The hemispheric power input (HPI) is a measure of power, measured in gigawatts (GW) in Earth’s upper atmosphere to indicate available power in the auroral zones around the north and south poles. The National Oceanic and Atmospheric Administration (NOAA) operates a series of satellites known as polar-orbiting environmental satellites (POES). NOAA’s POES satellites circle the globe and, as they do, collect information on the amount of energy particles in the solar wind colliding with Earth’s magnetosphere transfer into the upper atmosphere of Earth. This information is analyzed and used to produce the HPI. Based on all of the collected information being analyzed, a forecast for HPI is produced and the app uses this information to display the anticipated HPI over the next hour.
Normal, quiet HPI values hover around 10 GW under normal circumstances. When solar activity increases, this value can climb rather rapidly. It appears that the value of HPI can be measured up to 250 GW, but it is uncertain how high this could theoretically go. For the purposes of the app, values of 10-13 GW appear to be good for 64 degrees latitude and greater. Values of 15 GW to 25 GW appear to be good for aurora activity near 60-62 degrees latitude. As the HPI continues to climb, the auroral oval continues to expand, and thus lower latitudes will begin to see aurora activity. This translates well into the OVATION model’s depiction of the auroral oval.
Free Versus Subscription
The free version of the app gives you approximately two hours and 30 minutes of HPI data: the previous 90 minutes plus the next hour. The subscription version lets you go back and look at HPI data for the past 36 hours in 6-hour increments. It also allows you to set up alerts based on the HPI value you wish to be alerted for.