北极中央区海冰低密集度现象研究

近年，北极中央密集冰区出现海冰低密集度的异常现象。为了探讨这一现象的成因，本文使用ERA-Interim再分析资料，定义了北极中央区海冰低密集度（LCCA）指数，研究了2009-2016年的6-9月北极中央区发生的海冰低密集度现象。分析表明，研究时段内在北极中央区发生了6次明显的海冰低密集度（LCCA峰值）过程。在这些过程中，局地气温异常并不是导致海冰低密集度现象发生最主要的因素；海冰低密集度区域的形态及冰速场分布均与大气环流场相对应；在LCCA指数峰值发生前均有气旋中心出现在北冰洋70°N以北并伴随向北移动，气旋引起海冰辐散，同时所携带的较低纬度的热量导致海冰迅速融化。在6次过程中，有3次为气旋影响配合北极偶极子（DA）型环流。LCCA指数与84°N平均向北温度平流和北极中央区海冰速度散度呈正相关。在LCCA指数峰值前，温度平流对海冰低密集度区域形成的影响大于海冰辐散的影响。

Exploration of anomalous low sea ice concentration phenomenon in the Central Arctic

In recent years, there emerges a phenomenon that Central Arctic should experience anomalous low sea ice concentration. To analyze explicitly the causes, the Low Concentration in Central Arctic (LCCA) index is defined by using the ERA-Interim reanalysis data. Within the period of June to September from 2009 to 2016, there were 6 cases recognized as the peaks of LCCA index. The results show that the leading factor of low sea ice concentration is not the local thermal condition. Dynamically, the drifting pattern of sea ice and the location of region with low sea ice concentration response consistently to the atmospheric circulation. Particularly, cyclones used to be found north of 70°N before the 6 peaks of LCCA index occurred. These cyclones moved towards north with hot air from lower latitudes causing divergence and rapid melting of sea ice. In 3 cases of 6, cyclones were accompanied with Dipole Anomaly (DA) pattern. LCCA index correlates positively with northward heat advection across the circle of 84°N as well as the divergence of Central Arctic sea ice. Before the LCCA peak days, the northward heat advection has greater effects on sea ice than the dynamic divergence.