The effect of smoothed solar wind inputs on globalmodeling results

摘要

1 This study investigates the role of fluctuations in the solar wind parameters intriggering a magnetic storm and assesses the storm simulation ability of the Space WeatherModeling Framework (SWMF) through a model–data comparison. The event of22 September 1999 is examined through global magnetosphere simulations, using as inputAdvanced Composition Explorer (ACE) observations (4 min temporal resolution) alongwith running averages of this data with windows of 60, 120, and 180 min. It is noted thatfor this storm the model produces a two phase, fast then slow recovery phase due to asudden drop in plasma sheet density during the interval of southward interplanetarymagnetic field (IMF). Also, smoothing the input with a window larger than 60 minchanges the entire magnetosphere and reduces the plasma sheet density and pressure,therefore a less intense storm develops. It is worth mentioning that the main phase(measured from Storm Sudden Commencement to minimum Dst) for this magnetic stormlasted about 3 h. This explains the change in the Dst profile for the 120 and 180 minaveraged input. Averaging only IMF B, or solar wind density reveals that all inputparameters are important for the development of the storm, but B, is the most significant.Also, comparison with Dst predictions (using the formula of O'Brien and McPherron(2000)) are presented and discussed. For all cases studied, there are no significantdifferences for Cross Polar Cap Potential (CPCP) in both hemispheres, while the nightsideplasma sheet density shows a sharp drop when the input is averaged over 60 min or more.Our results indicate that the magnetosphere responds nonlinearly to the changes in theenergy input, suggesting the need for a threshold in the amount of energy transferred to thesystem in order for the ring current to develop. Further increase of the energy input leads toa saturation limit where the inner magnetosphere response is no longer affected by anyadditional amount of energy contained within high-frequency oscillations, because themagnetospheric system acts as a low-pass filter on the interplanetary magnetic field.