Solar extreme ultraviolet (EUV) contributions to the Solar Irradiance Reference Spectrum (SIRS)

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The

Whole

Heliosphere

Interval

(WHI)

was

a

coordinated

effort

with

inputs

from

over

50

models

and

observatories,

both

satellite

and

ground

based,

to

characterize

the

Sun

and

heliosphere

during

solar

minimum

conditions
.

The

time

period

selected

for

this

quiet

Sun

WHI

campaign

was

April

10
-
16
,

2008
.

One

of

the

goals

of

the

solar

minimum

WHI

was

to

produce

a

definitive

Solar

Irradiance

Reference

Spectrum

(SIRS)

for

quiet

Sun

conditions

ranging

in

wavelength

from

0
.
1

nm

up

to

2400

nm
.

During

this

WHI

campaign

on

April

14
,

2008
,

a

sounding

rocket

was

launched

from

White

Sands

Missile

Range

that

observed

the

solar

spectral

irradiance

in

these

solar

minimum

conditions

in

the

extreme

ultraviolet

(EUV)

wavelength

range

from

0
.
1
-
105

nm

as

well

as

Lyman

Alpha
.

The

observations

from

6
.
0
-
106
.
0

nm

that

are

at

0
.
1

nm

spectral

resolution,

which

are

the

source

of

these

wavelengths

for

the

SIRS,

are

shown

as

discussed

here
.



Figure

4
:

SIRS

is

the

combination

of

the

following

measurement
:

Rocket/EVE (1), TIMED/SEE (Figure 2), SORCE/SOLSTICE (panel 2), SORCE/SIM
(panel 3)) from 0.1 to 2400 nm during solar minimum conditions on April 14 2008. Panels
4
-
6 show solar variability between March 2008 and April 2008; values in red indicate
negative variability (sunspot darkening). Panels 7
-
9 show comparison of WHI SIRS to
the Atlas
-
3 reference spectrum obtained in March 1995 [Thuillier et al., 2004]


Rocket EVE SORCE/SOLSTICE SORCE/SIM

Solar extreme ultraviolet (EUV) contributions to the

Solar Irradiance Reference Spectrum (SIRS)

Phillip C. Chamberlin, Thomas N. Woods, Francis G. Eparvier, Juan Fontenla,
Margit Haberreiter,

Gerald Harder, Rachel A. Hock, Martin Snow

LASP, University of Colorado, Boulder, USA

haberreiter@lasp.colorado.edu














Figure

1
:

Comparison

of

the

EVE

rocket

spectrum

observed

April

14
,

2008

at

practically

quiet

Sun

conditions

with

the

EUV

spectrum

calculated

with

the

preliminary

Solar

Radiation

Physical

Model

(SPRM,

Fontenla

et

al
.
,

2009
)
.

The

radiative

transfer

is

solved

in

spherical

symmetry

(e
.
g
.

Mihalas
1978
),

which

yields

realistic

emerging

intensit
ies

for

the

extended

corona
.

We

use

a

set

of

temperature

structures

for

the

chromosphere,

transition

region

and

corona

that

will

enable

us

to

calculate

the

time
-
dependent

spectra

for

different

levels

of

activity
.

For

the

minimum

condition

we

used

the

following

contribution
:

75
%

quiet

Sun,

22
%

network,

3
%

active

network
;

for

details

see

Haberreiter

and

Fontenla,

(
2009
)
.

References:

Chamberlin, P. C., T. N. Woods, D. A. Crotser, F. G. Eparvier, R. A. Hock, and D. L. Woodraska (2009), Solar cycle minimum me
asu
rements of the solar
extreme ultraviolet spectral irradiance on 14 April 2008, Geophys.Res. Lett., 36, L05102, doi:10.1029/2008GL037145.

Chamberlin, J. Harder, M. Snow (2009), Solar Irradiance Reference Spectra (SIRS) for the Whole Heliosphere Interval (WHI). Ge
oph
ys. Res. Lett., 36,
L01101, doi:101029/2008GL036373

Fontenla et al., 2009, Semi
-
empirical Models of the Solar AtmosphereIII. Set of NLTE Models for FUV/EUV Irradiance Computation,
submitted

Haberreiter and Fontenla, 2009, In: Recent Directions in Astrophysical Quantitative Spectroscopy and Radiation Hydrodynamics
AIP

Conference
Proceedings

Mihalas 1978, Stellar Atmospheres

Thuillier, G., L. Floyd, T. N. Woods, R. Cebula, E. Hilsenrath, M. Herse
´
, and D. Labs, 2004, Solar irradiance reference spectra for two solar active levels,
Adv. Space Res., 34, 256 261.

3. EVE rocket spectrum compared to TIMED SEE

Figure

3
:

S
hown

is

the

comparison

of

the

1
nm

binned

EVE

rocket

data

(red
:

MEGS
-
A
1
,

blue
:

MEGS
-
A
2
)

to

the

TIMED

SEE

Version

9
,

Level

3

data

(black

line)

at

similar

1
nm

bins
.

The

differences

between

the

data

sets

are

mainly

attributed

to

TIMED

SEE




Multiple EUV Grating Spectrograph (MEGS)



a
t 0.1 nm resolution:

MEGS
-
A: 5
-
37 nm

MEGS
-
B: 35
-
105 nm
;



at 1 nm resolution:

MEGS
-
SAM: 0
-
7 nm
;



at 10 nm resolution:

MEGS
-
Photometers: @ 122 nm



Ly
-
a Proxy for other H I emissions at 80
-
102 nm and He I emissions at 45
-
58 nm



EUV Spectrophotometer (ESP):


at 4 nm resolution:

17.5, 25.6, 30.4, 36 nm
; at 7 nm resolution:

0
-
7 nm (zeroth order)



In
-
flight calibrations from ESP and

MEGS
-
P

on daily basis and also annual calibration rocket flights

5. The Solar Irradiance Reference Spectrum (SIRS)

4. EVE Instrument Details

2. Coronal Temperature structures

1. Comparison of the EVE rocket spectrum with the synthetic spectrum calculated with SRPM

Figure

2
:

For

the

calculation

of

the

synthetic

EUV

spectrum,

a

set

of

coronal

temperature

structures

is

used

as

input

to

SRPM

to

solve

the

statistical

equation

for

the

level

populations
.

SPRM

accounts

for

app
.

14
,
000

atomic

levels
.

For

the

chromosphere

and

transition

region

we

solve

the

full

non
-
LTE

radiative

transfer

for

ions

up

to

ion

charge

2
.

For

higher

ionization

stages

we

employ

the

optically

thin

approach
.

Combining

the

spectra

for

the

chromosphere,

transition

region

and

corona

leads

to

the

synthetic

spectrum

as

shown

in

Figure

1

(black

line)
.

5
10
4

1
10
5

1.5
10
5

2
10
5

1
10
6

2
10
6

3
10
6

SRPM - Quiet Corona
SRPM - Quiet Coronal Netw.
SRPM - Active Coronal Netw.
SRPM - Active Region I
SRPM - Active Region II
Cranmer - Equatorial Hole
Cranmer - Active Retion
Cranmer - Polar Region
Height (km)
Temperature (K)