Multi-Platform Observations of a Bore Event on 4 June during IHOP

IHOP Science Meeting24-26 March 2003

Multi-Platform Observations of a Bore Event on 4 June during IHOP

Steven E. Koch

Frederic Fabry, Bart Geerts, Tammy Weckwerth,

James Wilson, Dave Parsons, and Wayne Feltz

Data used in Study of this Bore Event

S-POL reflectivity, (radial velocity), refractivity

Surface mesoanalysis plots

Mesonet time series, incl.refractivity calculations

AERI & CLASS thermodynamic structure evolution

FM-CW, HARLIE, MAPR, (RAMAN lidar), (GLOW)

UW King Air flight-level data

High-resolution MM5 simulations (next talk)

Computation of Refractivity from Surface Data

17.676.112 exp

100 243.5

o

o

T CRHe

T C

52

PRESSURE MOISTTERM TERM

77.6 3.73 10O O

P hPa e hPaN

T K T K

Refractivity

Vapor Pressure

IHOP Science Meeting24-26 March 2003

BORE A

S-POL: 0430 – 0730 UTC

Surface Analysis at 0500 UTC

FM-CW and HARLIE Displays of Bore A

FM-CW and MAPR Displays of Bore A

Bore A at Verles (0520 Z)

Bore A at Rusty Tank (0530 Z)

Bore A at Playhouse (0552 Z)

Bore A at Lincolns (0635 Z)

IHOP Science Meeting24-26 March 2003

BORE B

S-POL: 1000 – 1200 UTC

Surface Analysis at 1000 UTC

FM-CW Display of Bore B

UWKA Flight-level data

FM-CW and MAPR Displays of Bore B

temperature

potential temperature

vertical air velocity static pressure

(u,v)

theta-e

mixing ratio

SE NW

Wave propagation

UW King Air DataFL 1850 m AGL

KA penetrated solitary waves at the top of the bore. The waves are ranked in amplitude (as in FM-CW).

3C cooling and 4 g/kg more moisture found at this level behind the bore (NW) – unlike the drying/warming seen in SPOL near-sfc refractivity.

Vertical motions are in phase quadrature with theta and u/v, as in a typical gravity wave, but strangely out of phase with pressure fluctuations.

Pressure variations are mainly a response of the aircraft to the vertical motion field. Mean 1.2 m/s updraft over 30 sec produces 35 m ascent or 3.5 mb hydrostatic pressure decrease.

Bore B at Verles (0942 Z)

Bore B at Rusty Tank (1020 Z)

Bore B at Playhouse (1022 Z)

Bore B at Lincolns (1100 Z)

AERI and ISS Detection of Bores A & B

Potential Temperature

Relative Humidity

Conclusions

Two bores or solitons observed as fine lines in S-POL reflectivity and by FM-CW, MAPR, ISS, Mesonet, UWKA data systems:

Bore A occurred along an outflow boundary that propagated eastward from the Oklahoma Panhandle

Bore B occurred along a cold front enhanced by postfrontal convection in northwestern Kansas

Solitary waves developed to the rear of each leading fine line atop a 700 – 1000 m deep surface stable layer. Depth of stable layer increased by 0.6 km with passage of leading wave in bores A and B.

Solitary wave characteristics: periodicity = 15 – 30 min, horizontal wavelength = 10 – 20 km, phase speed = 11.4 – 12.6 m/s. Waves exhibited amplitude-ordering (leading wave always the largest one).

Conclusions

Pronounced reduction in refractivity due to drying in surface layer occurred when the leading pressure jump was relatively strong.

Cooling & moistening aloft occurring with passage of both bores a likely result of adiabatic lifting (seen in AERI data and UWKA data for Bore B). UWKA pressure data is confusing.

Bore A appears to have been a soliton on a surface inversion layer. Bore B occurred at a higher elevation of 1.2 km as the inversion had lifted by that time, but problems remain with FM-CW data interpretation. It appears to have been a weakening soliton.

Need to understand better why drying (reduction of refractivity) only occurs at certain times. Analysis of MAPR, GLOW, & SPOL wind data, additional mesonet data, and UWKA data will be needed.