Andrzej Fludra Algorithm for automatic detection of coronal dimming as a tool for predicting CME’s Danielle Bewsher & Richard Harrison Presented by Andrzej Fludra

Danielle Bewsher & Richard Harrison Introduction CME related coronal (x-ray) dimming first seen with Skylab –Rust & Hildner, 1976; Rust, 1983 Also observed with –Yohkoh e.g Watanabe et al., 1992; Sterling & Hudson, 1997; Gopalswamy & Hanaoka, 1998 –EIT e.g Zarro et al., 1999 –CDS Only detailed spectral analysis e.g Harrison & Lyons, 2000; Harrison et al., 2003 If dimming identifies low coronal source –Analyse source plasma before onset –Possibility of CME prediction?

Danielle Bewsher & Richard Harrison CME Prediction Can we predict a CME onset –No of pixels with decrease in intensity –Using different emission lines If successful at limb, then extend to disk. Basic scheme –Scan Mg IX and Fe XVI EJECT mosaics –1996 to 2005: 178 datasets suitable for use –Automated procedure. If contiguous set of pixels (predefined minimum number) Show decrease in intensity beyond specified limit Define a CME alarm. Compare alarms CME lists –CACTUS

Danielle Bewsher & Richard Harrison CDS Observations EJECT studies started mid-1996 –JOP67 Mosaic of three 4 arcmin fields Exposure: 10 s 4 x 240 arcsec slit (60 locations) Cadence: 50 min Six emission lines: –He I 584 Å (20,000 K) –O V 629 Å (250,000 K) –Mg IX 368 Å (1 million K) –Fe XVI 360 Å (2 million K) –Si X 347/356 Å (1.3 million K) Trade off –Cadence –Plasma diagnostic tools Plasma diagnostics of CME source –Only CDS can do

Danielle Bewsher & Richard Harrison Classic Dimming Example

Danielle Bewsher & Richard Harrison CME Prediction Algorithm Prep/calibrate data Remove background –Assume constant background in space –Variable in time and wavelength Make mosaics from individual rasters Make fixed difference dataset –Reference for fixed difference Find pixels where fixed difference is significant –If abs(difference) > statistical error Block out pixels on disk Group pixels with dimming together space and time –Any of 8 surrounding pixels in space –Same pixels at t - 1 and t + 1 Group neglected if –Number of pixels in group < 1% of pixels in space-time volume

Danielle Bewsher & Richard Harrison Checking CME Prediction IF significant dimming observed in CDS –in enough pixels in space-time volume –in either Mg IX OR Fe XVI –THEN raise alarm Check against CME list –CACTUS (ROB, automated) IF CME identified in list –same time range (±1 hour) –same position range (±10°) AND CDS alarm has been raised THEN –Successful alarm

Danielle Bewsher & Richard Harrison Mg IX data

Danielle Bewsher & Richard Harrison Mg IX fixed difference

Danielle Bewsher & Richard Harrison Mg IX Significant Dimming

Danielle Bewsher & Richard Harrison Comparison

Danielle Bewsher & Richard Harrison Results Dimming identified in Mg IX –4% of pixels No dimming identified in Fe XVI CDS alarm raised CACTUS identified CME in same location and time Successful alarm

Danielle Bewsher & Richard Harrison Results Analysing 20 CDS datasets in 2000 –Alarms: 15 –Successful: 10 –False: 5 Better than 50:50! Of the 15 alarms dimming observed in –Only Mg IX: 5 datasets –Only Fe XVI: 3 datasets –Both Mg IX and Fe XVI: 7 datasets Majority of datasets have active region on limb

Danielle Bewsher & Richard Harrison Future Work Extend comparison to CDAW list Do CME lists have every CME? –If CDS raises alarm, but no CME in list, check LASCO data? Analyse more CDS datasets More development –Reference frame for fixed difference –Criteria for maintaining group –Significance of group dimming –Include disk pixels in analysis –Search CME lists in time range of dimming only, not in time range of whole of CDS observations Watch this space!

Danielle Bewsher & Richard Harrison

Fe XVI Data

Danielle Bewsher & Richard Harrison Fe XVI Fixed Difference

Danielle Bewsher & Richard Harrison Fe XVI Significant Dimming No significant dimming!