Solar Cycle 24 Group G

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Tues (9-Dec-2008)

Contents

Introduction

Calculation show that Hinode/XRT lower limit on energy (with temperature discimination) ~7x10^23 erg (T=2 MK).

Microflares so what

why now?

who cares?

Polar X-ray Jets

Does not matter where in coronal hole you are for where the jets occur (no latitude dependence). Associated with increases in soft x-rays (maybe also observed with RHESSI?). Energy is 1027 erg for these SXR events. Larger polar jet also observed on the coronagraph. Transverse motion from direction of jet is usual. Statistics of jets (about 100 jets)...average duration approx. 800 sec. (as defined by the SXR source), average size 0.8 Mm (Savcheva 2007). Histogram of velocity distribution has peak at approx. 140 km/s. Cirtain et al (2007) show outflows of 800 km/s. Jets formed on the south pole 60% likely to more eastward. SXR sources can shoot out multiple jets or just one before fading. These events seem similar to jets seen in active regions where the SXR source can be associated with a flare...maybe? Great multifilter observation of jet suggests cooling time is blackbody. Outflow component is millions of kelvin.

frequency of jet formation 7 per hour per coronal hole derived from 1418 and 120 hours of observation.

Jets in ARs and quiet Sun may be different since quiet sun jets do not have to contend with closed magnetic fields.

The Quiet Sun that wasn't by P. Grigis

Hinode allocations, SOT (70%), EIS (15%), XRT (15%). Averaging multiple frames (hours worth) yields much higher signal to noise. Gradient of that image shows many interesting structures. Geyser are defined as jets that go off multiple times. XRT observes small scale brightenings which are being called nanoflares for now. A peak finding algorithm can find active pixels. Bright points are found to be more active than dimmer regions. Occur more in network boundaries. Using a filter ratio method than one particular event gives an temperature of 1.5 MK. Luminosity distribution shows a power law with an index of -2.24 but multipixel events are counted multiple times which would make it too steep.

Observations of the Thermal and Dynamic Evolution of a solar microflare by J. Brosius

New CDS staring mode with rapid cadence applied to compact GOES B2 flare also observed by EIT MDI, TRACE (1600 angstrom), RHESSI. Sources from EIT and RHESSI are offset by 7 arcseconds both near a small emerging magnetic island. TRACE image show complex structure...loops? ribbons? Relative doppler velocities observed at -15 to -20 km/s. Peaks in Fe XIX, Si XII, O V lines coicident in time with flare. Upflows are consistent with chromospheric evaporation (gentle evaporation not explosive). RHESSI observations show little or no nonthermal spectrum but with temperature of approx. 11 MK (pretty usual for a microflare). Analysis on another event is ongoing. For an M class flare, doppler velocities are -100 km/s but now explosive evaporation along with a gentle evaporation later on in the flare.

Hot Plasma in non-flaring active regions by Paola Testa

Testing nanoflare heating models (Real et al. 2008). Hot plasma in nonflaring ARs is thought to be heated by nanoflares. Predictions suggest hot plasma should exist (Klimchuk 2008). Using Hinode/EIS it is possible to check this. Unfortunately, temperature diagnostics with filters can be difficult and calibration is ongoing (for Be_med and Al_med). Filter rations give very hot temperatures 10^(7.5) K. Blending of lines is also an issue. Deblending of lines is necessary. A procedure is described by Young et al. 2006. These methods are being tested. If the temperatures are really that high then RHESSI should be able to see it so can use RHESSI to set a maximum temperature possible.

Wed (10-Dec-2008)

Meeting with Active Region Loops Group I

Active Region Loops Observational Constraints from Hinode by Helen Mason

Some open questions questions.

Hinode/EIS can solve many of these problems though rastering is slow. Del Zanna (2007) shows flows at different temperatures (warning! several EIS spectral lines are blended, seek help from someone on the EIS team to deal with this). Flows persist over several days. Tripathi et al. 2008 looks at multiple loops at many different lines. Velocity flows are seen along the AR loops red-shifted at cool temperatures (Si VII). Blue-shifted flows are seen in other parts of the AR at higher temperatures (FeX FeXII FeXIV FeXIII FeXV). Intensity variation across loop structures at decrease as temperature increases. This is thought to be a real effect and not instrumental. Maybe these loops were not heated up enough to have well defined hot temperature loops or maybe there is a high temperature background. Temperature along the loop rises from 0.8MK at the base to 1.5 MK at the loop top. They may be midly multithermal. Electrong density along loops show decreasing density as a function of height for SiX and FeXII (1010cm-3 falling to 108.5cm-3 at the top). Filling factors are found to be quite low 0.02 to 0.05 at 6.1 MK but close to 1 at 5.8 MK. Density map compared to magnetic field shows that magnetic field and density are correlated but only on the positive side of the polarity inversion line. Core of active region structure have higher densities and higher temperature (hot dense core) (>10^6.7 K and >10^10 cm^-3). Summary

Think about the model by Zwaan 1985.

