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Multi-scale Analyses of Moisture and Winds during
the 3 and 9 June IHOP Low-Level Jet Cases
Edward Tollerud, Fernando Caracena, Adrian
Marroquin, Brian Jamison, and Steve Koch NOAA
Forecast Systems Laboratory and Cooperative
Institute for Research in the Environmental
Science (CIRES)
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Two IHOP Morning Low Level Jet (LLJ) Missions On
the mornings of June 3 and June 9, aircraft
missions were flown in the IHOP domain to observe
LLJ circulations and moisture structure. The
primary instrumentation included extra standard
radiosonde launches, aircraft-launched
dropsondes, and airborne lidar wind and moisture
measurements from the DLR Falcon and Learjet.
Using data observed from these platforms it is
possible to describe the moisture structure and
transport in the LLJ in unprecedented detail and
at multiple scales. We describe the observations
made in these missions and the flight tracks
designed to observe them. Some initial model
results from a detailed MM5 run are also
discussed. Sections of dropsonde and lidar
moisture and wind observations are shown.
Finally, an application of detailed dropsonde
profiles to assessment of radiosonde processing
accuracy are presented.
Description and Comparisons of LLJ Wind and
Moisture Structure vis-à-vis Mission Science
Objectives HRDL observations of windspeed normal
to the Falcon flight track during the June 9
mission, combined with simultaneous DIAL
measurements of specific humidity, will provide
highly-resolved estimates of transport by the
LLJ. When compared with computations using
dropsonde measurements at a larger scale (roughly
60 km separation of observations) and with
radiosonde observations made at even larger
scales, the lidar flux computations can begin to
address questions about the utility of moisture
measurements at these fine scales. Specifically,
the presence of correlations of the windfields
with the moisture fields at scales below that
resolved by the operational network of
radiosondes and profilers may be determined.
Model runs that incorporate research observations
by dropsondes will also be compared with existing
runs that do not to get another assessment of the
impact of mesoscale observations on forecasts of
LLJ transport.
DIAL (onboard lidar, DLR Falcon) observations of
specific humidity. Compare with
dropsonde-observed section below. Anomalous
rectangular regions near east end of section
suggest cloud contamination.
Jet Core Dropsonde Profile, June 9
DLR Falcon Dropsonde Sections Along the Northern
Leg of the June 9 Flight Track
LASE Data from DC-8
LLJ Mission Forecasting Issues involved with
forecasting LLJ occurrences for IHOP mission
planning are revealed in the two RUC 10 km 12h
forecasts for 1200 UTC June 9 shown above and to
the right. A jet with good moisture that met
windspeed criterion was suggested in the surface
fields in central and western KS and OK.
Secondly, for optimum performance of the lidar
sensors on the Falcon, essentially cloud-free
conditions were required. The forecast of
cloudtops (above) suggested possible trouble, and
indeed some slight cloud contamination was
encountered.
Windspeed (m/s). The core of the LLJ is indicated
near the eastern end of the flight leg at a
pressure of about 820 mb.
Mixing Ratio (r) in g/kg. The depth of the moist
boundary layer increases eastward. The
mid-boundary layer dryness at the extreme east
end is relected also in the DIAL sections above
Moisture Transport across the northern side of
the flight box as given by v . r, where v is the
wind component transverse to the flight leg..
Terra Modis Satellite Image, 1641 UTC 3 June 2002
June 9 Aircraft Tracks and Dropsonde Observation
Locations
Radiosonde Processing and IHOP Observations
Dropsonde data taken during Ihop has allowed us
to see the vertical structure of low-level jets
that developed over the area of the field
experiment with a vertical sample interval better
than 5 m. The terminal speeds of these dropsondes
was about 7 m/s and the wind sample rate was 0.5
s . Contrast these values with those of
radiosondes, which rise at 5 m/s and wind samples
are taken every 6 s . During IHOP, an archaic
procedure used by NWS in coding transmitted wind
data described by Doswell (http//www.cimms.ou.edu
/ doswell/NWSwinds/NWS_Winds.html), futher
degraded wind measurements, resulting in a
corresponding degradation of initial wind data in
the Eta model. The figure shows a comparison of
two vertical wind profiles (80 km Eta initial
field, dashed and dropsonde data, solid) taken at
the first dropsonde release point on 1104 UTC 3
June 2002. The Eta wind profile was obtained from
the grid point nearest to the dropsonde location,
and includes the boundary layer level output as
well. Note that the boundary layer resolution of
the model is not manifest in the initial fields
because the model has been fed coarse, "minute"
wind information from the radiosondes. The
coarser radiosonde wind data has resulted in a
15-20 maximum wind error in the wind speed at
and below the level of maximum winds. The effect
is magnified in the horizontal moisture
transport, which is computed from the product of
the mixing ratio and wind speed (profiles shown
in bottom figure). The sharp peak in vertical
profile of moisture transport by the LLJ is
located at about 300 m above ground level (AGL).
Looking at the structure of the Eta wind profile,
one can see that there would be a large error in
moisture transport below 800 m AGL.
S-POL Radar Doppler Velocities
Jet Core Dropsonde Profile
MODELING STUDY, JUNE 3 CASE The RAMS model was
initialized with LAPS analyses fields for 1500
UTC 3 June 2002 over the IHOP area with lateral
boundary fields taken from the RUC20 model. For
verification, we use the NOWRAD patterns for 3
June 2002, valid at 1800 UTC shown below. The
model was run in a two-nested grid configuration
with the innermost grid spacing of 4 km and an
external grid of 12 km. A horizontal cross
section of wind vectors, isotachs (red), and
precipitation (black) from a 3-h forecast is
shown at the right. The initial fields are from
LAPS analysis with conventional data (no IHOP
observations) and include the "hot start"
diabatic initialization procedures (which
includes moisture and consistent vertical
velocities) to describe
the initial cloud field. The wind barbs and
isotachs in the figure seem to suggest that the
LLJ splits into two branches (upper right of
figure), with one branch feeding the convective
activity over Kansas and the other continuing to
the northeast (upper right of figure). The
precipitation pattern correlates with the NOWRAD
radar shown to the lower left.
NAST Lidar data Proteus aircraft
June 3 Aircraft Tracks and Dropsonde Observation
Locations
NOWRAD radar mosaic valid 1800 UTC 3 June 2002.
Notice the radar pattern across New Mexico-Texas
border, which suggests convective activity
forecasted by RAMS