The reporter learned from the Yunnan Observatory of the Chinese Academy of Sciences on the 14th that researchers recently found complete and clear observational evidence of the formation of solar dark stripes caused by chromosphere evaporation and coronal condensation. The relevant research results were published in the International Astronomical Journal astrophysics journal communication.

Solar filaments are common in the solar atmosphere. They are composed of cold and dense plasma suspended in the solar corona. The study on the formation and evolution of dark bars can provide a lot of valuable information for understanding solar atmospheric activities. Previously, the "chromosphere evaporation coronal condensation" research model proposed the principle of forming cold and dense dark stripe matter, but chromosphere evaporation has not been detected in the process of dark stripe formation. The origin of local heating at the foot of the dark bar chromosphere has not been clear, and this model also needs to be verified by observation.

Yang Bo, associate researcher of Fuxian Lake solar observation and research group of Yunnan Observatory, and his collaborators used the multi band imaging observation of solar dynamics observation satellite and its atmospheric imager combined with spectral observation to analyze the complete process of the formation of dark bars in an active area in 11967 active area on February 2, 2014. The observation of the solar dynamics observation satellite shows that the shear motion drives a series of runaway reconnection processes in the process of magnetic field emergence. These reconnections produce a bound flare accompanied by the formation of an S-shaped structure. They found that this structure was rooted in the brightening of a pair of conjugate foot points that bound the flare. In the pulse phase of the flare, the spectrometer detected that the explosive evaporation occurred at the brightening of the pair of conjugate feet. After the flare, coronal condensation occurs in this structure and finally forms a dark strip.

The research team speculated that the flare led to explosive evaporation at the foot of the S-shaped structure, which made the structure dense, resulting in increased radiation loss, thermal instability or thermal imbalance, and finally the hot plasma condensed to form a cold and dense dark strip.

This important discovery is the first direct detection of explosive chromosphere evaporation before the thermal imbalance. This observation can explain the hypothesis of local foot heating in the "chromospheric evaporation coronal condensation" model. In this model, foot point heating is essential, but its origin has been unclear. This observation confirms that the flare may be a source of foot point heating in the study model.