The EUV spectral irradiance of the Sunfrom 1997 to date

Giulio Del ZannaPPARC/STFC Adv. Fellow

DAMTP, CMS, University of Cambridge

Vincenzo AndrettaOAC INAF, Italy

Tom Woods, Phil Chamberlin et al., LASP, Univ. of Colorado, USA

(Del Zanna et al. 2005,2006, 2009)

G. Del Zanna - UKSP/NAM/JENAM 2009

Key questions1. What is the EUV spectral irradiance and how it varies? 2. Can we model it ?3. Does it affect our climate?

X-ray -- 3-5 MKEUV -- 1 MK

SOHO TRACE Yohkoh

The total irradiance is one of the main drivers for global climate.

Variability exists but is small (0.2%) and insufficient to explain

variations on global weather.

"Winter Scene with Frozen Canal" by Aert van der Neer

G. Del Zanna - UKSP/NAM/JENAM 2009

Why study UV and EUV ?

UV radiation could be a significant driver for terrestrial climate (e.g. Haigh 1996).The EUV radiation creates the ionosphere and might also have an indirect effect.Spectral irradiance measurements:plenty in UV, almost none in X-rays and EUV (until TIMED 2002)

EUV irradiancesNASA TIMED/SEE

UV irradiances

Woods & Eparvier (2006)Source: LASP, Univ. of Colorado)

CALIBRATION CALIBRATION CALIBRATION

G. Del Zanna - UKSP/NAM/JENAM 2009

CDS NIS

G. Del Zanna - UKSP/NAM/JENAM 2009

He I, O V (0.25), Mg X (1 MK), Fe XVI (2.5 MK)

SOHO CDS NIS: 1000 exposures sampling the whole Sun in 13 hours

`Del Zanna minimum’ ?

G. Del Zanna - UKSP/NAM/JENAM 2009

SDO EVE prototype‘It could take a lifetime to understand such a spectrum’ (P.J.Storey, UCL)

Woods et al. (GRL, 2009)Chamberlin et al. (GRL, 2009)

G. Del Zanna - UKSP/NAM/JENAM 2009

SOHO NIS irradiances vs. EVE prototypeSDO/EVE

G. Del Zanna - UKSP/NAM/JENAM 2009

CDS NIS irradiances

G. Del Zanna - UKSP/NAM/JENAM 2009

Summary and further work SDO EVE vs. NIS radiances

The irradiances in lines formed in the low transition region have changed little (max 50%) over the last 12 years (also from late 60’s).

At 1 MK by a factor of 5 and at 2.5 MK by a factor of 40.

Further work:- Explain the Sun-as-a-Star and other stars in XUV with

radiance measurements. - Improve predictions of EUV radiances and irradiances

(current models use proxies: does not work!): - climate models - back in time. thank you

B2/