Recently, the research team of space science has published their new progress entitled “The Dependence of Cold and Hot Patches on Local Plasma Transport and Particle Precipitation in Northern Hemisphere Winter” online in Geophysical Research Letters (GRL) (Zhang Duan, et al., 2022, JCR Q1). Professor Zhang Qinghe, a core member of the team, is the corresponding author, and Zhang Duan, a doctoral student of the team, is the first author. Shandong University is the first and corresponding author institute.

The polar region is a natural window opening to space on the Earth, where the Earth’s magnetic field lines are extremely convergent and vertical in and out. Therefore, the polar ionosphere is one of the key regions in the processes of solar-terrestrial energy coupling, and the dynamic processes can also be directly mapped to the polar ionosphere resulting in various irregularities. One of the various irregularities is the polar cap patch, whose densities are at least twice that of the surrounding regions, ranging from hundreds to thousands of kilometres. As polar cap patches move, strong electron density gradients can occur along their edges, which may cause strong scintillations of trans-ionospheric signals including ground-to-satellite communications and other navigation applications. Understanding the key features, formation mechanism and evolution characteristics of polar cap patches is thus of key importance for space weather modelling and forecasting. It is also one of the hottest and most difficult topics in the international polar ionosphere-magnetosphere coupling research.

The polar cap patch is an important research direction of polar ionosphere-magnetosphere coupling group at the Institute of Space Sciences of Shandong University. The group has successively achieved a series of research results in the formation and evolution of polar cap patches and their associated upflows and scintillations (more than 15 SCI papers have been published, including 1 Science paper and 7 GRL papers, etc.). Recently, the research group has also classified polar cap patches: cold patches (high density and low electron temperature) and hot patches (high density and high electron temperature), and found that cold and hot patches have different space weather effects and different dependence on solar activities. For example, the occurrence of cold patches is clearly dependent on solar and geomagnetic activity, while hot patches do not show such dependence; in the northern hemisphere winter, the spatial size of both cold and hot patches decreases (increases) with solar (geomagnetic) activity, etc. (Zhang Duan, et al., 2021). However, the dependence of cold and hot patches on local plasma transport and soft-electron precipitation is so far unknown.

In this work, under the guidance of Prof. Zhang Qinghe, Zhang Duan et al. surveyed a database of 4,634 cold patches and 4,700 hot patches from the Defense Meteorological Satellite Program (DMSP) F16 for the years 2005-2018 winter months to identify the distributions of polar cap patches for different IMF orientations and ionospheric convection geometries. The results indicate that: In winter, (1) more cold and hot patches occur in the stronger anti-sunward flow organized by different IMF orientations (Figure 1). (2) cold patches are frequent near the central polar cap, while hot patches are closer to the auroral oval (Figure 2). (3) enhanced anti-sunward flow (E x B drift) mainly contributes to cold patch occurrence under Bz<0, and soft-electron precipitation contributes to hot patch occurrence both under southward and northward IMF (Figure 3).

This work was supported by the National Natural Science Foundation, the China Research Institute of Radiowave Propagation, the Chinese Meridian Project and the China Postdoctoral Science Foundation, etc.

Related papers:

Duan Zhang, Qing-He Zhang, Y.-Z. Ma, Kjellmar Oksavik, L. R. Lyons, Z.-Y. Xing, Marc Hairston, Z.-X. Deng, J.-J. Liu. (2022). The dependence of cold and hot patches on local plasma transport and particle precipitation in Northern Hemisphere winter. Geophysical Research Letters, 49, e2022GL098671. https://doi.org/10.1029/2022GL098671

Duan Zhang, Qing-He Zhang, Y.-Z. Ma, Kjellmar Oksavik, L. R. Lyons, Y.-L. Zhang, Balan Nanan, Z.-Y. Xing, Jing Liu, Marc Hairston, X.-Y. Wang. (2021). Solar and geomagnetic activity impact on occurrence and spatial size of cold and hot polar cap patches. Geophysical Research Letters, 48, e2021GL094526.https://doi.org/10.1029/2021GL094526.

Figure 1. The spatial MLAT-MLT distributions of the dayside cold (blue) and hot (red) patches superimposed on the statistical ionospheric convection patterns (electrostatic potentials in kV, gray lines) for eight45^o-wide clock angles centered about θ = (a) -45^o, (b)0^o, (c) 45^o,etc. The yellow lines highlight the statistical poleward boundary of the auroral oval. The numbers of cold and hot patches are marked in the upper right corner of each panel.

Figure 2. MLAT versus clock angle distributions of (a1-a4) patch occurrence, (b1-b4) O⁺density, (c1-c4) electron temperature (Te), (d1-d4) soft-electron (<1keV) energy flux, and (e1-e4) the cross-track velocity (V_cross-track). The two columns on the left correspond to cold patches, and the two columns on the right correspond to hot patches. The distributions are binned over 1^oMLAT and 10^oclock angle. The black/magenta lines in panels a1-a4 identify the MLAT with the highest patch occurrence versus clock angle (the magenta dashed lines in panels a1-a2 are overlaid from the magenta solid lines panels a3-a4 for easier comparison between hot and cold patches).

Figure 3. Occurrence of polar cap patches versus (a and c) anti-sunward velocity and (b and d) soft-electron energy flux. Panels a and b correspond to southward IMF (i.e. more negative velocity), and panels c and d correspond to northward IMF. The dotted blue and red lines show the relative occurrence rates of the cold and hot patches, respectively.