Atmosphere‐ionosphere conductivity enhancements during a hard solar energetic particle event

Abstract

, a solar energetic particle (SEP) event caused the largest recorded solar proton ground level event since 1956. Serendipitously, a balloon-borne experiment intended to measure effects of relativistic electron precipitation was aloft over Antarctica ($32 km; near 70 S, 345 E geographic) throughout the duration of the SEP event, including the fast ($6 min) onset. The balloon instrumentation included dc electric field and scalar electrical conductivity sensors. The observed conductivity increased by nearly a factor of 20 above ambient with the SEP event onset and returned to within a factor of two above normal levels within 17 h. Results from a newly developed, globally applicable atmosphere-ionosphere conductivity model based on the Sodankylä Ion and Neutral Chemistry (SIC) model suggest that proton-induced ionization was directly responsible for the observed conductivity increase at the balloon. Model input for this event included estimates of ionization from energetic particle precipitation and rigidity cutoffs.Altitudes between 20 and 150 km were considered during model runs. The results show a maximum conductivity increase near 60 km of more than 600-fold directly after SEP event onset. Relatively small conductivity enhancements (two-to fivefold) are suggested to have occurred above 70 km as a result of SEP ionization, while almost no enhancement is thought to have occurred above 95 km. These results quantify the real effect that an SEP-event can have on atmosphere-ionosphere electrical conductivity on a large, nearly global scale and provide a detailed comparison to one of the few direct stratospheric conductivity observations made during an SEP event.

Atmospheric ionization by high‐fluence, hard‐spectrum solar proton events and their probable appearance in the ice core archive

“…The low‐energy calculations follow the approach described in Jackman et al . [] [see also Verronen et al , ; Jackman et al , ; Kokorowski et al , ]. The energy deposited in altitude bin i by protons with kinetic energy E and pitch angle θ is given by using the range energy relation [ Bethe and Ashkin , ; Whaling , ; Sternheimer , ; Green and Peterson , ]: with A = 2.71 × 10 −3 and B = 1.72 for 1 ≤ E ≤ 70 MeV.…”

Book of Proceedings: Ninth Workshop, Sunny Beach, Bulgaria, May 30 - June 3, 2017

“…One-minute-averaged GOES 11 integral proton channels January 20, 2005. Channels 11-17 are plotted for integral amounts greater than 1, 5, 10, 30, 50, 60 and (Kokorowski et al, 2012). However, this case is not always valid: the stratospheric column resistance R S = R SB + R SA can become comparable to the tropospheric resistance if a layer exists in the stratosphere of highly reduced conductivity, as predicted by Tinsley (2005) and Tinsley and Zhou (2006) cited further as TZ06.…”

“…The specific energy spectrum of proton flux during the considered SPE determines enhancement of conductivity above 30 km up to two orders of magnitude or more (Kokorowski et al, 2012, their Fig.9) when there are no pre-existing layers of reduced σ. This conductivity increase leads to expressed growing of currents J IC formed below the ionospheric structures of trans-polar potential which 'extend' the closure region of ionospheric currents.…”

Book of Proceedings Tenth Workshop Primorsko, Bulgaria 2018

“…As result of the strong ionization, conductivity σ also increases. The model results [Kokorowski et al, 2012] in Fig.2a demonstrate the conductivity profile at the balloon coordinates before (at 06:00 UT) and after (at 09:00 UT) arrival of SPE. …”

“…Data from GOES-10 for solar proton flux are demonstrated in Fig.1a [Kokorowski et al, 2012]. Simultaneous balloon-borne measurements in Antarctic stratosphere are represented for conductivity σ (Fig.1b), the vertical electric field Ez (Fig1c) and the related current Jz (Fig.1d).…”