from the Greek meso-
, meaning "medium" or "moderate": a scale in between the microscale
1. In the spatial domain, a loosely-defined scale encompassing all phenomena that occur between 2km and hundreds of kilometers. Oceanographers use a lower resolution but a larger area; meteorologists are interested in a slightly smaller area with higher resolution. Because ocean and weather effects drive each other, the definition of "mesoscale" blurs at the interfaces between the disciplines.
2. In the time domain, a loosely-defined scale encompassing all phenomena that occur over a day through a few weeks. Again, oceanographers are interested in a slower class of activity because ocean conditions change more slowly than atmospheric conditions.
Meteorologists consider severe storms to occur on the mesoscale both spatially and chronologically. Mesoscale weather measurements are aggregated from grids of local doppler radar systems, satellite imagery, and ground-based temperature and humidity measurements. Overlaying this data on terrain features permits the prediction of tornadoes and large severe storms. Geostationary satellites can also detect lightning flashes; flash rate can be used as an indicator of impending tornadoes. Mesoscale winds carry weather patterns from place to place, and are influenced by large patches of differently-colored terrain (snow and desert reflect sunlight, dark foliage and blue water absorb it).
Oceanographers compile their mesoscale information from space-based altimeters to measure the sea surface height and wave height; a combination of buoys and space-based infrared imagers to measure sea surface temperature; and spectrometers and buoys to measure ocean salinity. Salinity allows precise determination of the coefficient of thermal expansion of a column of water. With accurate bathymetry and historical data for the temperature at the bottom, temperature profile and sea surface height can be integrated to determine the total thermal energy in a given column of water. A mesoscale "column" might measure 20-200km in diameter, and extend from 4km to 10km below the ocean surface. Thermal energy measurements can be mapped to latitude-longitude pairs and used to predict formation and strengthening of hurricanes and other maritime storms. Thermal energy and temperature/depth measurements help to characterize mesoscale undersea currents, which can impact the precision of sonar systems.