Letter to the Editor

Energy spectrum of interplanetary magnetic flux ropes and its connection with solar activity

¹ Purple Mountain Observatory, 2 West Beijing Road, Nanjing 210008, PR China e-mail: djwu@pmo.ac.cn
² Department of Physics, Luoyang Normal College, Luoyang, PR China
³ Institute of Space Science, National Central University, Chungli 32001, Taiwan

Received: 30 November 2007
Accepted: 17 January 2008

Abstract

Context.Recent observations of the solar wind show that interplanetary magnetic flux ropes (IMFRs) have a continuous scale-distribution from small-scale flux ropes to large-scale magnetic clouds.

Aims.In this work, we investigate the energy spectrum of IMFRs and its possible connection with solar activity.

Methods.In consideration of the detectable probability of an IMFR to be proportional to its diameter, the actual energy spectrum of IMFRs can be obtained from the observed spectrum based on spacecraft observations in the solar wind.

Results.It is found that IMFRs have a negative power-law spectrum with an index α = 1.36±0.03, which is similar to that of solar flares, and is probably representative of interplanetary energy spectrum of coronal mass ejections (CMEs), that is, the energy spectrum of interplanetary CMEs (ICMEs). This indicates that the energy distribution of CMEs has a similar negative power-law spectrum. In particular, there are numerous small-scale CMEs in the solar corona, and their interplanetary consequences may be directly detected in situ by spacecraft in the solar wind as small-scale IMFRs, although they are too weak to appear clearly in current coronagraph observations.

Conclusions.The presence of small-scale CMEs, especially the energy spectrum of CMEs is potentially important for understanding both the solar magneto-atmosphere and CMEs.