response of the thermospheric density to solar euv and ... · the fism (chamberlin et al. 2008),...

Response of the thermospheric density to solar EUV and solar wind forcing

T. Dudok de Wit (University of Orléans) S. Bruinsma (CNES, Toulouse)

Impacts of Intermediate Time Scale SSI Variability 12/2018

Outline

Objective : understand how the thermospheric density responds to solar EUV and to geomagnetic variability

Method: use a transfer function model to gain a better understanding

Motto: learn from what fails

2

What we know


What do we know ?

On time scales ≫ month: variability in the thermospheric neutral density is primarily driven by solar EUV forcing

4

Emmert et al. GRL (2010)

log(density) @ 400 km

solar EUV flux (f10.7 index)

Emmert et al. GRL (2008)


What do we know ?

On time scales < few months: variability is primarily driven by geomagnetic activity (storms), solar EUV + flares

5


What do we know ?

On time scales < few months: variability is primarily driven by geomagnetic activity (storms), solar EUV + flares

6

density @ 800 km

30 cm radio flux (F30)

Ap index

0

10

20

(t)

[10-1

4 k

g m

-3]

density

0

50

100

150

Ap

Ap

2001 2002 200350

100

150

F3

0 [

sfu

]

F30


What do we know ?

On time scales < day (discarded here): highly variable impact of solar flares and geomagnetic storms

7

Qian & Solomon, SSR (2012)

Thermospheric Density: An Overview of Temporal and Spatial

Fig. 1 Neutral density responses to an X17 flare occurred on October 28, 2003 and an X28 flare occurredon November 4, 2003. (a) Neutral density observed by CHAMP on October 28, 2003. The solar local timeof CHAMP orbit was ∼13:10. (b) Neutral density observed by CHAMP on November, 2003. The solarlocal time of CHAMP orbit was ∼12:45. (c) Neutral density simulated by TIE-GCM for October 28, 2003,sampled along the CHAMP orbit. FISM flare spectra were used as solar input for the TIE-GCM. (d) Neutraldensity simulated by TIE-GCM for November, 2003, sampled along the CHAMP orbit. FISM flare spectrawere used as solar input for the TIE-GCM; (c) GOES 0.1–0.8 nm solar irradiance and geomagnetic Kp indexfor October 28, 2003. (d) GOES 0.1–0.8 nm solar irradiance and geomagnetic Kp index for November 4,2003

1974; Davies 1990; Mendillo et al. 1974; Zhang et al. 2005; Tsurutani et al. 2006), withrelatively sparse research concerning the thermosphere (Sutton et al. 2005; Liu et al. 2007a;Pawlowski and Ridley 2008). The thermosphere, with its large mass and high heat capac-ity, is expected to be slower in responding to transient events such as solar flares. How-ever, model simulations and observations show significant rapid density response to solarflares.

Figure 1a and 1b show neutral density at 400 km observed by the CHAMP satellite alongits day-time orbit, for October 28, 2003, and November 4, 2003. Figure 1c and 1d are neutraldensity simulated by the TIE-GCM. Input flare spectra for the TIE-GCM were provided bythe FISM (Chamberlin et al. 2008), which is based largely on data from TIMED/SEE andthe X-ray monitors on the GOES satellites. TIE-GCM density was sampled along CHAMPorbits for comparison to the measured density. Figure 1e and 1f show solar flux in the wave-length range 0.1–0.8 nm measured by GOES 10, and geomagnetic Kp index. An X17 flare

soft X-ray flux

Thermospheric Density: An Overview of Temporal and Spatial

Fig. 1 Neutral density responses to an X17 flare occurred on October 28, 2003 and an X28 flare occurredon November 4, 2003. (a) Neutral density observed by CHAMP on October 28, 2003. The solar local timeof CHAMP orbit was ∼13:10. (b) Neutral density observed by CHAMP on November, 2003. The solarlocal time of CHAMP orbit was ∼12:45. (c) Neutral density simulated by TIE-GCM for October 28, 2003,sampled along the CHAMP orbit. FISM flare spectra were used as solar input for the TIE-GCM. (d) Neutraldensity simulated by TIE-GCM for November, 2003, sampled along the CHAMP orbit. FISM flare spectrawere used as solar input for the TIE-GCM; (c) GOES 0.1–0.8 nm solar irradiance and geomagnetic Kp indexfor October 28, 2003. (d) GOES 0.1–0.8 nm solar irradiance and geomagnetic Kp index for November 4,2003

1974; Davies 1990; Mendillo et al. 1974; Zhang et al. 2005; Tsurutani et al. 2006), withrelatively sparse research concerning the thermosphere (Sutton et al. 2005; Liu et al. 2007a;Pawlowski and Ridley 2008). The thermosphere, with its large mass and high heat capac-ity, is expected to be slower in responding to transient events such as solar flares. How-ever, model simulations and observations show significant rapid density response to solarflares.

