Stratospheric Intrusions are when stratospheric air dynamically
decends into the troposphere and may reach the surface, bringing with it high concentrations of ozone which may be harmful to some people. Stratospheric
Intrusions are identified by very low tropopause heights, low heights of the 2 potential vorticity unit (PVU) surface, very
low relative and specific humidity concentrations, and high concentrations of ozone. Stratospheric Intrusions commonly follow
strong cold fronts and can extend across multiple states. In satellite imagery, Stratospheric
Intrusions are identified by very low moisture levels in the water vapor channels (6.2, 6.5, and 6.9 micron). Along with the dry air,
Stratospheric Intrusions bring high amounts of ozone into the tropospheric column and possibly near the surface. This may be
harmful to some people with breathing impairments. Stratospheric Intrusions are more common in the winter/spring months and
are more frequent during La Nina periods. Frequent or sustained occurances of Stratospheric Intrusions may decrease
the air quality enough to exceed EPA guidelines.
NCEP Global Forecast System model (GFS) analyses and forecasts of certain variables in the
upper troposphere/lower stratosphere (UTLS) can identify current and future Stratospheric Intrusion events. GFS analysis
and forecast plots are generated each day from the 00Z cycle at 12 hour intervals out to 5 days (f120).
Stratospheric Intrusions can be identified as red colored areas on GOES RGB Air Mass imagery on the
RAMMB/CIRA "SLIDER" web page.