Solar wind power is a value that is calculated based on measurements of physical properties of the solar wind (and CMEs when they occur). \u00a0The solar wind power increases in value as the speed of the solar wind and strength of its magnetic field increases. \u00a0The extent to which the magnetic field lines point in the Bz direction (see part 3) is also quantified in the calculations by describing the interplanetary magnetic field (IMF) clock angle. \u00a0The solar wind power increases as the IMF clock angle approaches the \u201c6 o\u2019clock position\u201d (that is, when Bz is approaching south).<\/p>\n
Solar wind power is measured in watts. \u00a0These watts are the same watts that are used to rate lightbulbs: the higher the wattage, the brighter the light bulb (when comparing two bulbs with the same efficiency). \u00a0Similarly for the aurora, the higher the wattage of the solar wind power, the brighter and larger the aurora will be. \u00a0However, the solar wind power is only proportional to aurora activity, not equivalent the way wattage is for light bulbs. \u00a0Aurorasaurus graphs the strength of the solar wind power here<\/a>. \u00a0based off of real-time measurements taken by ACE. \u00a0Since ACE is located at L1, it takes about an hour for the solar wind it measures to actually impact Earth. In this way, solar wind power is useful for anticipating aurora activity by looking at the average value over the last hour. Fluctuations minute-to-minute or huge spikes in the power will not greatly affect what latitudes the aurora will be seen.<\/p>\n Recall the windmill analogy from Part 2, where the aurora generated by the solar wind is like a windmill that is spun by regular wind. \u00a0A few strong gusts might get the blades to move a little bit, but if there is a strong sustained wind, then the blades can start and continue to spin. \u00a0Similarly, a few small spikes in the solar wind power may not be enough to stir up sustained aurora activity. \u00a0However, a sustained strong solar wind will be enough to stir up continuous aurora. \u00a0The solar wind power parameter was developed by eminent space physicist Dr. Akasofu<\/a> (who is also credited with coining the phrase \u201csub storm\u201d). \u00a0You can find more information about how solar wind power affects the aurora in Dr. Akasofu\u2019s 1981 paper<\/a>. As indicated by the yellow, orange and red labels on the solar wind power plot, the stronger the wind, the further south the aurora will be visible. \u00a0Note that the the color coded indicators approximate the furthest extent and intensity of the aurora.<\/p>\n![\"solar-wind-blog-post\"](\"https:\/\/blog.aurorasaurus.org\/wp-content\/uploads\/2015\/09\/solar-wind-blog-post.jpg\")
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