The discovery of apparent large (V/m) electric fields within the mesosphere suggests that this region is more active electrically than originally suspected. High-latitude observations have been particularly productive in developing new concepts regarding mesospheric electrodynamics. Several high-latitude observations of large mesospheric fields have been made under both quiet and aurorally active conditions but always below heights where enhanced ionizing radiations could significantly penetrate. Two measurements from Andoya, Norway, have also produced an anticorrelation of horizontal electric field directions with neutral wind velocities, leading to the theoretical description of a newly defined mechanism for V/m electric field generation involving wind-induced separation of charged aerosols. Evidence for mesospheric aerosols and winds exists at all latitudes but is most evident at high latitudes during the appearance of noctilucent and/or polar mesospheric clouds.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/JD094iD12p14661%4010.1002/%28ISSN%292169-8996.NCLOUDS1

Electrodynamics of the high-latitude mesosphere

The results of rocket measurements of ozone and nitric oxide concentrations, vertical component of the electric field strength, positive ion density, and temperature of the middle atmosphere during the extremely strong solar proton events (SPE) of October 1989 are presented. The measurements were taken in the southern hemisphere in the Indian Ocean (40 o- 60oS and 45o-75oE) on board the research vessel Akadernik Shirshov. A great increase in ion densities above -30 km and nitric oxide concentrations above-40 km with maximum (NO) -2x 10 9 cm '3 at 45- to 55-km heights were observed during the SPE. A decrease in ozone concentrations above -3 5 km with the maximum decrease of about 20-25% at-50-kin height and cooling of the atmosphere at -40- to 60-km heights with the maximum temperature decrease of about 14oK near 50 km were also observed. An unexpectedly large value of the vertical electric field strength of 12 V/m was detected in the lower mesosphere at about 58 km at 58o30'S during the SPE. The obtained results on ozone, nitric oxide, ion concentration, and temperature qualitatively agree with the existing photochemical concepts on the impact of solar proton events on the middle atmosphere, while the measured cooling of the stratopause is greater than that predicted by theoretical models. The increase of the vertical electric field strength observed during the SPE points out a very high electrical activity of the mesosphere and unknown generation mechanisms of electrical phenomena in the middle atmosphere.

Middle atmosphere response to the solar proton events of October 1989 using the results of rocket measurements

Mean ionic mass and conductivity, the product of mobility and ion concentration, are important in calculations of low-frequency propagation. Progress made mostly over the last decade concerning these parameters is reviewed. The mean positive ion mass has a range of about 90±35 amu with lighter masses more prevalent at the higher altitudes. The mean negative ion mass is generally greater and reaches a peak value of 300 amu near 35 km. Reduced mobilities μ0 for both positive and negative ions appear to lie within 1.6±0.6 cm2 (V s)−1. Somewhat finer resolution of μ0 with altitude is tabulated in the text. It is argued that ion concentrations and hence total conductivities are easily and well defined where galactic cosmic rays are the dominant ionization source and electron concentrations are negligible.

Ionic mobility, mean mass, and conductivity in the middle atmosphere from near ground level to 70 km

Recent measurements of middle atmospheric electric fields and related parameters

Electrical properties of the middle atmosphere

Solar effects on middle-atmosphere electrical parameters, as demonstrated by eclipse-associated responses of conductivity, ion mobility, and charge density, are considered for the total solar eclipses at Red Lake, Ontario, Canada on February 26, 1979 and at San Marco range, Kenya, on February 16, 1980. Negative-conductivity measurements for the Canadian eclipse and probe-current measurements for the Kenyan eclipse demonstrate a rapid loss of free electrons below 80 km at totality. During the Kenyan eclipse, positive-ion responses were different for each of two distinct ion mobility groups. Between 45 and 60 km, eclipse-related positive-ion responses are associated with the low-mobility ions. It is shown that these ions are lost at totality and that an excess buildup occurs following totality. Above 70 km, positive-ion loss at totality is associated with the more mobile ions and only low-mobility positive ions are measured in this region. The buildup in total ion density following totality is thought to result from a reduction in ion loss associated with weak-electron recovery in the region.

J. D. Mitchell

Papers

Middle-atmosphere positive ion measurements during solar eclipses