Flight plan: To investigate stratospheric intrusions the flight plan is to cross the PV-streamer at two, or preferably three different levels some kilometers below the tropopause, right at the tropopause and two or three kilometer above the tropopause in order to measure potential vorticity with in situ aircraft sensors and ozone with high spatial resolution. At the uppermost flight altitude ranging from 40,000 to 50,000 feet MSL a water vapor DIAL looking vertically downwards has to be used to measure the horizontal and vertical structure of the water vapor field with high spatial resolution. The release of dropsondes is desirable in order to obtain sound data for the meteorological background fields. Simultaneous measurement of ozone is desirable since ozone is an indicator of stratospheric air possessing high potential vorticity. The presents of such dry air extending into the troposphere appears as a dark band of the water vapor satellite image. The maximum flight time for this mission amounts to about 3-4 hours in total without ferry. The distance of each flight leg crossing the PV-streamer is about 700 km.
Instrumentation: HIAPER should be equipped with a downward- looking water vapor DIAL capable to measure low water vapor mixing ratios at ppm level. In addition dropsondes and in situ sensors for u,v,w, T, and ozone measurements are necessary.