Reconstruction of the solar UV output since 1955 T. Dudok de Wit, - - PowerPoint PPT Presentation

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Reconstruction of the solar UV output since 1955 T. Dudok de Wit, - - PowerPoint PPT Presentation

Sep 02, 2022 17 likes •239 views

Reconstruction of the solar UV output since 1955 T. Dudok de Wit, M. Kretzschmar LPC2E, CNRS/University of Orlans Open questions How does the observed solar UV output vary on the long term ? What was its level during the Maunder era ? How

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Reconstruction of the solar UV output since 1955

  • T. Dudok de Wit, M. Kretzschmar

LPC2E, CNRS/University of Orléans

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Space Climate 2019

Open questions

How does the observed solar UV output vary on the long term ? What was its level during the Maunder era ? How was it before the 1990’s ?

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Space Climate 2019

Existing UV reconstructions

Using solar irradiance models : e.g. NRLSSI2, SATIRE, … Using solar CaK images 


[Bertello et al., 2010, Chatzistergos’ talk]


Using geomagnetic data 


[Svalgaard, 2016]

Using pollen 


[Jardine et al., 2016]

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0.2 0.4 0.6 0.8 1.0 UACs (aromatic/OH) 16.78 16.80 16.82 16.84 16.86 16.88 16.90 UV-B irradiance (W/m2) Calendar years CE D M S a b 1300 1900 1800 1700 1600 1500 1400 2000 0.2 0.4 0.6 0.8 1.0 UACs (aromatic/OH) 16.78 16.80 16.82 16.84 16.86 16.88 16.90 UV-B irradiance (W/m2) Calendar years CE D M S a b 1300 1900 1800 1700 1600 1500 1400 2000

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Space Climate 2019

Challenge

Are there other UV proxies that are

accurate enough ? stable in time ?

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Space Climate 2019

Challenge

Any there any other UV proxies that are

accurate enough ? stable in time ?

Yes !!!

10.7 cm radio flux (Ottawa/Penticton) : 
 since 1947 3.2, 8.0, 15, 30 cm radio flux 
 (Toyokawa/Nobeyama) : since 1950’s


http://spaceweather.cls.fr

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Nobeyema radio polarimeters

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Space Climate 2019

Solar radio fluxes

Excellent radiometric stability : < 0.4 sfu/year

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Space Climate 2019

Connection between radio and UV ?

The connection between UV irradiance and radio fluxes is at best indirect (several mechanisms, optical thickness, geometrical effects, …)


[White et al., 2011]

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wavelength [cm] 1 3 10 30 100 gyro-synchrotron emissions gyro-resonance emissions Bremsstrahlung ➞ major sunspots ➞ sunspots ➞ plages, coronal loops

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Space Climate 2019

Solar variability

Interpreting the total radio flux in terms of UV output is difficult
 
 
 
 
 
 
 
 Let's focus instead on the rotational variability = contributions from solar structures only

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6-month averages, rescaled

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Space Climate 2019

Example : Halloween event

Rotational variability during halloween event (Oct. 2003)

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Halloween event

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Space Climate 2019

Blind source separation

The radio fluxes at 5 wavelengths are very redundant
 Determine their main contributions by using Bayesian blind source separation
 
 Assume
 
 
 
 
 How many contributions N = ?

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I(t, λ) =

N

X

k=1

Sk(λ) Ak(t)

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Sk(λ) ≥ 0

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Ak(t) ≥ 0

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Space Climate 2019

Interpretation of the contributions

All the salient features of the rotational variability are captured by 
 3 contributions only (N=3) [Dudok de Wit et a., 2014]

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––o–– S1 mostly short wavelengths
 (“Gyro-synchrotron emissions”) ––o–– S2 mostly intermediate wavelengths (“Gyro-resonance emissions”) ––o–– S3 mostly long wavelengths (“Thermal/Bremsstrahlung”)

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Space Climate 2019

Interpretation of the contributions

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Amplitude of each contribution

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Space Climate 2019

Interpretation of the contributions

Conclusion : the long-wavelength contribution S3 is a proxy for the UV rotational variability

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MgII index Amplitude of each contribution

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Space Climate 2019

Interpretation of the contributions

Conclusion : the intermediate-wavelength contribution S2 is a proxy for the sunspot area

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Space Climate 2019

Reasoning in 4 steps

Consider the rotational variability of the solar radio flux
 
 
 This rotational variability reflects the cycle variability 


[Preminger and Walton 2005, 2006; DdW et al., 2018]


This variability has 3 contributions only, with

long-wavelength contribution = proxy for the UV output intermediate-wavelength contribution = proxy for the sunspot area
 


Did these contributions change since the 1950’s ?????

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Space Climate 2019

Long-term changes

Consider 6-year averages (1/2 solar cycle)
 
 
 
 
 
 
 
 
 
 
 Conclusion the S2/S3 (“spot-to-facula”) ratio has drifted considerably


[see also Foukal, 2012]

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S2 proxy for sunspot area S3 proxy for UV output

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Space Climate 2019

Long-term changes

Conclusion : before the satellite era, the long-wavelength contribution significantly deviates from what spectral irradiance models give

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Space Climate 2019

Final conclusion

A new and stable UV proxy from synoptic solar radio observations
 Agreement with spectral irradiance models (NRLSSI2, SATIRE-TS) goes down before satellite era Warning : long-term changes in the solar UV output may be significantly different from what irradiance models suggest.
 
 Nobeyama centimetric radio observations will stop in ~2021

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Space Climate 2019

Long-term changes

Comparison between long-wavelength contribution S3 and solar UV proxies

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Space Climate 2019

Long-term changes

Conclusion : variations in the intermediate-wavelength contribution S2 are in full agreement with the sunspot area (and sunspot number)

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Space Climate 2019

Long-term changes

Conclusion : the short-wavelength contribution S1 is highly intermittent and has a distinct long-term evolution

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