Transcript Highlights of Refractivity Observations by Radar (and Some More) during IHOP_2002 (Fabry)

Highlights of Refractivity
Observations by Radar (and
Some More) during IHOP_2002
Frédéric Fabry and ShinJu Park
McGill University
Montréal, Canada
A Few Definitions
IHOP_2002: International H2O Project.
Its goal: Determine how much does knowing
4-D H2O distribution help in QPF.
Refractivity (N): A quantity related to the
index of refraction (n) of air:
N = 106 (n−1) = 77.6 P/T + 373000 e/T2.
Surface N can be measured by radar up to a
range of about 50 km using ground targets.
Since over that range, P and T are (fairly)
uniform, N can be used to infer e and Td.
IHOP: Instrumentation Deployment
IHOP: S-Pol
IHOP: Ground Targets at S-Pol
Early fears that
ground targets
would be in short
supply in the
Panhandle were
unfounded,
thanks to
unburied
power/phone
lines, farms,
elevators…
Liberal
KS
OK
Hooker
Beaver
Homestead
OK
Booker
Perryton
TX
Real-Time/Default Display
Rapid moistening
Storm
60
Outflow
Wet
Diurnal cycle
(mostly)
Dry
Wet
Example: Surface Moistening, 25 May
Sunny, cool, calm morning; will warm quickly
Anomalous
propagation
echoes
Previous rain
No wind (!)
Maximizes
local effects
Example: Surface Moistening, 25 May
Previous rain
Example: Surface Moistening, 25 May
Previous rain
Example: Surface Moistening, 25 May
Previous rain
Example: Surface Moistening, 25 May
Previous rain
Example: Surface Moistening, 25 May
Previous rain
Example: Surface Moistening, 25 May
Previous rain
Example: Surface Moistening, 25 May
Previous rain
Example: Surface Moistening, 25 May
Previous rain
Example: Surface Moistening, 25 May
Previous rain
Example: Surface Moistening, 25 May
Previous rain
Example: Surface Moistening, 25 May
Previous rain
Example: Surface Moistening, 25 May
(g m-2 s-1)
360 W
Previous rain
120 W
Flux computed thanks to
a lot of crude assumptions
(too high contrast expected)
Example: Surface Moistening, 25 May
Example: Surface Moistening, 25 May
Example: Surface Moistening, 25 May
Example: Surface Moistening, 25 May
Example: Surface Moistening, 25 May
Example: Surface Moistening, 25 May
Example: Surface Moistening, 25 May
Example: Surface Moistening, 25 May
Example: Surface Moistening, 25 May
Previous rain
Note how “fragile” the moisture patch was under light winds
Contrasting Example: 29 May
72 hrs later, on a sunny day prior to 29 May
Some weak
differential
moistening
No wind again.
Maximizes
local effects
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
East winds
building up
Contrasting Example: 29 May
East winds
building up
Contrasting Example: 29 May
East winds
building up
Contrasting Example: 29 May
Moisture
boundary
East winds
building up
Contrasting Example: 29 May
Moisture
boundary
Contrasting Example: 29 May
Moisture
boundary
Contrasting Example: 29 May
Moisture
boundary
Contrasting Example: 29 May
Moisture
boundaries
Winds shift
to SE behind
2nd boundary
Contrasting Example: 29 May
Moisture
boundaries
Winds shift
to SE behind
2nd boundary
Contrasting Example: 29 May
Moisture
boundaries
Winds shift
to SE behind
2nd boundary
Contrasting Example: 29 May
Moisture
boundaries
Winds shift
to SE behind
2nd boundary
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Boundary
still lurking
Winds
shifting
to South
Contrasting Example: 29 May
Boundary
still lurking
Winds
shifting
to South
Contrasting Example: 29 May
Boundary
still lurking
Winds
shifting
to South
Contrasting Example: 29 May
Boundary
still lurking
Winds
shifting
to South
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
And now
to the SW,
and then
to the West
Contrasting Example: 29 May
And now
to the SW,
and then
to the West
Contrasting Example: 29 May
And now
to the SW,
and then
to the West
Contrasting Example: 29 May
And now
to the SW,
and then
to the West
Contrasting Example: 29 May
Boundary
makes a
comeback
Contrasting Example: 29 May
Boundary
makes a
comeback
Contrasting Example: 29 May
Boundary
makes a
comeback
Contrasting Example: 29 May
Boundary
makes a
comeback
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Contrasting Example: 29 May
Advection of
drier air on
the dry side
Contrasting Example: 29 May
Advection of
drier air on
the dry side
Contrasting Example: 29 May
King Air overflights start
Advected
boundaries
intersects
flight path
Winds are
not very
strong but
not light.
Contrasting Example: 29 May
King Air overflights in progress
Advected
boundaries
intersects
flight path
Winds are
not very
strong but
not light.
