Using Principal Component Analysis to Characterize the Variability of VLF Wave Intensities Measured by a Low‐Altitude Spacecraft and Caused by Interplanetary Shocks

다국어 초록 (Multilingual Abstract)

Very low frequency wave intensity measurements provided by the French low‐altitude DEMETER spacecraft are studied using the principal component analysis (PCA). We focus on both the physical interpretation of the first two principal components and their application to real physical problems. Variations of the first principal component (PC1) coefficients due to the geomagnetic activity and seasonal/longitudinal changes are studied. It is shown that their distribution corresponds to the wave intensity dependences obtained in previous studies. Moreover, the variations of PC1 coefficients around interplanetary shock arrivals are analyzed. The study is performed for fast forward (FF), fast reverse, slow forward, and slow reverse shocks separately. It shows that the most significant effect on the wave intensity is displayed in the FF case. Furthermore, it turns out that the wave intensity variations depend on the wave intensity detected before the shock arrival. Finally, the shock strength and interplanetary magnetic field orientation are also important. The performed analysis shows that PCA can be successfully applied to characterize large data sets of spacecraft measurements by limited sets of numbers—principal component coefficients (typically first one or two are enough), which still maintain a sufficient amount of information.



The principal component analysis is used to describe very low‐frequency wave intensity measured by the low‐altitude spacecraft DEMETER

First principal components are shown to correspond to the overall wave intensity measured in individual frequency‐latitude spectrograms

First principal component coefficients around the times of fast forward interplanetary shock arrivals exhibit systematic variations


The principal component analysis is used to describe very low‐frequency wave intensity measured by the low‐altitude spacecraft DEMETER
First principal components are shown to correspond to the overall wave intensity measured in individual frequency‐latitude spectrograms
First principal component coefficients around the times of fast forward interplanetary shock arrivals exhibit systematic variations