Upper Level Low - Meteorological Physical Background by ZAMG and
FMI Upper Level Lows are closed cyclonically circulating eddies
in the middle and upper troposphere. They are sometimes also
called "cold drops", because the air within an Upper Level Low
is colder than in its surroundings. The development of a typical
Upper Level Low goes through four stages, during which a bottom
of an upper trough is detached from the main stream, until it
finally fills up or merges with another trough: - Upper level
trough - Final stage 1. Upper Level Trough stage The
prerequisite of the forming of the Upper Level Low are unstable
waves within the main stream, where the temperature wave is
behind the geopotential wave. - There is cold advection within
the trough and warm advection on the ridge of the geopotential
wave. - The vertical axis of the trough has a backward-oriented
inclination with height. - The amplitudes of the waves increase;
the wavelenght can decrease. Cyan: 500 hPa geopotential height,
green: 500 hPa tempera