski et al ., ; Chen et al ., ].…”

“…A number of mathematical modeling studies of the coupling between the F region and the plasmasphere were published over the past 40 years [e.g., Moffett and Murphy, 1973;Banks, 1974, 1975;Marubashi and Grebowsky, 1976;Bailey et al, 1978Bailey et al, , 1979Marubashi, 1979;Murphy et al, 1979Murphy et al, , 1980Quegan et al, 1982;Nagmoosh and Murphy, 1983;Schunk, 1988;Mikhailov et al, 2000;Richards et al, 2000;Pavlov and Pavlova, 2005;Jee et al, 2005]. Williams and Jain, 1984;Bailey et al, 1991;Jakowski and Förster, 1995;Farelo et al, 2002;Dabas and Kersley, 2003;Jakowski et al, 2015;Chen et al, 2015].…”