Contrasting Example: 29 May
King Air overflights in progress
Advected
boundaries
intersects
flight path
Winds are
not very
strong but
not light.
Contrasting Example: 29 May
 A strength of N maps: Provide context to ABL work
Example: Boundary Evolution
Example: Boundary Evolution
Example: Boundary Evolution
Example: Boundary Evolution
Example: Boundary Evolution
Example: Boundary Evolution
Example: Boundary Evolution
Example: Boundary Evolution
Example: Boundary Evolution
Example: Boundary Evolution
Example: Boundary Evolution
Example: Convection Initiation
Cold front approaching
Confused boundary
(more in Z than
in N) that will
sharpen with time.
Rolls-like bands
Example: Convection Initiation
Example: Convection Initiation
Example: Convection Initiation
Example: Convection Initiation
Example: Convection Initiation
Example: Convection Initiation
Example: Convection Initiation
Example: Convection Initiation
Example: Convection Initiation
Cold front approaching
Dry line
Example: Convection Initiation
Cold front approaching
Dry line
Moisture
Example: Convection Initiation
Cold front approaching
Dry line
New cells
Moisture
Example: Convection Initiation
Collision
Dry line
New cells
Moisture
Example: Convection Initiation
Collision
New cell
Dry line
New cells
Moisture
Example: Convection Initiation
New cell
New cells
Rain-induced
moist patch
Example: Convection Initiation
New cells
Rain-induced
moist patch
Example: Convection Initiation
Example: Convection Initiation
Example: Convection Initiation
Example: Convection Initiation
Another
collision
Example: Convection Initiation
Another
collision
Example: Convection Initiation
Another
collision
Example: Convection Initiation
Another
cell
Example: Convection Initiation
Another
cell
Example: Convection Initiation
Another
cell
Example: Convection Initiation
ShinJu Park (Ph.D. student)
is investigating this event.
Advices welcome.
More on this event coming…
Phenomena Observed during IHOP
Boundary layer processes:
• Convective rolls;
• Uneven moistening of BL by surface fluxes.
A variety of moisture discontinuities:
•
•
•
•
Fronts;
Drylines and other convergence lines;
Gust fronts and outflow boundaries;
More diffuse (10-20 km wide) gradients.
(Primarily) nocturnal wave phenomena:
• Nocturnal bores;
• Other waves by themselves or embedded in fronts.
Now we need to digest at least some of it…
Data Processing: IHOP “Climatology”
Broad WNW-ESE refractivity and daily N gradient observed.
Mimics (reflects?) climatological moisture gradient in the area.
Small-Scale Structure of N
Thanks to the distributed
measurements and the
near-continuous coverage
in time, one can perform
some statistics that would
be very hard to do with
other sensors.
Ex.: Systematic study of
the spatial variability of N.
How fast does N change
with distance?
Small-Scale Structure of N
Lesser variability in along-wind direction than across:
• More mixing in along-wind direction via surface friction?
• More advection-driven E-W gradients (across wind).
Small-Scale Structure of N
• Greatest variability in the afternoon until after sunset;
• Smallest just around sunrise (some wind dependence).
 Implications on representativeness of in-situ data.
Small-Scale Structure of Humidity
The amount of afternoon-time
small-scale variability changes
significantly from day to day.
Causes?
Possibilities:
• Surface-flux driven;
• BL top driven (dry air
entrainment);
• Large-scale driven.
• More?
Small-Scale Structure of Humidity
Inversion air now included in BL will dry BL
Sounding now
Sounding later
First (and only) hypothesis tested: BL top driven.
If true, small-scale variability should be well correlated
with the amount and dryness of inversion air entrained.
Small-Scale Structure of Humidity
MAD measured by surface data;
Expected drying computed from
Homestead soundings and
measured surface warming.
On days with a well-developed BL, correlation between BL
drying by entrainment and small-scale variability is high.
 Possible to predict? If yes, it could be useful to
evaluate the expected errors in BL humidity from sondes.
Spatial Structure of T, q, w
How important is the observed variability in N or humidity
for CI?
 Need to contrast with effect on CIN of heat, updrafts.
Step 1: Measure the variability of all these parameters in
the (upper) boundary layer (King Air data used).
Distance (km)
Spatial Structure of CIN
Step 2: Convert the spatial variability of all these
parameters into CIN variability.
At large scales: Temperature is the biggest player.
At small scales: Updrafts are the most important.
Moisture variability generally plays a lesser role (!)
A More Detailed Look at a CI Event
(1) Cold front
(2) Dry line
(3) Moist air
(4) Extensions of waves on the dry line in the moist air?
(5) New cells forming on these extensions
(6) Cold front-dry line collision in the making
A More Detailed Look at a CI Event
(5) New cells forming on these extensions
(6) Cold front-dry line collision in the making
(7) Cell resulting from that collision