5 June    Ken Davis

Front passes through the IHOP region bringing extensive cloud cover and
precip, 4-5 June, 2002.  Third major frontal passage of the campaign.
(16 May, 25 May, 4 June).  Two sequences of ABL flights have been
conducted in between these frontal passages.

The first sequence was characterized by very cool air, an extremely strong
capping inversion, and west-east heterogeneity in the surface forcing.
The inversion, however, kept ABL depth remarkably homogeneous (though the
rate of warming and moistening of the ABL was not homogeneous).

The second sequence (including a NWS sounding intensive on 30 May and the
beginning of the ARM-CART sounding IOP (25 May to 15 June) featured a
similar large-scale Bowen Ratio gradient, but also smaller scale
heterogeneity brought on by heavy, patchy rainfall that occurred during
the 25 May convective period.  For example, a strong surface moisture
gradient existed along the N-S flight line that went over the Homestead
site (-100 deg, 36 min, 37 sec), with moist conditions to the south(?) due
to very intense rainfall on (26?) May.  During this sequence of flights,
ABL depths started shallow.  As the surfaces dried out ABL depth and
moisture content became extremely heterogeneous over the IHOP domain.

Convective initiation and precip forecasting missions that have been flown
during the convective intervals may also provide interesting observations
of the ABL and should not be neglected.  Of particular interest are the
daytime CI missions that are planned to begin under fair skies and observe
the development of convective storms rooted in the ABL.  These could be
seen as a natural progression from the ABL cases (stable, no deep
convection, but testing a model's ability to reproduce ABL development) to
cases where the atmosphere is less stable, but ABL development issues are
similar and coupled to the initiation of convection.  Dave Parsons also
mentioned that the 31 May ABL mission (this date might be wrong) included
data prior to a cold-core low precip event where valuable data prior to
the precip was collected by the P-3 aircraft.  (I can't find a record of
P-3 operations on this day, or a p-3 mission report that mentions this on
any other day.  We'll need a hand tracking this down.)