Weather Forecast



Frost before it freezes

This monthly column takes some crazy sounding ideas and applies them to the field of Ag Tech. The purpose of this is purely entertainment, but hey, if we can spread ideas or ignite imaginations, how awesome is that?

Heat is transferred in three ways. Conduction is heat that is transferred by direct touch. Convection is heat transferred by the movement of fluids or air.

Radiation is the third type of heat transferral which uses infrared light in its processes. Oddly enough, infrared goes through the atmosphere better at certain frequencies.

Infrared wavelengths between 8 and 13 micrometers gets through our atmosphere and into space the best. Researchers at Stanford have developed a material that both reflects and allows infrared energy to pass through the material in these wavelengths. This material is built to allow radiant heat off of buildings and at the same time reflect back radiant heat from other sources and the sun — reducing cooling costs significantly.

Just about everything radiates out infrared heat, including our soil and plants. This is why on a clear night, the risk for frost is greater than on a cloudy night. With no cloud cover on a clear night, your soil and plants radiate heat out into space. This invisible heat shoots straight to space and is lost in the vacuum until it hits another planet or object. Whereas during cloudy nights, that heat can get reflected back to the ground.

It is also because of the radiant heat lost during the transfer to space that your thermometer can read above freezing temperatures while there is frost on the ground. In addition, cooler, denser air falls to the ground (causing frost), while the thermometer reads the air temperature of the warmer, higher air.

Dispositional frost and frozen dew are the two types of "frost" that can occur. Dispositional frost is frost that formulates when reaching the dew point while the temperature is already below freezing.

Frozen dew is more unique in the way it forms. Frozen dew is made when long-range radiation cooling occurs and then lowers the temperature to, or below, freezing.

The grape industry (and possibly all orchards) lay rocks around their vines in order to protect their crops. The radiant sun heats up the rocks all day, so that the rocks release the radiant heat back into the atmosphere when night falls. This keeps grapevines warmer when the risk of frozen dew is at its greatest.

Frost can destroy crops and create a negative economic impact. Protecting your crop from the grips of frost is not an easy feat. I mean, theoretically, you could plug in a bunch of heaters across the miles of your field, but the energy to protect your crop this way is pretty insane. At that point, it'd be easier to just replant. In orchards, you can lay rocks down, but who's going to do that in row crops?

A little bit of science and a dash of new products could provide another option. Stanford engineers are (rightfully so) concerned with the largest market of cooling buildings down and reducing energy usage. While they're tied up, I propose a new way of preventing frost by utilizing the material those Stanford engineers came up with to reflect radiants. What a person could do is simply turn the material upside down, and redirect the long range radiant heat from the soil and plants right back to the ground. This would keep the radiant heat from making its journey to space, and put it back to work — keeping the crops warm. Temporary tents or balloons carrying the material could float up over areas at risk and prevent frost by deflecting the radiant heats back down. These tents or balloons could be used over and over again, so when you are finished, just like your equipment, you put it back in the shed.

The economic return is greater than just frost prevention on the occasional frost risk. It would allow people in the northern parts of the country to have the confidence to plant earlier, take advantage of precious growing degree days, and extend the growing season. That impact might be incalculable.

Not outside the realm of possibility ...