Direct and Indirect Thermospheric Heating Sources for Solar Cycles 21–23

Abstract

Solar variability is often cast in terms of radiative emission and the associated long-term climate response; however, growing societal reliance on technology is creating more interest in day-today solar variability. This variability is associated with both solar radiative and solar wind emissions. In this paper we explore the combined effects of radiative and solar wind fluctuations at Earth. The fluctuations in radiative and geomagnetic power create an extended interval of solar maximum for the upper atmosphere. We use a trio of empirical models to estimate, over the last three solar cycles, the relative contributions of solar extreme ultraviolet (UV) power, Joule power, and particle kinetic power to the Earth's upper atmosphere energy budget. Daily power values are derived from three source models. The SOLAR2000 solar irradiance specification model provides estimates of the daily extreme and far UV solar power input. Geomagnetic power is derived from a combination of satelliteestimated particle precipitation power and an empirical model of Joule power from hemispherically integrated estimates of high-latitude energy deposition. During the interval 1975 to 2003, the average daily contributions were: particles -36 GW, Joule -95 GW and solar -464 GW for a total of 595 GW. Solar wind-driven geomagnetic power provided 22% of the total global upper atmospheric energy. In the top 15 power events, geomagnetic power contributed two-thirds of the total power budget. In each of these events, Joule power alone exceeded solar power. With rising activity, Joule power becomes the most variable element of solar upper atmosphere interactions.

Space Weather: Historical and Contemporary Perspectives

“…Studies of orbits of satellites at low Earth altitudes, and of satellites that have low altitude perigees, yield data that provide some of this atmospheric information (e.g., King-Hele 1992; Knipp et al 2004;Moe and Moe 2011).…”

Ionosphere-thermosphere (IT) response to solar wind forcing during magnetic storms

“…The effects of particle precipitation have been reported for decades -auroral emissions, intense field-aligned currents, enhanced conductivity are examples, but only relatively recently has the relative contribution of particle energy to the total storm energy budget been estimated. In a comparison of particle precipitation with solar radiation and Joule heat, Knipp et al (2004) arrived at a ratio of particle to Joule heat of approximately 1:10 for large storms. In our study of the August 2011 storm, we estimated the precipitation power as well as the observed Poynting flux and reached similar ratios (Huang et al 2014a).…”

“…This assumption is based on the effect of particle precipitation which gives rise to intense auroral emissions and high conductivity in the auroral zone (Evans et al 1977;Vondrak & Robinson 1985;Fuller-Rowell & Evans 1987;Coumans et al 2004, and many others). While conductivity is essential to Joule heating of ions, it was not until comparisons of energy input from solar radiation, electromagnetic waves in the form of Poynting flux, and particle precipitation were carried out that the relative contributions to the IT energy budget were realized (Knipp et al 2004;Huang et al 2014a). In these and other studies, it was shown that Poynting flux is by far the dominant source of energy into the IT system, with typical ratios of 3 to 10 of Poynting flux to particle precipitation power.…”

Variability of ionospheric TEC during solar and geomagnetic minima (2008 and 2009): external high speed stream drivers

“…Here we will focus exclusively on interplanetary (solar wind) drivers for the ionospheric and atmospheric activity. Analysis of thermospheric heating in 1975-2003 based on the Dynamics Explorer had shown that Joule heating was the major contributor to variability of the thermospheric power and dominated the auroral zone (Knipp et al, 2004). Recently, Knipp et al (2011) estimated the Poynting flux sorted by solar wind flow type.…”