AUTHOR=Fasel G. J. , Lee L. C. , Lake E. , Csonge D. , Yonano B. , Bradley O. , Briggs J. , Lee S. H. , Mann J. , Sigernes F. , Lorentzen D. 

TITLE=Correlation between the solar wind speed and the passage of poleward-moving auroral forms into the polar cap

JOURNAL=Frontiers in Astronomy and Space Sciences

VOLUME=10

YEAR=2024

URL=https://www.frontiersin.org/journals/astronomy-and-space-sciences/articles/10.3389/fspas.2023.1233060

DOI=10.3389/fspas.2023.1233060

ISSN=2296-987X

ABSTRACT=<p>In 1961, Dungey suggested that magnetic reconnection occurs due to the solar-terrestrial interaction. The interplanetary magnetic field (IMF) is thought to merge with Earth’s geomagnetic field (GMF). After the reconnection process the newly formed magnetic flux tube, consisting of both the IMF and GMF, moves anti-sunward. Poleward-moving auroral forms (PMAFs) are believed to be the ionospheric signatures of this process, which transfers magnetic flux from the dayside to the nightside. This paper looks at the connection between the solar wind speed and the motion of the PMAF as it moves from the auroral oval, anti-sunward, into the polar cap. PMAFs are identified using both the meridian scanning photometer (MSP) and colored all-sky camera (ASC). Once the PMAFs are identified, the PMAF-SLOPE, <inline-formula id="inf1"><mml:math id="m1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">v</mml:mi><mml:mi mathvariant="normal">α</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> (units of degrees per time) and the angle (α<sub>PMAF</sub>) the PMAF makes with the horizontal (Time axis), in the MSP plot are calculated. These values (<inline-formula id="inf2"><mml:math id="m2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">v</mml:mi><mml:mi mathvariant="normal">α</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> and α<sub>PMAF</sub>) are individually plotted against the <inline-formula id="inf3"><mml:math id="m3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">v</mml:mi><mml:mi mathvariant="normal">x</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula>-component of the solar wind speed and the flow speed (total solar wind speed). The plots generate linear a relationship between PMAF-SLOPEs, <inline-formula id="inf4"><mml:math id="m4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">v</mml:mi><mml:mi mathvariant="normal">α</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula>, [or PMAF angles (α<sub>PMAF</sub>)], and the <inline-formula id="inf5"><mml:math id="m5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">v</mml:mi><mml:mi mathvariant="normal">x</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula>-component of the solar wind speed (or the flow speed). A total of 57 PMAF events from 8 different days were associated with solar wind speeds (<inline-formula id="inf6"><mml:math id="m6" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">v</mml:mi><mml:mi mathvariant="normal">x</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula>-component) ranging from 344 to 679 km/s. The first linear plot, between the PMAF-SLOPE and solar wind speed (<inline-formula id="inf7"><mml:math id="m7" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">v</mml:mi><mml:mi mathvariant="normal">x</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula>-component), shows a high correlation: <inline-formula id="inf8"><mml:math id="m8" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">r</mml:mi><mml:msub><mml:mi mathvariant="normal">v</mml:mi><mml:mi mathvariant="normal">α</mml:mi></mml:msub></mml:msub><mml:mrow><mml:mo>=</mml:mo><mml:mn>0.944</mml:mn></mml:mrow></mml:mrow></mml:math></inline-formula>. A second linear plot, between α<sub>PMAF</sub> and the solar wind speed (<inline-formula id="inf9"><mml:math id="m9" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">v</mml:mi><mml:mi mathvariant="normal">x</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula>-component) shows a very high correlation: <inline-formula id="inf10"><mml:math id="m10" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">r</mml:mi><mml:mrow><mml:mi mathvariant="normal">α</mml:mi><mml:mrow><mml:mi mathvariant="normal">P</mml:mi><mml:mi mathvariant="normal">M</mml:mi><mml:mi mathvariant="normal">A</mml:mi><mml:mi mathvariant="normal">F</mml:mi></mml:mrow></mml:mrow></mml:msub><mml:mrow><mml:mo></mml:mo><mml:mo>=</mml:mo><mml:mspace width=".17em" /><mml:mn>0.973</mml:mn></mml:mrow></mml:mrow></mml:math></inline-formula>. The conclusions obtained from this statistical study are: 1) both the PMAF-SLOPE <inline-formula id="inf11"><mml:math id="m11" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">v</mml:mi><mml:mi mathvariant="normal">α</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> and α<sub>PMAF</sub> are highly correlated to the <inline-formula id="inf12"><mml:math id="m12" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">v</mml:mi><mml:mi mathvariant="normal">x</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula>-component of the solar wind, increasing when <inline-formula id="inf13"><mml:math id="m13" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">v</mml:mi><mml:mi mathvariant="normal">x</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> increases and <italic>vice versa</italic>, 2) PMAFs must be connected to both the IMF and GMF and are dragged anti-sunward, mostly by the <inline-formula id="inf14"><mml:math id="m14" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">v</mml:mi><mml:mi mathvariant="normal">x</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula>-component of the solar wind, and 3) PMAFs are indeed the ionospheric footprints of a newly formed magnetic flux tube, due to dayside magnetic reconnection, being transferred from the dayside to nightside.</p>