Solar Cycle 24 Group G

From RHESSI Wiki

Introduction

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

Microflares so what

• small events are numerous, can be studied statistically as well as individually
• simpler coronal configuration?

why now?

• RHESSI and Hinode!
• relationship with chromospheric reconnection by Hinode/SOT
• events easier to observe during solar minimum.

who cares?

• small events do not suffer from large flare syndrome.
• nanoflare heating?
• scaling laws
• what are smaller events like?

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.