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

Reconstruction of the solar UV output since 1955 T. Dudok de Wit, M. Kretzschmar LPC2E, CNRS/University of Orléans

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 ? Space Climate 2019 2

Existing UV reconstructions Using solar irradiance models : e.g. NRLSSI2, SATIRE, … Using solar CaK images 
 [Bertello et al., 2010, Chatzistergos’ talk] 
 Using geomagnetic data 
 1.0 a S M D UACs (aromatic/OH) [Svalgaard, 2016] 0.8 0.6 0.4 0.2 16.90 b 1.0 UV-B irradiance (W/m 2 ) Using pollen 
 16.88 a S M D UACs (aromatic/OH) 16.86 0.8 [Jardine et al., 2016] 16.84 0.6 16.82 0.4 16.80 16.78 0.2 16.90 1300 1400 1500 1600 1700 1800 1900 2000 b Space Climate 2019 UV-B irradiance (W/m 2 ) 3 16.88 Calendar years CE 16.86 16.84 16.82 16.80 16.78 1300 1400 1500 1600 1700 1800 1900 2000 Calendar years CE

Challenge Are there other UV proxies that are accurate enough ? stable in time ? Space Climate 2019 4

Challenge Any there any other UV proxies that are accurate enough ? stable in time ? Yes !!! Nobeyema radio polarimeters 10.7 cm radio fl ux (Ottawa/Penticton) : 
 since 1947 3.2, 8.0, 15, 30 cm radio fl ux 
 (Toyokawa/Nobeyama) : since 1950’s 
 http://spaceweather.cls.fr Space Climate 2019 5

Solar radio fl uxes Excellent radiometric stability : < 0.4 sfu/year Space Climate 2019 6

Connection between radio and UV ? The connection between UV irradiance and radio fl uxes is at best indirect (several mechanisms, optical thickness, geometrical e ff ects, …) 
 [White et al., 2011] gyro-synchrotron emissions ➞ major sunspots ➞ sunspots gyro-resonance emissions ➞ plages, coronal loops Bremsstrahlung 1 3 10 30 100 wavelength [cm] Space Climate 2019 7


 
 
 
 
 
 
 Solar variability Interpreting the total radio fl ux in terms of UV output is di ffi cult 
 6-month averages, rescaled Let's focus instead on the rotational variability = contributions from solar structures only Space Climate 2019 8

Example : Halloween event Rotational variability during halloween event (Oct. 2003) Halloween event Space Climate 2019 9

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 <latexit sha1_base64="98qfe5PA6bE4bozeoY1Z7HisUQ=">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</latexit> Blind source separation The radio fl uxes at 5 wavelengths are very redundant 
 Determine their main contributions by using Bayesian blind source separation 
 Assume 
 N X I ( t, λ ) = S k ( λ ) A k ( t ) S k ( λ ) ≥ 0 A k ( t ) ≥ 0 k =1 How many contributions N = ? Space Climate 2019 10

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] ––o–– S 1 mostly short wavelengths 
 (“Gyro-synchrotron emissions”) ––o–– S 2 mostly intermediate wavelengths (“Gyro-resonance emissions”) ––o–– S 3 mostly long wavelengths (“Thermal/Bremsstrahlung”) Space Climate 2019 11

Interpretation of the contributions Amplitude of each contribution Space Climate 2019 12

Interpretation of the contributions Amplitude of each contribution MgII index Conclusion : the long-wavelength contribution S 3 is a proxy for the UV rotational variability Space Climate 2019 13

Interpretation of the contributions Conclusion : the intermediate-wavelength contribution S 2 is a proxy for the sunspot area Space Climate 2019 14


 
 
 Reasoning in 4 steps Consider the rotational variability of the solar radio fl ux 
 This rotational variability re fl ects 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 ????? Space Climate 2019 15


 
 
 
 
 
 
 
 
 
 Long-term changes Consider 6-year averages (1/2 solar cycle) 
 S 3 proxy for UV output S 2 proxy for sunspot area Conclusion the S 2 /S 3 (“spot-to-facula”) ratio has drifted considerably 
 [see also Foukal, 2012] Space Climate 2019 16

Long-term changes Conclusion : before the satellite era, the long-wavelength contribution signi fi cantly deviates from what spectral irradiance models give Space Climate 2019 17


 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 signi fi cantly di ff erent from what irradiance models suggest. 
 Nobeyama centimetric radio observations will stop in ~2021 Space Climate 2019 18

Long-term changes Comparison between long-wavelength contribution S 3 and solar UV proxies Space Climate 2019 20

Long-term changes Conclusion : variations in the intermediate-wavelength contribution S 2 are in full agreement with the sunspot area (and sunspot number) Space Climate 2019 21

Long-term changes Conclusion : the short-wavelength contribution S 1 is highly intermittent and has a distinct long-term evolution Space Climate 2019 22