1. Nicholeen Viall & James Klimchuk NASA GSFC
A Survey of Nanoflare Properties in Active Regions Observed with the Solar Dynamics Observatory
Nicholeen Viall & James Klimchuk
NASA GSFC

2. Timelag Measures Thermal Evolution of Plasma
Δt, Time Lag between 335 Å and 211 Å
Cooling time from
335 Å (~3 MK) to 211 Å (~2 MK)
131 Å
EBTEL SDO/AIA light curves
Time Offset (s)
Time lag method of Viall & Klimchuk 2012 cross correlates lightcurves in different AIA channels
Cross correlate two wavelengths at different temporal offsets: peak cross correlation = time lag between light curves
Key: in a nanoflare the heating is invisible, and slow cooling dominates all coronal emission
Method identifies nanoflares in coronal loops AND diffuse emission between (Viall & Klimchuk 2013)
Thermal Ev olution We allow for slow heating too

3. Nanoflare Time Lag Map SDO/AIA 171
(~3 MK-~2 MK)
0.8 MK
Apply test on pixel-by-pixel basis to 12-hr timeseries
Almost exclusively positive time lags and transition region
Not just at a few discrete loops, but everywhere
Persistent pattern of cooling throughout active region
Perform time lag test at every pixel and tag that pixel with the time lag; create time lag maps; here is one pair of channels
Positive time lags: cooling
Negative time lags: slow heating
zero time delay: transition region/moss

4. WWB2012 studied 15 AR, showed that DEM is a function of total unsigned magnetic flux of the AR. While VK2012 DEM was consistent with low frequency nanoflares, many AR’s DEMs consistent with steady heating, and not with impulsive nanoflares that fully cool

5. 335Å Å (3 MK-2 MK)
VK2012 AR
First 5 time lag maps, the pair
Red/orange/yellow = post-nanoflare cooling

6. 335Å Å (3 MK-2 MK)
Red/orange/yellow = post-nanoflare cooling

7. 335Å Å (3 MK-2 MK)
Red/orange/yellow = post-nanoflare cooling

8. Not just a few loops; rather, entire AR cools
All 15 Time Lag Maps
VK2012 AR
Only showing you one channel pair for brevity but also because other pairs are the key to reconciling this seeming discrepency
Cooling patterns as in original study persist throughout every single AR
Not just a few loops; rather, entire AR cools

9. All 15 Time Lag Maps
VK2012 AR
Only showing you one channel pair for brevity but also because other pairs are the key to reconciling this seeming discrepency
Cooling patterns as in original study persist throughout every single AR… *between Å*
Controversy!

10. Three of the steepest DEM slope/most consistent with high frequency nanoflares in different channel pairs
Look at other channel pairs to see full evolution of plasma
All three AR emit in hot component of 94 Å and are in a state of cooling
Nov 8 has full cooling; others do not
Maps reveal non-uniform behavior: Dynamics in box may not represent entire AR

11. Medium Frequency Nanoflare Trains Reproduce Zero Time Lags in Core; Full Cooling Cannot
2-hr
12-hr
Bradshaw & Viall 2016

12. Cooling Truncates (i.e. Plasma is reheated) around ~ 1 MK for all ARs

13. Conclusions
Cooling is everywhere: We analyzed the 15 AR of Warren, Winebarger & Brooks 2012 and found widespread cooling in all of them. The results are consistent with impulsive nanoflare heating followed by slower cooling
Its partial cooling: Only occasionally, however, is there full cooling from above 7 MK to well below 1 MK. More often the plasma cools to approximately 1-2 MK before being reheated by another nanoflare
Distributions of medium frequencies: Distributions of medium frequency nanoflares with the average delay between successive events on an individual flux tube being comparable to the plasma cooling timescale are consistent with all 15 ARs EM slopes AND time lags (e.g. Cargill 2014; Cargill, Warren & Bradshaw 2015; Bradshaw & Viall 2016)