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P. Diego, M. Laurenza, M.Storini, and S. Massetti
IAPS/INAF - Italy
Characterization of the space
environment at Mercury’ orbit
Index
• Space Climate study to point out environmental conditions
between 0.3 and 0.47 A.U. for BepiColombo mission.
 Short–term and long–term solar variability are considered
 Results are compared to OMNI data at 1 A.U.
• Mercury’s magnetosphere response to different SW inputs are
considered
• Suprathermal particles flux occurrences and fluxes are analyzed
Solar Activity - Short Term Variability
• Corotating Structures; 27-days recurrent streams,
(HSSs from Coronal Holes) ,
Solar Magnetic Sectors
• Transient Solar Phenomena; Solar Flares, ICMEs (e.g. Magnetic Clouds
(MC), Non Compressive Density Enhancements (NCDE))
In order to identify occurrences of
persistent conditions at Mercury’s
orbit only the largest (duration >
12h) perturbations have been
selected.
The durations of this short term
variability span from hours to
days.
Shorter time-scale fluctuations are
not considered for our purpose.
Solar Activity Long Term Variability
• Solar Activity cycle; duration, amplitude
and phases, Gnevyshev Gap
• Even and odd solar cycles;
The time scale of this variability spans
from few months (cycle increase /
decrease, G-Gap,…) up to 22 years (Hale
cycle)
Data Used and Events Selection
Helios 1 and 2 hourly data for period
from 1975 to 1980 between 0.3 and 0.47
A.U. (about 2x30 days/year)
Perturbation category individuated are:
• HSSs from CH (e.g. Mavromichalaki et
al. 1988)
• ICME from active regions. Among
them we selected:
• Magnetic Clouds (MC – Burlaga
1981)
• Non Compressive Density
Enhancements (NCDE – Gosling
et al. 1977)
22 HSSs, 11MCs, and 27 NCDEs have
been identified
Helios 1 data for April 1977.
Orange selections indicate HSSs, grey a NCDE, and
blue a Magnetic Cloud
Number of selected perturbations for each Helios, 1and 2, passage at Mercury’s orbit
along with Solar Cycle n. 21 profile.
Interplanetary Shock numbers (Volkmer and Neubauer, 1985) are superimposed (red
markers).
Solar Perturbations
occurrences are displayed
in % of total observation
time.
High percentage could
depend on reduced time of
observations.
Why do we separate classes of perturbations?
Because the relative percentage of each class depends on long term solar activity variations
such as phase, amplitude.
• The phase of cycle; by definition is the temporal evolution of Sunspots Number
• Odd numbered cycle features; enhanced transient activity during rise and maxima, higher
amplitude of maxima (Cliver et al. 1996)
• Even numbered features; enhanced co-rotating solar structure during descending phases
• The amplitude of solar cycle determines the ratio of active regions and CH at mid solar
latitudes
While the first two are easily identified, the third one should be forecasted.
To forecast the solar cycle amplitude we
could study the persistence of polar
magnetic structures. In fact for some
dynamo models [e.g. Dikpati et al., 2004;
Choudhuri et al., 2008] the polar field is
essential for the generation of sunspots of
the subsequent cycle, although their
persistence could lead to opposite results
when predicting the sunspots maximum
amplitude.
Polar CH lifetime and extension are inversely related to the strength of Sun's polar fields of
the following activity cycle[e.g. Rowse and Roxburgh, 1983; Bravo and Stewart, 1994].
Diego et al. (JGR, 2009) performed an alghoritm to evaluate the CH persistence by analysing
a century of corotating perturbations effect on geomagnetic activity.
The Persistence index computed during descending phases shows a high anti-correlation
with the following solar activity cycle amplitude.
Global Sunspot’s Areas for solar cycle n. 24 has been predicted to be the lowest of the
last 100 years!
Range of V is nearly constant
from 0.3 to1 A.U.
Ratio between average
values of Helios and OMNI
data (H/O) is:
H/O(Vtot) = 1.0
H/O(VHSS) = 1.0
H/O(VMC) = 0.9
H/O(VNCDE) = 0.9
Transient Perturbations
show lower values (200-280
km/s) not fount at 1 A.U.
