Upper-Level Charts
Constant Pressure (or Isobaric) Charts - General Characteristics
(southern) hemisphere, high-altitude balloonist, facing into his/her (1) Constant-height lines (and isobars) run, on the average, from west to east, parallel
to the earth's circles of constant latitude. [The pressure gradient force is always
perpendicular to the local direction of the constant-height lines (and isobars), in
the direction of decreasing height (and pressure).](2) Heights (and pressures) tend to decrease with increasing latitude.
(3) Isotherms are roughly parallel to constant-height lines (and isobars).
(4) Temperatures tend to decrease with increasing latitude.
(5) Wind direction tends to be parallel to the constant-height lines (and isobars and
isotherms), with an average direction from west to east.(6) A northern
direction of motion, would have low pressure to the left (right) and high pressure
to the right (left).(7) The stronger the pressure gradient force (indicated by a decreasing separation
between adjacent constant-height lines [or isobars]) the stronger the winds.
Wind flow which is roughly from west-to-east is called "zonal flow." Wind flow which is roughly north-to-south or south-to-north is called "meridional."
Regions where the isotherms and constant height lines (or isobars) are nearly parallel are called "barotropic." Region where the isotherms and constant-height lines (or isobars) intersect are called "baroclinic." Weather conditions are likely fairly stable in barotropic regions and changing in baroclinic regions.