A New Index to Describe the Response of Geomagnetic Disturbance to the Energy Injection from the Solar Wind

In this paper, we establish a new non-dimensional global geomagnetic disturbance index <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msubsup><mi>J</mi><mi>p</mi><mi>G</mi></msubsup></semantics></math></inline-formula> by applying the spectral whitening method to the horizontal components of geomagnetic fields observed at eight ground-based stations distributed at low and middle latitudes during years 1998 to 2014. This index can describe the development of geomagnetic storms and its relationship with the Dst index has been verified, which gives a correlation coefficient (CC) of about 0.72. We also check the response of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msubsup><mi>J</mi><mi>p</mi><mi>G</mi></msubsup></semantics></math></inline-formula> to the arrival of upstream solar wind energy based on a proxy that the ring current injection term <i>Q</i>. The variation of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msubsup><mi>J</mi><mi>p</mi><mi>G</mi></msubsup></semantics></math></inline-formula> in course of geomagnetic storms is similar to the variation of <i>Q</i>, and the recorded minimum values of <i>Q</i> (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>Q</mi><mrow><mi>m</mi><mi>i</mi><mi>n</mi></mrow></msub></semantics></math></inline-formula>) and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msubsup><mi>J</mi><mi>p</mi><mi>G</mi></msubsup></semantics></math></inline-formula> (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow><msubsup><mi>J</mi><mi>p</mi><mi>G</mi></msubsup></mrow><mrow><mi>m</mi><mi>i</mi><mi>n</mi></mrow></msub></semantics></math></inline-formula>) for 30 great storms yields a relatively better CC of about 0.82. These results illustrate that <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msubsup><mi>J</mi><mi>p</mi><mi>G</mi></msubsup></semantics></math></inline-formula> can effectively depict the storm evolution and is well related to the associated <i>Q</i> in amplitude, which provides an alternative means of geomagnetic storm forecasting. In addition, we note that the time difference between <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>Q</mi><mrow><mi>m</mi><mi>i</mi><mi>n</mi></mrow></msub></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow><msubsup><mi>J</mi><mi>p</mi><mi>G</mi></msubsup></mrow><mrow><mi>m</mi><mi>i</mi><mi>n</mi></mrow></msub></semantics></math></inline-formula>, as well as the time difference when <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msubsup><mi>J</mi><mi>p</mi><mi>G</mi></msubsup></semantics></math></inline-formula> recovers from <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow><msubsup><mi>J</mi><mi>p</mi><mi>G</mi></msubsup></mrow><mrow><mi>m</mi><mi>i</mi><mi>n</mi></mrow></msub></semantics></math></inline-formula> to half and/or one-third of its value, are shorter than those of the corresponding Dst index. And especially, for multiple storms that occurred continuously on a short time scale, the recovery of the Dst index to a quiet period level can be affected by the following solar wind energy input, while the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msubsup><mi>J</mi><mi>p</mi><mi>G</mi></msubsup></semantics></math></inline-formula> index does not and exhibits independently.