Solar Soft X-ray
Variability During the
SORCE Mission
Tom Woods and Gary Rottman
LASP / University of Colorado
tom.woods @lasp.colorado.edu
gary.rottman @lasp.colorado.edu
SORCE Science Meeting - Dec 2003
Woods - SORCE XPS Results -Page
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Outline
♦ SORCE XUV Photometer System (XPS) Summary
− Instrument overview
− Data products
− Example time series
♦ Moderate Solar Cycle Activity During the SORCE Mission
♦ Solar Rotation (27-day) Variations
♦ Over 150 Solar Flares Observed
− May-July 2003 solar storm period
− October-November 2003 solar storm period
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SORCE XPS Measures the Solar XUV Irradiance
♦ XUV Photometer System (XPS)
XP#
Filter
Band 1
Band 2
1
Ti/C
0.1-7 nm
-
2
Ti/C
0.1-7 nm
-
− 1 Lyman-α (121.6 nm) photometer
3
Al/Sc/C
0.1-3 nm
17-23 nm
− 3 bare (Vis) Si photodiodes
4
Bare
Vis
-
5
Al/Nb/C
0.1-3 nm
17-21 nm
6
Ti/Mo/Au
0.1-11 nm
7
Ti/Mo/Si
0.1-3 nm
11-17 nm
8
Bare
Vis
-
9
Al/Cr
0.1-7 nm
29-34 nm
10
Al/Mn
0.1-7 nm
25-34 nm
11
Lyman-α
121-122
-
12
Bare
Vis
-
− 8 XUV Si photodiodes (3 calibration)
• 0.1-34 nm with Δλ ~ 7 nm
• measure fused silica filter transmission
− 8 position filter wheel
• 1 clear, 2 fused silica filters, 5 blank (dark)
Filter
Wheel
Control
Electronics
SORCE XPS is almost identical to TIMED SEE
XPS that began measurements in January 2002.
SORCE Science Meeting - Dec 2003
Filter
Wheel
(inside
purge
cover)
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Photodiode
Electronics
Section
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SORCE XPS Data Products (Version 4)
♦ XPS Normal Science Observations
− Step through the filter wheel positions with a time cadence of ~5
minutes for solar observations (orbit duty cycle of ~70%)
♦ XPS Level 2 Data Products
− Irradiance for each integration period from the 9 XUV photometers
• Irradiance units in W/m2, wavelength units in nm
− SORCE XPS Level 2 is same as TIMED SEE XPS Level 1
− Merged L2 is the irradiance in 5-minute intervals
♦ XPS Level 3 Data Products
− Irradiance from the 9 XUV photometers averaged over the day and
averaged in 6-hour intervals
− SORCE XPS Level 3 is same as TIMED SEE XPS Level 2
♦ SORCE data are available from GSFC DAAC
− http: //lasp.colorado.edu/sorce/data_access.html
SORCE Science Meeting - Dec 2003
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Example Time Series for SORCE XPS
Level 2 Time Series
Log scale
5-min intervals
Channel 2: 0-7 nm
Level 3 Time Series
6-hour averages
daily average
Channel 2 : 0-7 nm
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Examples of Solar Variations
♦ Solar Cycle - months to years
− Evolution of solar dynamo with 22-year magnetic
cycle, 11-year intensity (sunspot) cycle
Solar Cycle (11-years)
XUV 0-7 nm
H I 121.5 nm
♦ Solar Rotation days to months
Solar Rotation (27-days)
− Beacon effect of active
regions rotating with
the Sun (27-days)
Flares
♦ Flares - seconds to hours
− Related to solar storms (such as
CMEs) due to the interaction of
magnetic fields on Sun
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Solar Activity During the SORCE Mission
♦ Solar cycle activity has
been relatively flat during
2003 but with periods of
large solar storms:
− Flares
− Proton Storms
− Coronal Mass Ejections (CMEs)
♦ SORCE mission began in
solar cycle 23 with solar
moderate conditions
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Solar Rotations Dominate the Solar FUV Irradiance
♦ SORCE has so far observed 10 solar rotations
− Typical solar rotation is ~27 days (lower latitudes rotate faster)
