Local high-temperature phenomena within magnetic clouds

In this study, three methods were used to analyze 17 large-scale local high-temperature regions with durations exceeding 2 h within magnetic clouds (MCs) observed by advanced composition explorer from 1998 to 2008. Results show that five of these large-scale regions may have been caused by flare heating; seven of the regions may have been caused by nonuniform expansion when MCs propagated in the solar-terrestrial space; four large-scale high temperature regions may likely result from combined non-uniform expansion and flare heating; and only one large-scale local high-temperature region was not related to either flare heating nor non-uniform expansion. No evidence indicated that magnetic reconnection occurred or had occurred within the high-temperature regions. Based on our results, we infer that such local high-temperature phenomena within MCs are caused primarily as a result of flare heating and non-uniform expansion, either separately or jointly, and that magnetic reconnection plays only a minor role in the formation of high-temperature regions.