Today's chart is a bit of a deep dive into drivers for changes in soil temperature. A big current weather story is the cold soil temperatures statewide which are preventing crop planting progress. The featured chart attempts to look into what it takes to produce warmer soil temperatures, in particular four inch depth soil temperatures based on period of record data from the Ames ISU AgClimate weather station during the month of April. In focus is what may drive the day to day warming or cooling of soil temperatures. The top two panels present the relationship between the day to day change in air temperature and solar radiation with the response in day to day soil temperature. The bottom two panels look more into the absolute relationship between these three parameters. One may suggest that simply having sunny days are sufficient to increase soil temperatures. While the bottom left panel does show a positive relationship (increasing radiation increases the day to day temperature change), the correlation is a bit low and would indicate other factors are at play. The upper left plot shows a stronger relationship between day to day changes in air and soil temperatures, but this relationship is physically complex via the surface energy budget. Energy will flow from warmer soils to the air and from warmer air to the soil. During the spring time, a major source of warm air is from wind transporting warmer air into the state and from daytime mixing of warmer air aloft down to the surface. The moral of the story is that these plots seem to indicate that air temperatures are more important of a driver of soil temperatures than solar input. One could think of it this way, we just had our coldest 1-15 April period on record for air temperatures not wholly due to a lack of sunshine, but from dominant cold air masses being transported into the state. Of course, it also does not help to have snow covering the ground which will be added to today, sigh!

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Tags:   soiltemp