XPS #11
H I Lyman-α
121.6 nm
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Solar Flares Dominate the Solar XUV Irradiance
♦ SORCE XPS has
observed several flares in
2003
− Concentrations of flares are:
• May 26 - June 26, 2003
• Oct. 19 - Nov. 4, 2003
− Monster flares on:
• X17 on Oct. 28
• X28 on Nov. 4
Flare
Type
SORCE
Mission
May 26 June 26
Oct. 19 Nov. 4
Large > x4
30
9
13
Total > 3-σ
195
84
83
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1-σ
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Summary of Solar Flare Effects
♦ Solar flares, which last for minutes to hours, are most obvious for
coronal emissions (wavelengths < 37 nm)
− This flare energy is mostly deposited below 100 km into the mesosphere and
upper stratosphere
− Furthermore, the large flares are often accommodated with solar proton
storms, of which the higher energy protons can reach the ground [e.g.,
Shumilov et al., GRL, 19, 1647, 1992]
♦ The atmosphere responses with rapid ionosphere changes,
temperature increases, and photochemistry changes
− Ionosphere changes disrupt communications (space weather operations)
− Photochemistry affected by these flares include NO and H2O, which in turn
affect the O3 chemistry in the stratosphere [e.g., Midya and Midya, EPM, 61,
175, 1993]
− Extra energy from the flares also cause heating, which in turn changes
reaction rates and changes in the dynamics of the atmosphere [e.g.,
Martynkevich, in Dynamical Processes, 1985]
SORCE Science Meeting - Dec 2003
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October - November 2003 Solar Storm Period
Movie of the Oct-Nov 2003 Solar Storm Period
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Solar Variability from the Large Flares
X17 flare on Oct. 28
X28 flare on Nov. 4
λ Range
Change
λ Range
Change
XUV: 0-10 nm
x 31
XUV: 0-10 nm
x 52
EUV: 30-115 nm
x 1.9
EUV: 30-115 nm
x 1.5
Lyman-α: 121.6 nm
x 1.12
Lyman-α: 121.6 nm
x 1.03
FUV: 115-190 nm
X 1.05
FUV: 115-190 nm
X 1.03
TSI : all λs
Δ 270 ppm
TSI : all λs
none
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Summary
♦ SORCE XPS data products are available
− XPS Version 4 data products are validated and ready for solarterrestrial research
♦ 2003 has been an exciting period for solar irradiance
studies
− Several large solar storms have dominated the solar activity
− The X17 flare on Oct. 28 and the X28 flare on Nov. 4 has
redefined our understanding and expectations for large flares
♦ Future studies
− Categorize the different flare observations
− Study flare impacts on Earth’s atmosphere
• e.g., atmospheric modeling with HAO/NCAR TIME-GCM
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Validation for XPS Irradiances
♦ XUV (0-34 nm) Validation for SORCE XPS
− Initial comparison with TIMED SEE XPS and SORCE XPS showed factor of
~2 lower irradiance for SORCE XPS for some photometers
− Resolved difference using independent (third-type) calibrations in May 2003
with rocket XPS and its flight in August 2003 (for TIMED SEE annual
calibration underflight)
• BESSY & SURF-III & new calibrations agree shortward of 10 nm
• SURF-III & new calibrations agree longward of 10 nm
− None of the XUV channels show any in-flight degradation
♦ Lyman-α Validation for SORCE XPS
− Comparison with TIMED SEE EGS and SORCE SOLSTICE
• Initial comparison showed that SORCE XPS is lower by ~10%
− Attribute to pre-flight degradation for SORCE XPS
• Mission comparison indicates XPS degradation is about 10% per year
♦ Revised XPS Calibrations in Version 4 Data Products
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