Browsing by Author "Liemohn, Michael W."
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- Conductance Model for Extreme Events: Impact of Auroral Conductance on Space Weather ForecastsMukhopadhyay, Agnit; Welling, Daniel T.; Liemohn, Michael W.; Ridley, Aaron J.; Chakraborty, Shibaji; Anderson, Brian J. (2020-09-27)Ionospheric conductance is a crucial factor in regulating the closure of magnetospheric field-aligned currents through the ionosphere as Hall and Pedersen currents. Despite its importance in predictive investigations of the magnetosphere-ionosphere coupling, the estimation of ionospheric conductance in the auroral region is precarious in most global first-principles-based models. This impreciseness in estimating the auroral conductance impedes both our understanding and predictive capabilities of the magnetosphere-ionosphere system during extreme space weather events. In this article, we address this concern, with the development of an advanced Conductance Model for Extreme Events (CMEE) that estimates the auroral conductance from field-aligned current values. CMEE has been developed using nonlinear regression over a year's worth of 1-min resolution output from assimilative maps, specifically including times of extreme driving of the solar wind-magnetosphere-ionosphere system. The model also includes provisions to enhance the conductance in the aurora using additional adjustments to refine the auroral oval. CMEE has been incorporated within the Ridley Ionosphere Model (RIM) of the Space Weather Modeling Framework (SWMF) for usage in space weather simulations. This paper compares performance of CMEE against the existing conductance model in RIM, through a validation process for six space weather events. The performance analysis indicates overall improvement in the ionospheric feedback to ground-based space weather forecasts. Specifically, the model is able to improve the prediction of ionospheric currents, which impact the simulated dB/dt and Delta B, resulting in substantial improvements in dB/dt predictive skill.
- Relationship between sawtooth events and magnetic stormsCai, Xia; Zhang, J. C.; Clauer, C. Robert; Liemohn, Michael W. (American Geophysical Union, 2011-07-01)The relationship between sawtooth events and magnetospheric substorms has been discussed extensively. However, the relationship between sawtooth events and magnetic storms has not been systematically examined. Using the sawtooth event list and magnetic storm list from January 1998 to December 2007, we investigate whether sawtooth events are storm time phenomena and whether there is a dependence on the strength and phase of storms. We have found that most of sawtooth events occur during storm time. Nevertheless, there are still 6 sawtooth events (5.4% of total events) that occur during nonstorm intervals. Sawtooth events also tend to occur during intense storms, with an occurrence rate of 63.5%. Sawtooth events can initiate during any stage of storms, however 55.9% of sawtooth events occur during the storm main phase through the time the ring current reaches its maximum strength. Therefore we conclude that sawtooth events are very often but not necessarily storm time phenomena. And not all storms contain sawtooth events. We suggest most sawtooth events occur during a special subset of storms that have just the right driving conditions to set intense, periodic, near-tail magnetic reconnection bursts.