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We analyze the residual errors for the Wang‐Sheeley‐Arge (WSA) solar wind speed forecasts as a function of the photospheric magnetic field expansion factor (fp) and the minimum separation angle (d) in the photosphere between the footpoints of open field lines and the nearest coronal hole boundary. We find the map of residual speed errors are systematic when examined as a function of fp and d. We use these residual error maps to apply corrections to the model speeds. We test this correction approach using 3‐day lead time speed forecasts for an entire year of observations and model results. Our methods can readily be applied to develop corrections for the remaining WSA forecast lead times which range from 1 to 7 days in 1‐day increments. Since the solar wind density, temperature, and the interplanetary magnetic field strength all correlate well with the solar wind speed, the improved accuracy of solar wind speed forecasts enables the production of multiday forecasts of the solar wind density, temperature, pressure, and interplanetary field strength, and geophysical indices. These additional parameters would expand the usefulness of Air Force Data Assimilative Photospheric Flux Transport‐WSA forecasts for space weather clients. Plain Language Summary: We significantly improve the accuracy of the Wang‐Sheeley‐Arge solar wind speed forecasts by correcting the speeds using the residual speed errors as a function of two quantities. Those two quantities are how close the magnetic field line footpoints are to the coronal hole boundary, and how much the magnetic field lines in the corona bend. Our improved solar wind speed forecasts have the potential to enable multiday forecasts of the solar wind density, temperature, and interplanetary magnetic field strength since these quantities correlate well with the solar wind speed. Forecasts of these additional quantities are needed to improve multiday space weather forecasts. Key Points: Residual Wang‐Sheeley‐Arge solar wind speed errors are systematic versus both expansion factor and angle to the coronal hole boundaryWe improve solar wind speed forecast by correcting the model speeds using these systematic residual speed errorsImproved solar wind speed forecast accuracy can enable multiday solar wind density, temperature, and field strength forecasts [ABSTRACT FROM AUTHOR]

Abstract We analyze the residual errors for the Wang‐Sheeley‐Arge (WSA) solar wind speed forecasts as a function of the photospheric magnetic field expansion factor (fp) and the minimum separation angle (d) in the photosphere between the footpoints of open field lines and the nearest coronal hole boundary. We find the map of residual speed errors are systematic when examined as a function of fp and d. We use these residual error maps to apply corrections to the model speeds. We test this correction approach using 3‐day lead time speed forecasts for an entire year of observations and model results. Our methods can readily be applied to develop corrections for the remaining WSA forecast lead times which range from 1 to 7 days in 1‐day increments. Since the solar wind density, temperature, and the interplanetary magnetic field strength all correlate well with the solar wind speed, the improved accuracy of solar wind speed forecasts enables the production of multiday forecasts of the solar wind density, temperature, pressure, and interplanetary field strength, and geophysical indices. These additional parameters would expand the usefulness of Air Force Data Assimilative Photospheric Flux Transport‐WSA forecasts for space weather clients.

The subsolar magnetosheath is penetrated by transient enhancements in dynamic pressure. These enhancements, also called high-speed jets, can propagate to the magnetopause, causing large-amplitude yet localized boundary indentations on impact. Possible downstream consequences of these impacts are, e.g., local magnetopause reconnection, impulsive penetration of magnetosheath plasma into the magnetosphere, inner magnetospheric and boundary surface waves, drop outs and other variations in radiation belt electron populations, ionospheric flow enhancements, and magnetic field variations observed on the ground. Consequently, jets can be geoeffective. The extend of their geoeffectiveness is influenced by the amount of mass, momentum, and energy they transport, i.e., by how large they are. Their overall importance in the framework of solar wind-magnetosphere coupling is determined by how often jets of geoeffective size hit the dayside magnetopause. In this paper, we calculate such jet impact rates for the first time. From a large data set of Time History of Events and Macroscale Interactions during Substorms (THEMIS) multispacecraft jet observations, we find distributions of scale sizes perpendicular and parallel to the direction of jet propagation. They are well modeled by an exponential function with characteristic scales of 1.34RE (perpendicular) and 0.71RE (parallel direction), respectively. Using the distribution of perpendicular scale sizes, we derive an impact rate of jets with cross-sectional diameters larger than 2RE on a reference area of about 100RE2 of the subsolar magnetopause. That rate is about 3 per hour in general, and about 9 per hour under low interplanetary magnetic field cone angle conditions (