International Symposium on Tropospheric Profiling Leipzig, Germany, 15-19 September 2003

Structure and Dynamics of a Dual Bore Structure and Dynamics of a Dual Bore Event during IHOP as Revealed by Remote Event during IHOP as Revealed by Remote

Sensing and Numerical SimulationSensing and Numerical SimulationSteven E. KochSteven E. Koch

NOAA Research - Forecast Systems Laboratory

Mariusz Pagowski, James W. Wilson 1, Frederic Fabry 2, Wayne Feltz 3, Geary Schwemmer 4, Bart Geerts 5, Belay Demoz 4, Bruce Gentry 4,

David Parsons 1, Tammy Weckwerth 1, Dave Whiteman4

1 National Center for Atmospheric Research

2 Radar Observatory, McGill University3 CIMSS / University of Wisconsin

4 NASA / Goddard Space Flight Center5 Department of Atmospheric Sciences, University of Wyoming

IHOP Surface Observing Sites

Data used in Study of Two Bores on June 4, 2002

Homestead observing systems: FM-CW radar MAPR (Multiple Antenna Profiler) HARLIE (aerosol backscatter lidar) GLOW (Doppler lidar) Scanning Raman lidar (mixing ratio)

10-min AERI & 3-h CLASS data

S-POL reflectivity, radial velocity, computed refractivity

Mesonet time series, incl.refractivity calculations

Surface composite radar reflectivity and mesonetwork plots

UW King Air flight-level data

Relationship of Pressure to Temperature Fluctuations attending Bore Passage

Warming or very slight temperature changes occur with passage of both bores

Evolution of gravity currents or bores (white lines) and synoptic cold front (blue line) as seen in Radar Composite and Mesonet Data

Bore A as seen by FM-CW and HARLIE

Bore A as seen by FM-CW and MAPR

Bore B as seen by FM-CW and Raman Lidar

UWKA Flight-Level Data

Noisy data

potential temperature

vertical air velocity

mixing ratio

SE NW

Wave propagation

Bore B seen inUW King Air Dataat FL 1850 m AGL

3C cooling and 4 g/kg more moisture are found at this level behind the bore (NW).

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

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.

AERI Detection of Bores A & B

Potential Temperature

Relative Humidity

Mixing Ratio

A B

Numerical Simulations Numerical Simulations of the Boresof the Bores

Rapid decrease of refractivity in both S-POL and mesonet data due to drying caused by passage of Bore A: entrainment?

N 3.73 105 e

T 2 77.6

PT

e RH100

6.112 exp17.67T

T 243.5

Numerical Simulations of Turbulent Kinetic Energy (TKE) Generation and Mixing by Bore

Nested MM5 model (18, 6, 2, 0.666 km) initialized at 00Z 4 June 02 Initial / boundary conditions from RUC-20 model 44 vertical levels (22 below 1500 m) Three PBL experiments (all use Mellor-Yamada 2.5 closures):

BT (Burk & Thompson 1989): uses diagnostic mixing length

ETA (Janjic 1994): similar to B-T scheme but with limit upon mixing length in statically stable layers resulting in less TKE generation

QL (Kantha & Clayson 1994) offers several differences:° Improved closure for pressure covariance° Richardson number-dependent shear instability mixing term in strongly

stratified layers enhances TKE in stable layer above a well-mixed PBL° Prognostic equations for TKE and for mixing length

Physics in Numerical Simulations

Experiment Mixing Length in

PBL Scheme

Surface Fluxes

Convective

Parameterization

Microphysics

Scheme

Land Surface Model

Radiation

Scheme

BT Diagnostic Blackadar regimes

Grell-Devenyi Mixed phase Reisner

RUC RRTM

ETA Diagnostic limited in

stable layers

Eta

Method

Kain-Fritsch Mixed phase Reisner

5-layer soil

RRTM

QL Kantha-Clayson

Eta method

Kain-Fritsch Mixed phase Reisner

5-layer soil

RRTM

q2

t

z

lqq2

z

2 u w

uz

2 v w vz

2g w v 2q3

l

BT 666-m simulation of TKE (shaded), 2D circulation vectors, and potential temperature 0730 – 0930 UTC: Bore B

BT and ETA results both show less mixing than QL results because shorter mixing length creates more TKE dissipation

Conclusions

Two bores or solitons observed as fine lines in S-POL reflectivity and by remote sensing 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 (seen in AERI data and UWKA data for Bore B) occurred as a likely result of adiabatic lifting.

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. It appears to have been weakening.

Numerical simulations are being used to understand actual bore generation mechanism, solitary wave dynamics, and why drying (reduction of refractivity) only occurs at certain times. Bore forcing mechanisms are very sensitive to model physics, and details concerning entrainment and turbulence depend upon PBL parameterization – suggesting need for LES studies.