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Solar Radiation Departures

07 Aug 2025 05:30 AM
A few recent requests to the IEM have wondered about solar radiation departures. These values are difficult to come by due to lack of observations, lack of robust climatologies, and general familiarity / applicability with what the values even mean. One approach is to use a model with near real-time estimates and a long term archive to attempt such a departure calculation. The IEM merges a couple of model estimates of solar radiation with the standard COOP daily observations to provide a downloadable dataset. The featured image looks into the NASA POWER estimates for Ames with 2025 daily values compared with period of record estimates back to 1984. A daily departure is plotted on the top panel and an accumulated departure is plotted within the bottom panel. This estimates a net positive ~50 Megajoules (MJ) departure since 1 May. One way to contextualize that value is that a sunny day this time of year should yield at least 25 MJ, so that departure would indicate a bonus of two extra sunny days vs an average accumulation. One item to note is that there are data availability lags with datasets like NASA POWER, so the plot indicates data only available up till 2 August.

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Doubling of Radiation

26 Feb 2025 05:30 AM
The continued lengthening of daylight time and warmer temperatures certainly have many Iowans thinking about spring. We are already two months removed from the shortest daylight day of the year and the associated change in radiation is the subject of today's daily feature. The chart presents a daily solar radiation climatology for Ames based on ERA5-Land along with 2025 obs based on the same and supplemented by near real-time NCEP HRRR model data. The side panels are diagnostics between the various available sources that the IEM merges with daily COOP data for download. Note that some of these sources have yet to have 2025 data, so thus why they are blank. Anyway, the point of the chart is to show that recent daily solar radiation values around 15 megajoules are roughly double of what climatology shows to start off January. This increase in energy certainly helps to bring spring time to the state.

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Tags:   solarrad