Altai State University, RUSSIA 26th E+CRS / 35th RCRC, 06 July 2018 - 10 July 2018 Altai State University, RUSSIA Solar energetic particles effect on the atmospheric electric field V.S. Makhmutov1, J. C. Tacza2, Y.I. Stozhkov1, J.-P. Raulin2 1 P.N. Lebedev Physical Institute RAS, Moscow, Russia 2 Center of Radioastronomy and Astrophysics Mackenzie (CRAAM), Mackenzie Presbyterian University, Brazil.

Abstract The AFINSA network (Atmospheric Electric Field Network in South America) is composed of eight electric field mill sensors installed in Brazil, Argentina and Peru. AFINSA provides continuous measurements of the atmospheric electric field (AEF). The main objective of the network is to obtain AEF daily curve under fair weather conditions, which we consider as our standard curve. We pretend to study deviations of the daily observations from the standard curve during several geophysical phenomena. In this paper, we investigate solar energetic particles effects on the AEF recorded in one of AFINSA’s sensors (CASLEO, Lat. 31.798°S, Long. 69.295°W, Altitude: 2552 masl). AEF data corresponds to the period between January 2010 - December 2015 when 15 SEP events occurred. To enhance possible small effects, a superimposed epoch analysis was used. We find a clear increase of about 10 V/m in the AEF records.

OUTLINE We investigate solar energetic particles effects on the Atmospheric Electric Field The main objective of the network is to obtain AEF daily curve under fair weather conditions. We pretend to study deviations of the daily observations from the standard curve during solar phenomena AEF data corresponds to the period between January 2010 - December 2015. A superimposed epoch analysis was used in the analysis We find a clear increase of about 10 V/m on the AEF records related to the solar proton events We discuss these results in terms of the electrical conductivity of the Earth ‘s atmosphere and its time variability.

1. INTRODUCTION Atmospheric Electric Field persists in FW regions  Measures on the world‘s oceans show Carnegie Curve in FW conditions. The Global Atmospheric Electric Circuit (GAEC)  Earth’s surface and ionosphere  links charge separation in DW regions with current flow in FW regions. I'll start with some general information on the atmospheric electric field. The AEF persists in Fair Weather regions (For Fair weather regions we understand regions with no clouds, no thunder, speed wind less than 8 m/s) and this field shows a daily variation in Universal Time knowns as the Carnegie Curve, which was measured in the oceans. This AEF is produced by the potential difference in this region. It is believed that this potential differential is maintained by thunderstorms occurring in remote places and this is evidenced by the similarity between the Carnegie curve and the global variation of thunderstorms. This concept is known as the Global Atmospheric Electric Circuit which is formed between the Earth's surface and the ionosphere and links charge separation in Disturbed Weather regions with current flow in FW regions. Solar effects and their relationships with the dynamics of the GAEC have been studied indirectly monitoring the departures from the AEF in FW. Such effects include solar flares, SPEs and Forbush decrease. However, the results are ambiguous and the mechanisms are not well defined. So, the obective of this work es find possible solar effects on the AEF in FW regions. GAEC may be affected by solar phenomena (e.g. solar flares, solar proton events, Forbush decrease). Objective: Search for possible solar effects on the AEF in FW regions.

INSTRUMENTATION MET STA CARPET MET STA CAS1 CAS2 2550 m

DATA ANALYSIS Calculate monthly mean curves of the diurnal variations of the AEF in FW (standard curve). Meteorological station is located at 1.5 km from the AEF monitor. 2. AEF daily curves during solar events were compared with our standard curves  excess of AEF 3. We use the superposed epoch analysis (SEA) in order to enhance weak effects on the curves during solar flares. Subsets of data (AEF daily curve minus the standard curve) “0” – time is a start of solar event (X-ray, GOES) The methodology adopted follows the steps described here. First, we calculate monthly mean curves of the diurnal variations of the AEF in FW (this is our standard curve). It is important to say that the weather station is located 1,5 km apart. Second, AEF daily curves were compared with our standard curves during solar events. Third, we may use the superposed epoch analysis (SEA) in order to enhance weak effects. The SEA rely on selecting subsets of data (in our case the AEF daily curve minus the standard curve), and our key events is the start of the solar event.

List of SOLAR FLARES used in analysis (2010-2015; 114 events; No solar protons) Date Start, UT Imp.

RESULTS CAS2 114 solar flares No particles. KP<4 ; Dst >-50 nT Superposed epoch analysis for 114 solar flares CAS2 114 solar flares No particles. KP<4 ; Dst >-50 nT No significant effects. -1 day +5 days

List of SOLAR PROTON EVENTS used in analysis (2011-2015; Jp>100 MeV) Date

RESULTS Superposed epoch analysis for 15 SEP events 15 SPEs very intense (>100 MeV). KP<4 ; Dst >-50 nT Possible significant effect: 10 V/m -1 day +2 days

RESULTS IONOSPHERE 𝝈 SPE ATMOSPHERE DW FW GROUND △V DW FW GROUND Global Atmospheric Electric Circuit On the other hand, the SPEs analysis shows a significant effect on the AEF values. First, the 2-hour decrease of AEF at the same time of maximum increase of proton flux. Second, an increase is noted. These opposite variations may be due to two different physical processes. Excess of precipitating protons during a SPE or lack of precipitating protons during a Forbush decrease may led to changes in the atmospheric electrical conductivity. First, we investigate the decrease of the AEF values. During the SPE there is an increase of ionization producing a high conductivity and, a reduction of AEF is expected, such as shown in figure 3. The second effect corresponds to an increase on the AEF values. This variation is also found statistically significant when using the SEA technique for all the other SEPs (Figure 4). These results are consistent with the model proposed by Farrell and Desch [7], which suggests that SPEs can increase atmospheric conductivity above electrical storms (disturbed weather regions). This allows more current to flow upstream to the GAEC and thus increase the AEF in FW regions. However, we did not observe a significant decrease on the AEF values as observed in Figure 3 at the beginning of the SPE event. This may be due to the fact that the SEP of May 17, 2012 was the only that produced a GLE event during the studied period. The SPEs included on the SEA technique were intense but not enough to cause changes in the ionization of the atmosphere. Global Model proposed by Farrell and Desch (GRL, 29, 2002): SPEs can increase atmospheric conductivity above electrical storms (DW regions). This allows more current to flow upstream to the GAEC and thus increase the AEF in FW regions.

SUMMARY 1. We use a superposed epoch analysis of excesses of AEF: (i) during 114 solar flares (2010-2015; no particles); (ii) during 15 SPEs (2011-2015). 2. No significant effect was found on the AEF values during solar flares (without solar protons). 3. SPEs can modify the conductivity in areas of electrical storms (disturbed weather regions) affecting the GAEC in FW regions. We find a clear increase of about 10 V/m on the AEF records related to the solar proton events. 4. During SPEs the height of the D-layer of the ionosphere can be decreased (by ~10 %, from ~ 60 km to 55 km) and it gives an increase of AEF about ~ 10%. It consists with the observational data. So to summarise the main points of my talk… In this paper we investigated the effect of solar events on the GAEC through AEF variations in FW regions. No significant effect was found on the AEF values during solar flares. However, very intense events (GLE and Forbush decrease) can produce changes on the ionization which modifies the atmospheric conductivity and, therefore, altering the AEF in FW regions. Also, SEPs can modify the conductivity in areas of electrical storms (disturbed weather regions) affecting the GAEC in FW regions. That brings me to the end of my presentation, thank for your attention.

Thank you very much for your attention

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