Range of D is near 10 times
higher at Mercury’s orbit
Ratio between average
values of Helios and OMNI
data (H/O) is:
H/O(Dtot) = 9.2
H/O(DHSS) = 10.2
H/O(DMC) = 11.6
H/O(DNCDE) = 8.8
Relative position of different
classes of perturbation
remains the same
Range of T is near 2 times
higher at Mercury’s orbit
Ratios between averaged
values of Helios and OMNI
data (H/O) is:
H/O(Ttot) = 2.0
H/O(THSS) = 1.9
H/O(TMC) = 1.5
H/O(TNCDE) = 1.9
Relative position of different
classes of perturbation
remains the same
Range of B is nearly 4 times
higher at Mercury’s orbit
Ratios between averaged
values:
H/O(Btot) = 5.0
H/O(BHSS) = 6.3
H/O(BMC) = 3.6
H/O(BNCDE) = 4.8
In the inner heliosphere HSSs
have IMF B values.
comparable to transient’s
ones.
The radial gradient is greater
of about a factor 2 for HSS
with respect to transients
(according to Burlaga’s (2001)
global range of variability 3-6)
Range of Bx is nearly 6 times
higher at Mercury’s orbit
Ratios between averaged
values :
For positive values:
H/O(Bxtot) = 7.0
H/O(BxHSS) = 8.1
H/O(BxMC) = 5.4
H/O(BxNCDE) = 6.1
For negative values:
H/O(Bxtot) = 7.6
H/O(BxHSS) = 9.9
H/O(BxMC) = 5.4
H/O(BxNCDE) = 7.0
Results in agreement with
Parker.
The Bx of HSSs has the same
behavior as B
Range of By is nearly 3 times
higher at Mercury’s orbit
Ratios between Ranges:
H/O(Bytot) = 2.9
H/O(ByHSS) = 4.1
H/O(ByMC) = 2.4
H/O(ByNCDE) = 3.2
Results in agreement with
Parker.
Contributions on Alfvenic
fluctuations during HSSs
enlarge the range at
Mercury’s orbit (Korth et al.,
2011, Diego et al.2005)
Range of Bz is near 4 times
higher at Mercury’s orbit
Ratios between Ranges:
H/O(Bztot) = 3.7
H/O(BzHSS) = 4.2
H/O(BzMC) = 3.1
H/O(BzNCDE) = 4.3
Results show radial decrease
≈ 1/r and a ratio Bz/By ≈ 0.6
In agreement with Mariani
et al. (1979)
Helios Data between 0.3 and 0.47 A.U.
Average values
Parker
B (nT) BxPos (nT) BxNeg (nT) By (nT) Bz (nT) D (cm-3) T (K) V (km/s) Spiral
(deg)
Total
33.7
23.8
-24.4
0.7
0.3
68.9
242800
417.6
-16.9
Total_std
9.9
10.8
9.8
13.6
10.7
47.5
162700
120.6
27.3
HSSs
35.3
26.6
-26.7
1.2
0.8
37.9
383258
541.8
-15.2
HSSs_std
7.6
8.2
8.9
11.6
8
15.9
163200
114
21.02
MCs
32.8
21.2
-19.9
-1.8
0.6
111.7
145023
337.6
-17.4
MCs_std
12.3
11.6
9.4
16.3
14.6
44.1
91030
49.1
35
NCDEs
30.5
19.4
-21.7
0.4
0.4
99.4
149800
338.3
-19.6
NCDEs_std 11.2
10.8
11.4
14.4
11.3
48.7
105300
61.7
32.8
Average values of Total dataset are in agreement with previous works (e.g. Burlaga 2001
and reference therein).
Ratios between Helios and OMNI.
