dorsal/arxiv
View SchemaScaling and a Fokker-Planck model for fluctuations in geomagnetic indices and comparison with solar wind epsilon as seen by WIND and ACE
| Authors | B. Hnat, S. C. Chapman, G. Rowlands |
|---|---|
| Categories | |
| ArXiv ID | physics/0412063 |
| URL | https://arxiv.org/abs/physics/0412063 |
| DOI | 10.1029/2004JA010824 |
Abstract
The evolution of magnetospheric indices on temporal scales shorter than that of substorms is characterized by bursty, intermittent events that may arise from turbulence intrinsic to the magnetosphere or may reflect solar wind-magnetosphere coupling. This leads to a generic problem of distinguishing between the features of the system and those of the driver. We quantify scaling properties of short term (up to few hours) fluctuations in the geomagnetic indices AL and AU during solar minimum and maximum along with the parameter epsilon that is a measure of the solar wind driver. We find that self-similar statistics provide a good approximation for the observed scaling properties of fluctuations in the geomagnetic indices, regardless of the solar activity level, and in the epsilon parameter at solar maximum. This self-similarity persists for fluctuations on time scales at least up to about 1-2 hours. The scaling exponent of AU index fluctuations show dependence on the solar cycle and the trend follows that found in the scaling of fluctuations in epsilon. The values of their corresponding scaling exponents, however, are always distinct. Fluctuations in the AL index are insensitive to the solar cycle as well as being distinct from those in the epsilon parameter. This approximate self-similar scaling leads to a Fokker-Planck model which, we show, captures the probability density function of fluctuations and provides a stochastic dynamical equation (Langevin equation) for time series of the geomagnetic indices.
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"abstract": "The evolution of magnetospheric indices on temporal scales shorter than that\nof substorms is characterized by bursty, intermittent events that may arise\nfrom turbulence intrinsic to the magnetosphere or may reflect solar\nwind-magnetosphere coupling. This leads to a generic problem of distinguishing\nbetween the features of the system and those of the driver. We quantify scaling\nproperties of short term (up to few hours) fluctuations in the geomagnetic\nindices AL and AU during solar minimum and maximum along with the parameter\nepsilon that is a measure of the solar wind driver. We find that self-similar\nstatistics provide a good approximation for the observed scaling properties of\nfluctuations in the geomagnetic indices, regardless of the solar activity\nlevel, and in the epsilon parameter at solar maximum. This self-similarity\npersists for fluctuations on time scales at least up to about 1-2 hours. The\nscaling exponent of AU index fluctuations show dependence on the solar cycle\nand the trend follows that found in the scaling of fluctuations in epsilon. The\nvalues of their corresponding scaling exponents, however, are always distinct.\nFluctuations in the AL index are insensitive to the solar cycle as well as\nbeing distinct from those in the epsilon parameter. This approximate\nself-similar scaling leads to a Fokker-Planck model which, we show, captures\nthe probability density function of fluctuations and provides a stochastic\ndynamical equation (Langevin equation) for time series of the geomagnetic\nindices.",
"arxiv_id": "physics/0412063",
"authors": [
"B. Hnat",
"S. C. Chapman",
"G. Rowlands"
],
"categories": [
"physics.space-ph",
"physics.geo-ph"
],
"doi": "10.1029/2004JA010824",
"title": "Scaling and a Fokker-Planck model for fluctuations in geomagnetic indices and comparison with solar wind epsilon as seen by WIND and ACE",
"url": "https://arxiv.org/abs/physics/0412063"
},
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