EUV signatures of small scale heating in loop by S. Parenti

Ambiguity with word nanoflare

Here we talk about the second. Testing models to back out the statistical properties of the nanoflares (represented by a heating function) from EUV observations (Parenti et al. 2006). Results show that the filling factor must be small, the dominant cooling process is conduction. New results presented in Parenti & Young 2008. Nanoflare heating function has a power law with index of -1.7. Can find index for various elements. The power law index varies for each one. These results are consistent with others work.

RHESSI Microflares, Hinode, and Quiet Sun by I. Hannah

Add notes here

RHESSI Microflare Height Distribution by S. Christe

Average loop tilt is found ot be 44% but could be biased.

Thurs (11-Dec)

meeting with Flares

Thurs (11-Dec)

meeting with Flares

Hinode Flare Observations by J. Cirtain

XRT only has a few flare observations. Can choose how many pixels will be saturated. Flare Patrol mode. Each instrument can respond to a flare flag. If flare happened in FOV of SOT then it will recenter SOT to the flare. If outside of FOV then it does not go into flare mode. XRT can change the region of readout to the center of the flare. There is a possible delay between when XRT goes into flare mode if triggered by a flare and when the other instrument do the same. Shortest exposure time for XRT is 1 ms.

Hinode Flare observations and EIS by R. Milligan

EIS is better than CDS in all respects. Many different settings possible for EIS (very flexible). Slits (1 and 2 arcsec) and slots (40 and 260 arcsec). Currently 325 different studies with EIS (and therefore EIS planning programs) but only 5 of these are designed for flares. Flare ESIS observation show that footpoint line profiles have upflows and downflows. EIS currently running at 500 Mbits per day. Example observations possible 21 windows, 40x140 arcsec, 4 minutes cadence, no compression gives 2.5 hours of observation. It might be possible to significantly increase bandwidth by stealing from SOT which has 70% of data currently. In order to coordinate with RHESSI, practically it is necessary to create a plan that lasts a few hours in order to catch flares by chance.

end meeting with Flares

Microflare Heating From RHESSI Hinode Observations by R. Milligan

Chromospheric evaporation with Hinode/EIS. Investigate the high temperatures observed by RHESSI and HInode in microflares. B class flare. Ca II, Fe XII, Fe XV, ribbons with SOT ,He II emission aligns with CaII ribbons. One footpoint is red-shifted and the other is blue-shifted (both 14 km/s). This is a pre-annealing flare with RHESSI so spectra is a bit dodgy. Find a temperature of 15 MK, no evidence for nonthermal emission. Klimchuck (2008) can model DEM curve. Conclusion is higher temperature when less energy is used to accelerate electrons. Flows suggest a syphon flow from one footpoint to the other. The direction of the flow is contradicted by XRT brightening.

How well correlated are flows observed by SOT with HRT images? Are flows really related to HXR emission? Can we really interpret flows with footpoint evaporation?


Magnetic Field activities at the photosphere by Shimizu-san

Numerous small scale explosive energy releases are observed including active-region transient brightenings. Hinode/XRT sees lots of small activity/brightenings. Morphology is full of variety; pointlike, single or multiple loops. Observed by Yohkoh/HXT as well. Magnetic reconnection is thought to be the base mechanism. SOT should be able to give us a better idea of the magnetic morphology. Configurations considered are emerging flux, coalescence of current loops. Kano et al. 2008 compared XRT images and SOT and found related flux emergence which supports the reconnection by flux emergence. Moving magnetic features which may be a major driver for X-ray bright points (see Kano et al. 2008). Multiple or single loop brightenings drivers are unknown. Magnetic field properties of footpoints in umbra. Electric current is enhanced at and deside the area surrounded by flare ribbons. Observed current enhancements mean that twisted magnetic fields are formed. Observed current density is 35 mA/m^2. Almost one turn along the loop. Most of footpoints are not in magnetic flux regions. Low filling factor of 0.25. Magnetic flux of footpoints in plage is in order to 10^17-18 Mx.

Generation of nonthermal electrons in the quiet corona by Q. Chen

Ralchenko et al. (2007) find that 5% suprathermal electrons in 3-4 MK can account for unexpected brightnes in hot lines. Model coronal loop has coulomb collisions, radiation cooling, conduction losses. The energy input is turbulence. Using Fokker-Planck kinetic model. Radiation comes from Chianti. Hard flat spectra are created. Conclusions, only a very weak nonthermal tail is generated in steady state. Observed brighteness excesses may be from distinct temperatures being superposed in field of view.

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