Observation of the lower hybrid waves near the three-dimensional null pair

Magnetic reconnection is a fundamental process in plasma, which is thought to play important roles both in laboratory and natural plasmas through affecting magnetic topology, heating and accelerating particles. During an event on Oct. 1st, 2001, the Cluster tetrahedron circled around the magnetic reconnection region several times, and Xiao et al. first identified the null pair and found that the spectrum of the null-point oscillation shows the maximum power near the lower-hybrid frequency. In this paper we report the observation of electromagnetic and electrostatic wave enhancements near lower hybrid frequency associated with the reconnection process near the null pair. The lower hybrid waves (LHWs) with quasi-perpendicular propagation were identified and also confirmed by the power law of the spectrum of electric and magnetic fields. Supported by the National Natural Science Foundation of China (Grant Nos. 40325012, 40390151, 40574073, 40574074, and 40640420563), the Research Foundation from Ministry of Education of China (Grant No. 40174043), and the China Plan on the International Polar Year