Zongjun Ning

9th RHESSI Workshop

Genova, Italy, September 1-5 2009

Participants

Zongjun Ning

Purple Mountain Observatory, Nanjing, China

Email: ningzongjun (at) pmo.ac.cn

Group 4

Contribution: We present the radio and hard X-ray evidences of chromospheric evaporation during an M1.0 flare which occurred on December 1, 2004. The radio emission was observed by the Solar Broadband Radio Dynamic Spectrometer in China, which yielded dynamic spectra of decimetric emission. The hard X-ray emission was observed by RHESSI. In the radio spectra, the burst is characterized by two groups of the parallel-drifting structures, some of which change their drifting rates from positive to negative. Based on the standard flare model, we may explain these decimetric bursts in terms of chromospheric evaporation. On the other hand, RHESSI observations show that the hard X-ray emission in the energy range of 10-15 keV tend to rise from two footpoints to the looptop and eventually merge into a single looptop source, which is accepted as the evidence of hard X-ray evidence of chromospheric evaporation. Such processes happened two time in this event. The drifting radio structures occurred between them, at the same time as the third hard X-ray peak at 25-50 keV.

Group 2

Contribution: The Neupert effect suggests a flare model in which the hard X-rays are electron-ion bremsstrahlung produced by energetic electrons as they lose their energies in the chromosphere and the soft X-rays are thermal bremsstrahlung from the “chromospheric evaporation” plasma heated by those same electrons. Based on this concept, we investigate the evidence of the chromospheric evaporation in a Neupert-type flare on 2004 October 30. First, we have to prove that this event does follow the Neupert effect. Using the RHESSI data, the thermal and nonthermal energies are derived after onset of this flare. The high correlation, with a coefficient of 0.60 between the derivative of thermal energy and the nonthermal energy indicates that the 2004 October 30 flare is a Neupert-type event. Second, the chromospheric evaporation is necessarily expected on its rising phase. We analyze the RHESSI images at the different energies and different times. The hard X-ray emission tends to move close the footpoints and finally merge into a single source with the same position as the looptop source. This is thought to be the signature of the chromospheric evaporation in the X-ray observations. After constructing a semi-circular flaring loop, we roughly measure the evaporation speeds of $\\sim$632 km s$^{-1}$ for the south footpoint, and $\\sim$397 km s$^{-1}$ for the north one. The evaporation speeds are measured as a function of the time.

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