Figure 1a and 1b show neutral density at 400 km observed by the CHAMP satellite alongits day-time orbit, for October 28, 2003, and November 4, 2003. Figure 1c and 1d are neutraldensity simulated by the TIE-GCM. Input flare spectra for the TIE-GCM were provided bythe FISM (Chamberlin et al. 2008), which is based largely on data from TIMED/SEE andthe X-ray monitors on the GOES satellites. TIE-GCM density was sampled along CHAMPorbits for comparison to the measured density. Figure 1e and 1f show solar flux in the wave-length range 0.1–0.8 nm measured by GOES 10, and geomagnetic Kp index. An X17 flare

measured density

soft X-ray flux


Forcings

2 external forcings

Solar radiative forcing in the EUV

daily-yearly variations, impulsive bursts during flares only

Joule heating due to geomagnetic activity

highly variable in time

2 internal forcings

Dynamical coupling with the mesosphere below

wave activity: energy and momentum exchange

Infrared cooling by trace gases continuous, caused by greenhouse gases (CO2, CH4, …)

8

strong effect

strong but highly intermittent

weak and poorly known

weak with slow trend


Open questions

1. How exactly does the thermosphere respond to external forcings (linearity, characteristic time scales, etc.) ? This response is not instantaneous (convolutive)

2. What are the best solar EUV proxies ? Is it possible to use one single solar proxy ?

3. What are the best geomagnetic proxies ? Is it possible to use one single geomagnetic proxy ?

9


Major problem

Very few cases when one ONLY of solar/geomagnetic forcing is active

10

How can we study the effect of one forcing, while ignoring the other ?

0

10

20

(t)

[10-1

4 k

g m

-3]

density

0

50

100

150

Ap

Ap

2001 2002 200350

100

150

F3

0 [

sfu

]

F30


2 strategies

11

model with physical assumptions

(MSIS, DTM, …)

tune

solar input

geomagnetic input

density


2 strategies

12

model with physical assumptions

(MSIS, DTM, …)

tune

tune

empirical model (transfer function) density

solar input

solar input

geomagnetic input

geomagnetic input

density

Data and pre-processing


Data

Data: orbit-averaged daily density at 800 km from STELLA (1993-2010)

Geomagnetic proxies: Am, Ap, etc.

Solar proxies: Mg index, F10.7, F30, etc.

14


Pre-processing

Separate the observations into 2 time scales:

Baseline = long-term variations (> 1 month) mostly solar forcing + seasonal variations

Difference = short-term variations (< 1 month) solar and geomagnetic forcing

15

Dudok de Wit & Bruinsma, GRL (2011)

ρ(t)

[10−

14 k

g m−3

]

Apr02 Jul02 Oct02 Jan03 Apr03 Jul030

2

4

6

8

10densitysmoothing (30 days)baselineAp/50

Baseline is more resilient to geomagnetic storms and

to flares


Pre-processing

Long-term variations (baseline) are well modelled by a nonlinear response of the density to the EUV

16

40 60 80 100 120 140

F30 [sfu]

0

1

2

3

4

5

[1

0-1

4 k

g m

-3]

STELLA monthly values of baseline

baseline of EUV flux

base

line

of d

ensit

y


Transfer function model

Model the short-term variability (< 1 month) assuming the response of the density is linear and time-invariant

17




Consider an Output Error (OE) model

18

density geomagne,cindex EUVflux modelerror

⇢[t] =B1(z�1)

F1(z�1)u1[t] +

B2(z�1)

F2(z�1)u2[t] + ✏[t]

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Consider an Output Error (OE) modelusing the Z transform

