Ionospheric climatology and variability from long-term and multiple incoherent scatter radar observations: variability

Abstract

Abstract. Long-term incoherent scatter radar (ISR) observations are used to study ionospheric variability for two midlatitude sites, Millstone Hill and St. Santin. This work is based on our prior efforts which resulted in an empirical model system, ISR Ionospheric Model (ISRIM), of climatology (and now variability) of the ionosphere. We assume that the variability can be expressed in three terms, the background, solar activity and geomagnetic activity components, each of which is a function of local time, season and height. So the background variability is ascribed mostly to the day-to-day variability arising from non solar and geomagnetic activity sources.(1) The background variability shows clear differences between the bottomside and the topside and changes with season. The Ne variability is low in the bottomside in summer, and high in the topside in winter and spring. The plasma temperature variability increases with height, and reaches a minimum in summer. Ti variability has a marked maximum in spring; at Millstone Hill it is twice as high as at St. Santin. (2) For enhanced solar activity conditions, the overall variability in Ne is reduced in the bottomside of the ionosphere and increases in the topside. For Te, the solar activity enhancement reduces the variability in seasons of high electron density (winter and equinox) at altitudes of high electron density (near the F2-peak). For Ti, however, while the variability tends to decrease at Millstone Hill (except for altitudes near 200 km), it increases at St. Santin for altitudes up to 350 km; the solar flux influence on the variability tends to be stronger at St. Santin than at Millstone Hill.

Millstone Hill ISR observations of upper atmospheric long-term changes: Height dependency

“…The majority of the data, however, is from the 1976–2010 period when standardized data processing procedures have been applied. Previously we used this latter part of data (until 2002) to construct climatology models of the ionosphere [ Holt et al , 2002; Zhang et al , 2005b], the ionospheric convection model [ Zhang et al , 2007], and the ionospheric variability model [ Zhang and Holt , 2008]. Data for the period 1976–2007 were also used in the trend study by Holt and Zhang [2008].…”

Day‐to‐day variability and solar preconditioning of thermospheric temperature over Millstone Hill

“…Variability in the physical state of the upper atmosphere can be significant but in general is not well understood. Some progress has recently been achieved primarily in characterizing variability in ionospheric electron density [see Rishbeth and Mendillo , ] and plasma temperatures [see Zhang and Holt , ]. However, variability in thermospheric parameters, and in particular, their day‐to‐day variability, has been less pursued due to the relatively fewer observations available.…”

Global and regional trends in ionospheric total electron content

“…Theoretical and experimental ionospheric trends have thus far been determined only for layer parameters, such as E and F peak heights, peak densities and critical frequencies, measured by ground‐based ionosondes and radars. Extensive databases of the height and concentration of the layer's peak and of ion temperatures are interpreted typically in terms of background (mainly day to day) variability, solar activity (using the solar 10.7 cm radio flux, F 10.7 ) and geomagnetic activity (using the geomagnetic index, Ap ), each a function of local time, height and season [ Zhang and Holt , 2008; Holt and Zhang , 2008]. Such trend studies are necessarily limited because global coverage is incomplete (especially in the Southern Hemisphere), regional variability can be significant, and the adopted relationships of the various ionospheric parameters and the removal of solar and geomagnetic effects vary among different analyses [ Bremer et al , 2004; Laštovička et al , 2006; Jarvis , 2009].…”