1 / 25

Variation of Geomagnetic Responses to the Solar Wind Input: Long-Term Change and Half-Year Increase

This study investigates the long-term change and half-year increase in geomagnetic responses to solar wind inputs. It also explores the variation in the auroral location and the implications for space weather forecast.

benniee
Download Presentation

Variation of Geomagnetic Responses to the Solar Wind Input: Long-Term Change and Half-Year Increase

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Long-term change, Half-year increase during declining phases, and 2009 specialty at fixed latitudes Variation of geomagnetic responses to the solar wind input: M. Yamauchi and B. Olsthoorn IRF, Kiruna, Sweden Acknowledgement: Dst, Kp, AL, SYM/ASY, PC and sunspot numbers (RI) are provided by World Data Center for Geomagnetism, Kyoto University, Japan, GFZ, Adolf-Schmidt-Observatory Niemegk, Germany, and the Royal Observatory of Belgium, Brussels. Including these indices, all data are obtained from NASA-GSFC/SPDF through OMNIWeb (http://omniweb.gsfc.nasa.gov/ow.html).

  2. Long term (50 years) change in AE response to solar wind condition (hourly value), which cannot be explained by difference in recent history of activity (solar cycle phase). • Study of 2009 singularity suggested latitudinal-shift of ionospheric current. • Aurora location during growth phase seems to moved north after 2006. • Magnetic North Pole is quickly actually moving north, that might shift the “substantial” AE latitude Motivation

  3. (1) for Long Trend • Possibility 1: Due to shift of the auroral oval location • High-risk latitude for hazardous ground currents may change • Possibility 2: Actual change in the energy coupling efficiency • Prediction must be renewed every solar cycle • (2) for Solar Cycle Phase Difference • These possible causes (1 & 2) could also be also phase-dependent • Risk of hazard can also be phase-dependent Implication to Space Weather Forecast

  4. Consequence of shift of auroral latitude

  5. AE cannot be used for Sun-Earth coupling efficiency ? Shift of auroral latitude

  6. AE cannot be used for Sun-Earth coupling efficiency ? AE can be used to monitor the auroral location by combining with ASY_D and PC ⇒ High-risk latitude for hazardous ground current may change Shift of auroral latitude

  7. Using 5-min NASA/OMNI solar wind data, we calculate ' = (4π/µ0)·VBtan2sin4(C/2), and dΦ/dt = (V2SW·Btan·sin4(θc/2))2/3 • Obtain average AE, PC, and SYM/ASY for given ’and dΦ/dt • Travel time the spacecraft to the Earth is considered. • Different “integrated inputs” (5-60 min before) are compared ⇒ the correlation is best for 60 min average. • Average the result every 3-month to separate "equinox” and solstice. • Compare with 3-months variation of ’ and dΦ/dt to remove anomaly due to “pre-condition” difference. Method

  8. Why not examine meridian chain (IMAGE, Greenland etc)? • ⇒ 1. Future work. • 2. We want to show that indices are useful for this purpose. • Why not to use ”wide latitudinal-range” indices such as ap? • ⇒ 1. Purpose is different. • 2. We want to show that AE is useful for this purpose. Why not

  9. Result / overview of“AL response” • Enhancement of ~ 0.5-year during declining phase? • Long-term decreasing trend with 2009 minimum?

  10. Due to “pre-condition” difference ? Cause of latitudinal shift of Aurora

  11. The singular period does not match with the declining phase peak of solar wind input

  12. Due to “pre-condition” difference ? • Not related to “pre-condition” (most likely) Cause of latitudinal shift of Aurora

  13. @ higher latitude (similar)

  14. @ lower latitude (different)

  15. (1) Phase difference • divide into 4 phases • take relative values against average • Result: 50% more • weak-moderate conditions • not storm time Valid range of ’and dΦ/dt ? ’ dΦ/dt

  16. @ higher/lower latitudes Result: PC/AU are similar SYM-H is unclear, ASY-D not at all

  17. ’ dΦ/dt (2) Long-term (cycle-to-cycle) trend • divide into different cylcles (#21 and #24 are not complete, though) • take relative values against average • Result: decreasing trend over 4 cycles

  18. @ higher/lower latitudes Result: AU/SYM-H are similar PC similar only clycle #24, ASY-D not at all

  19. Interpreting by latitudinal shift of quiet-time aurora singular period = returning to AE stations

  20. (1) For quiet to moderate solar wind input (|AL| < 400 nT activity on average), the AL, AU, and PC responses to the same solar wind input increased for about 3-12 months during 1983, 1994, 2003, and 2016, immediately-after the early declining-phase massive CME period. Some increase for SYM-H, but not for ASY-D (enhance rather post-maximum). ⇒ Consistent with equatorward shift of the quiet-time polar cap and most likely not related to the pre-condition difference. (2) AL and AU responses to the same solar wind input continuously decreased over 30 years (at least until 2009). Summary • Future work: • Same analyses using meridian chain (IMAGE, Greenland) midnight data? • Identify auroral location using all-sky camera network

  21. End / extra slides

  22. Result / overview (why we take equinox) same result for dΦ/dt as ' solstice: more AE/SYM stations in the northern hemisphere

  23. Same for hourly value (since 1965) Result: smaller during 2005-2014 (x~ cycle #24) than before (Yamauchi, 2015)

  24. singular year = returning to (d) from (e) Consequence of shift of Quiet-time auroral latitude

More Related