19

density geomagne,cindex EUVflux modelerror

B(z�1)u[t] = b0u[t] + b1z�1u[t] + b2z

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= b0u[t] + b1u[t� 1] + b2u[t� 2] + . . .<latexit sha1_base64="9L+gb3hxhHf6oH82I/GAdzeZYiA=">AAADYXicjVJNaxRBEH2740eyRt3EYy6NiyCIYWYJ6EUNePEYwU0Cm2WZme3EJvNFT09iGPI7/DVe9Td49qI3f4KvayeghqA9TPerV/Wquro7qTJTuzD82usHN27eur2yOrizdvfe/eH6xl5dNjbVk7TMSnuQxLXOTKEnzrhMH1RWx3mS6f3k5LX3759qW5uyeOfOKz3L4+PCHJk0dqTmw+iFUsk8VKqZupl6QhwJfhotrbEYY28cZovS1Wo+HIVboQx1FUQdGL36CRm75XpvDYdYoESKBjk0CjjiDDFqflNECFGRm6ElZ4mM+DUuMKC2YZRmREz2hPMxrWnHFrR9zlrUKatk/C2VCo+oKRlniX01Jf5GMnv2utyt5PR7O+eadLlysg7vyf5Ldxn5vzrfi8MRnksPhj1Vwvju0i5LI6fid65+68oxQ0XO4wX9ljgV5eU5K9HU0rs/21j83yXSs95Ou9gGP7pdWmE0zuTEcumhYIVWbvJCVl/lA2dLbyvs9bfVkjP0FJwdVb6nAQZ8S9HfL+cq2BtvRcRvt0c7L5ePCivYxEM85st5hh28wS4mrPYRn/AZX/rfgtVgGGwsQ/u9TvMAf4xg8xd6XLIw</latexit><latexit sha1_base64="9L+gb3hxhHf6oH82I/GAdzeZYiA=">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</latexit><latexit sha1_base64="9L+gb3hxhHf6oH82I/GAdzeZYiA=">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</latexit><latexit sha1_base64="9L+gb3hxhHf6oH82I/GAdzeZYiA=">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</latexit><latexit sha1_base64="q9b/n3t31xxvFbrAMPgqMOBla70=">AAADYXicjVJNb9NAEH2J+WhDgbQ99rIiQkJCVHYS4vZAqcSFY5FIWymNItvZFquObdlroLL6O/g1XOE3cOYCN34CbycuAqEK1vL6zZt5MzvrCfMkLo3rfmm1nRs3b91eWe3cWbt77353feOwzKoi0uMoS7LiOAxKncSpHpvYJPo4L3SwCBN9FJ6/sP6jt7oo4yx9bS5yPV0EZ2l8GkeBITXres+UCmeuUtXETNVjYk/wE29p9cXoW+MkmWemVLNuz912Zam/gdeA3vMfkHWQrbfWcII5MkSosIBGCkOcIEDJZwIPLnJyU9TkCqJY/BqX6FBbMUozIiB7zv2M1qRhU9o2ZynqiFUSvgWVCg+pyRhXENtqSvyVZLbsdblryWnPdsFv2ORakDV4Q/ZfuqvI/9XZXgxOsSM9xOwpF8Z2FzVZKrkVe3L1W1eGGXJyFs/pL4gjUV7dsxJNKb3buw3E/00iLWvtqImt8L05ZSGMxju5sYX0kLJCLX/yUr62ynvuBb21sNf/rZpcTE/K3VBle+qgI7PkDwdPRzscIX8w2PWHBLv+aDAa/pqlw/62R/xq2NvfWw4VVrCFB3jEyfGxj5c4wJjVPuAjPuFz+6uz6nSdjWVou9VoNvHHcrZ+AqQvspI=</latexit><latexit sha1_base64="ctVNULD7ettKMhXQ+eE+iBuq4Ic=">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</latexit>

⇢[t] =B1(z�1)

F1(z�1)u1[t] +

B2(z�1)

F2(z�1)u2[t] + ✏[t]




Model selection : how many terms in B(z-1) and in F(z-1) ? Typically 2 to 3 only (parcimoniny)

Model validation : train model on one sample and test it on a different one.

Results : model performs well but model error ϵ still contains dynamic noise rather than instrumental one

20

⇢[t] =B1(z�1)

F1(z�1)u1[t] +

B2(z�1)

F2(z�1)u2[t] + ✏[t]


Results


Results

Performance of empirical model is comparable to that of DTM

22

Jan 02 Apr 02 Jul 02 Oct 02 Jan 03 Apr 030

2

4

6

8

10

12

14

[10

-14 k

g m

-3]

observed densityOE modelDTM modelAp / 50

with F10.7


Results


23


2

4

6

8

10

12

14

[10

-14 k

g m

-3]


with F30


Results


24


2

4

6

8

10

12

14

[10

-14 k

g m

-3]


with F30Jan 02 Apr 02 Jul 02 Oct 02 Jan 03 Apr 03

am

plit

ude [arb

. units

]

SEMMgIISSNF10.7F30GyroBrem


Impulse response

Impulse response = how would the density respond to a one-day unit increase in either solar or geomagnetic forcing

25


Impulse response = how would the density respond to a one-day unit increase in either solar or geomagnetic forcing

Impulse response

26

-5 0 5 10

time [days]

-2

0

2

4

6

8

10

12

14

16

imp

uls

e r

esp

on

se o

f d

en

sity

10-3 response to Ap

-5 0 5 10

time [days]

-2

0

2

4

6

8

10

12

14

16

imp

uls

e r

esp

on

se o

f d

en

sity

10-3 response to F30

Overshoot and rapid relaxation

Slow relaxation, partly non-causal

1σ confidence interval


Conclusions (1/2)

Empirical model offers better reconstruction than existing (DTM, JB2006, ...) models ➞ 20-30% error reduction

No need to distinguish periods during which one type of forcing only is active ➞ better statistics

Allows to test different solar proxies for orbit specification

27


Conclusions (2/2)

Most appropriate solar EUV proxy is the 30 cm radio flux (F30)(rather than F10.7 or MgII index)

Response on time scales < 1 month EUV forcing: response is remarkably linear

geomagnetic activity: mostly linear response

Recovery time for geomagnetic forcing is < 1 day = faster than the resolution of our data (beware)

Learn from what does not (yet) work

28

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�⇢

⇢/ Ap+

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response of the thermospheric density to solar euv and ... · the fism (chamberlin et al. 2008),...

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