NADIR MURI Focus Area VI. Forecasting Solar EUV/UV Radiation

1. NADIR MURIFocus Area VI. Forecasting Solar EUV/UV Radiation 2008/10/21 J. Fontenla, M Haberreiter LASP – Univ. of Colorado Juan.Fontenla@lasp.colorado.edu Margit.Haberreiter@lasp.colorado.edu

2. Forecast Goal • Input • Near side: • Solar disk daily images (Ca II K, red continuum) • Other visible and UV images (e.g. EIT, magnetograms) • Far side: • Helioseismic calibrated images (looking though the Sun) • Ly alpha backscattering images (looking around the Sun) • Output: • Daily nowcast (today’s full spectrum at any resolution) • Daily forecasted spectra for the next solar rotation • A spectra for each day • Uncertainty estimates for each of these

3. Lyα Nowcast vs Observations Over the decay of Solar Cycle 23 the PSPT mask-based synthesis gives the correct rotational modulation, but it underestimates the long-term trend. A global component of brightness increase is missing. When good images are available the rotational modulation can be nowcasted very well. We picked a case study in the fall of 2005 to study forecast of rotational modulation variations by combining PSPT-based features masks with SWAN and Helioseismic far-side images.

4. Features Synoptic Mask Obsolescence mask indicates number of days since each pixel was observed by PSPT. 0 or -1 indicates observation on the same day. Features mask show what is (or was) on the solar surface. Three identified regions correspond to active regions that were reported by NOAA with various numbers. The regions near the poles are never well observed. Carrington Latitude Carrington Longitude

5. SWAN Light Curve On a few days around 2005/9/3 a rapid increase is observed in Lyα backscattering around this longitude and then stabilized and slowly decayed. The precise longitude of the responsible solar region is not known and the latitude is completely eliminated in the analysis in order to reduce the noise due to observational issues. On these days this longitude was on the far-side. Only relatively minor variations are found elsewhere; they are complicated and cannot be clearly resolved from these data alone. Carrington Longitude 240 deg

6. Helioseismic Images Far-side helioseismic images show a very large and rapid increase in the signature of SG1 at ~230 deg longitude and ~-10 deg latitude. SG1 increase corresponds to the Lyα backscattering increase. The other regions (SG2 & SG3 are not clearly visible in helioseismic signals. SG1 helioseismic signature increased by ~10 times.

7. Lyα Backscattering Lyα backscattering image. The change in the SWAN far-side images above is consistent with the far-side helioseismic image but is not so well focussed, and there are shadows in the field of view and stars that complicate the interpretation. However, we need an increase of ~2.8 in the SG1 feature areas to explain the observed Lyα increase between 2005/9/1 and 2005/9/4. Changes in SG2 and SG3 are also included and improved the agreement. Thus, we increase SG1 feature areas by ~2.8.

8. Refined Synoptic Mask The poles were filled by standard internetwork and network mix. SG1 features areas were increased by factor 2.8, SG2 areas was increased and SG3 areas were decreased at the rate observed when each of these regions left the visible hemisphere. The increases were set to the expected when these regions become visible again. (The features were replaced by equivalent areas circle and rings.)

9. Upcoming Rotation Forecasted Lyα Just shifting the previous rotation gives bad results at least for the period 2005/9/5-25. The period between minima is several days less than 27 days so we shifted to make the shifted value coincide with the observed on 9/3. Shifting gives bad results and more shift is even worst. The reason for this failure is that several active regions are present and all vary on time, The refined mask predicted the min and rise very well, and also the max amplitude. On 9/17 there is some error but is better than just shifting, and after this the forecast is still good.

10. Comment About SG1 • SG1 came back to the visible disk on 2005/9/7-8 after large growing on the far-side. It was then named as NOAA 10808 and produced several large flares including an X17. • It’s fast growth in a few days and up to a very respectable size may indicate was likely to produce X flares. • If this rapid growth of an active region occurs while in the visible hemisphere, error in the forecast would be introduced. • The only way to avoid this error is to detect the future growth from; perhaps near-side helioseismic data and surface flows can do it.

11. Conclusion • In all cases taking into account the PSPT-based synoptic images, when refined by use of the observed trends in active regions and by considering far-side helioseismic and Lyα data produces a good forecast. • Other methods that implicitly or explicitly assume unchanged features give bad results. • Forecast of Lyα using our methods is possible and fairly accurate for about 2 weeks advance. • In cases of rapid emergence of an active region on the visible hemisphere significant errors may occur.

12. The full spectrum forecast • The same technique applied here to Lyα will be applied to forecasting the entire spectrum in the range 10 to 180 nm (at least) • For this calculations of the radiance spectra for the features are ongoing. See next talk…