Parker
By (nT) Bz (nT)
B (nT) BxPos (nT) BxNeg (nT)
D (cm-3) T (K) V (km/s) Spiral
(*)
(*)
(deg)
Total
5.0
7.0
7.6
3.5
-10.0
9.2
2.0
1.0
0.8
Total_std
3.2
5.4
4.7
2.9
3.7
8.5
1.6
1.2
0.6
HSSs
6.3
8.1
9.9
-1.2
-13.3
10.2
1.9
1.0
0.7
HSSs_std
5.1
4.8
5.9
4.1
4.2
9.4
1.6
1.3
0.5
MCs
3.6
5.4
5.4
-2.0
-12.0
11.6
1.5
0.9
0.5
MCs_std
3.2
4.5
4.1
2.4
3.1
7.0
1.0
0.7
0.7
NCDEs
4.8
6.1
7.0
-1.0
2.0
8.8
1.9
0.9
1.1
NCDEs_std 3.6
5.7
5.7
3.2
4.3
6.0
1.0
0.9
0.7
(*) Average values of OMNI data close to zero
z
y
x
x
HSSs Positive
Magnetospheric Model – Toffoletto Hill modified by Massetti
Empirical–analytical magnetospheric model starting from the Toffoletto–Hill TH93
Code (Toffoletto and Hill, 1989, 1993). The new model has been fine tuned to
approximately match the Mariner10 data (flyby III), and to reproduce some of the
key features of the self-consistent hybrid model of Kallio and Janhunen (2003).
IMF BX component in the model contributes to depict a realistic IMF–magnetosphere
Reconnection geometry.
Dipole values used is computed by Anderson et al, (2011) as 195 ± 10 nT/RM3
HSSs Negative
Sketch of the Mercury’s magnetosphere, computed for different values of IMF
components , showing the spatial distribution of the field lines, which are:
• open on the dayside (XGSM≥-1), (red)
• open on the tail (XGSM<-1), (grey).
• closed (blue).
z
y
MC Positive
x
z
x
y
MC negative
x
x
z
y
NCDE Positive
x
z
x
y
NCDE Negative
x
x
Courtesy of V. Mangano (IAPS-INAF)
Intensity emission (kiloRayleigh) of the D2 line of Na (brightest sodium line).
White profile evidences the planet position (dotted meridian are for the region not illuminated
by the Sun). On the left a double spot probably due to IMF component sudden variations. On
the right a single spots as in the case of defined IMF polarity.
The input is a HSS the magnetic configuration could last for several days.
Suprathermal Particles
SEP dependence on solar activity has been extensively investigated (e.g. Nymmik, 1999,
Storini et al. 2008) and many computational model has been performed (see Vainio et
al. for a review).
Part of their database is summarized in figure above (Laurenza et al. 2007).
Peak flux upper limit at 1 A.U. is close to 105 pfu on hourly averaged data.
28 April 1978 SEP event is one of identified magnetically
connected events (Gardini et al. (2011) for a list)
Helios 1 and 2, and IMP 8 magnetically
connected within 20°; separated of 0.7
A.U. in radial distance.
Proton fluxes recorded in the energy range 4−40 MeV by Helios 1, Helios 2,
IMP 8 spacecraft during 1974−1982 are used to analyze all SEP events for
which at least two spacecraft have their nominal magnetic footpoint within
20◦ in heliocentric longitude from each other.
Radial dependence ~ R
α = 2.13
r = 0.99
The upper limit of Peak Fluxes at
0.3 A.U. is ≈ 106 pfu
(for >10 MeV proton energy)
Summary
• Helios 1 and 2 data for 1975-1980 have been used to evaluate the space
environment between 0.3 and 0.47 A.U. in the most similar condition s for
BepiColombo mission.
• Statistical features for different classes of perturbations have been
compared between Mercury’s and Earth’s orbits
• Relative occurrence s of corotating and transient perturbations have been
studied in relation to long term solar variability and its predictability.
• Response of Mercury’s Magnetosphere for different SW inputs are
displayed to identify field lines connected to external environment
• Suprathermal particles fluxes data for two solar activity cycles have been
used to evaluate occurrence, peaks and fluences at Earth’s orbit.
• The same parameters (upper limit) can be inferred at Mercury’s orbit by
using the radial gradient computed with Helios and IMP8 data.