Past IEM Features tagged: flux
Above freezing temperatures and sunshine helped to melt some of our snow in Iowa on Monday. The featured chart is of latent heat flux from the one of the NLAE flux sites since the first of the year. Latent heat is a measure of the energy being transferred from the surface to the atmosphere as the result of evaporation or sublimation of water. In this context, a positive number is a transfer of energy to the atmosphere. The large spike on Monday is certainly indicative of the enhanced snow melt, sublimation, and evaporation that was occuring. These processes require heat, so it acts to slow the surface air heating rate as energy is consumed to change the phase of water. This is a big reason why near surface air temperatures can not get too warm with snow on the ground.
The featured chart is a time series of local noon measured short wave radiation this year at one of the flux sites operated by the National Laboratory for Agriculture and the Environment. "Short wave" is a term used to describe the wavelengths at which most of the sun's radiated energy is found at. The top chart shows the energy arriving from the sun (downwelling) and the amount reflected by the surface (upwelling). The ratio between these two values is called "albedo" and is presented in the bottom chart. The last two days saw a dramatic change in albedo with the arrival of snow. This is one of the main reasons why our weather gets cold when it snows as the snowcover is a very efficient reflector of the sun's energy. The chart also shows some nice growing season effects as the corn canopy expands and harvest occurs in the fall.
Tags: albedo flux