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Evaluation of solar energetic particle pressure


Manuela Mallamaci

Sun undergoes a peak of activity every 11 years. This is the duration of the magnetic cycle, which has different effects on Sun and on interplanetary medium. During maximum, external solar layers are perturbed and phenomena such as flares and CME are much more frequent. They can accelerate population of high energy particles, protons essentially, named briefly SEP (Solar energetic particles), that can arrive at Earth and interact with geomagnetic field, producing in some cases severe storms and polar radio blackouts.

According to GOES measurement of 5 minute-averaged proton fluxes > 10 MeV, we say the start of a proton event to be the first of 3 consecutive data points with fluxes greater than or equal to 10 pfu (1). The end of an event is the last time the flux was greater than or equal to 10 pfu.

Using our solar flare list, we calculate pressure generated by solar wind and by SEP during the most intense events: i.e. X class flares and also in some cases M class flares. In particular, we consider data from EPAM/ACE and GOES. These spacecrafts give us proton fluxes, measured in higher energy channels, with respect to the solar wind one (see the tables 1. and 2. for information about energy range).

(1) 1 pfu = 1 particle / (cm^2*s*sr)



Channel
Mean energy
[keV]
Bandwidth
[keV]
1
56
21
2
88
47
3
150
80
4
250
126
5
424
270
6
789
473
7
1419
840
8
3020
2900

Table 1. LEMS120-ACE/EPAM detector energy channels [1]



Channel
Mean energy
[keV]
Bandwidth
[keV]
1
20
20
2
45
30

Table 2. GOES energy channels, available at [2]


On the basis of some calculations, we study the following periods of 2011 and 2012 (table 3.). In order to know more about plotted quantities click here.


year
15days period
flare - day
Start day GOES SEP
2011
2/8 - 16/8
30/8 - 13/9
17/9 - 1/10
27/10 - 10/11
X6.9 - 9/8
X2.1 - 6/9
X1.9 - 24/9
X1.9 -3/11
9/8
none
23/9
none
2012
16/1 - 30/1
20/1 - 3/2
29/2 - 14/3
10/5 - 24/5
29/6 - 13/7
5/7 - 19/7
16/10 - 30/10
M8.7 - 23/1
X1.7 - 27/1
X5.4 - 7/3
M5.1 - 17/5
X1.1 - 6/7
X1.4 - 12/7
X1.8 - 23/10
23/1
27/1
7/3
17/5
7/7
12/7
none

Table 3. Studied periods in 2011 and 2012.
Click on time interval to see related time evolution of solar wind and SEP pressure.


References
[1] Ace Science Center, http://www.srl.caltech.edu/ACE/, 1998
[2] Goddard Space Flight Center, http://omniweb.gsfc.nasa.gov/index.html, 1997