Analysis of PBL Turbulent and Non-turbulent Fluxes

M. Hicks1, S. Kang2, B. Demoz1, E. Joseph1,

1 Howard University, Washington, DC, USA2 UCAR, Boulder, CO, USA

Outline

• Overview

• HUBC Characteristics

• Methodology

• Preliminary Results

• Future Work

Motivation• Previous (observational and model) studies have

suggested that strong heterogeneous CBLs can produce non-turbulent fluxes at scales with magnitudes comparable to turbulent fluxes (Kang and Davis 2008, Kang et al. 2007, LeMone et al. 2002, Mahrt et al. 1994a,b)

• Implying turbulent theory may fail under these conditions

From (Kang, 2008)

Objective & Purpose

• Objective– Examine the importance of non-turbulent to turbulent

heat and moisture transport in a heterogeneous CBL.• Look at the importance of presenting a proper timescale

• Purpose– Analyze the non-turbulent and turbulent

characteristics of fluxes at HUBC through tower observation

• No one has used tower observations to examine non-turbulent flux exchanges

Howard University Beltsville, MD Research Campus

http://meiyu.atmphys.howard.edu/beltsville/inde3.html

• Site Characteristics – Located 12 miles NE of Washington, DC– Heterogeneous landscape – Experiences a wide range of water vapor and aerosol

concentrations

HU Beltsville Campus

Methodology1. Apply FFT and MR Spectra analysis to find

timescale, , needed to separate turbulent and non-turbulent fluxes

– The traditional 30 minute may not be sufficient in eliminating non-turbulent fluxes for heterogeneous cases. (Vickers and Mahrt 2003)

2. Examine the contribution of non-turbulent fluxes to total flux

XTot=X-<X>, XNT=[X]-<X>, XT=X-[X]

Case Study

Preliminary Results

• Vertical velocity energy pass 100 sec is small as expected

• WVMR has strong energy exchanges around 1000 sec

• A timescale less much less than 30mins is needed to separate T and NT fluxes

• The NT fluxes are not very strong

Separating Fluxes

•Green~ Instantaneous timeseries

•red ~mesoscale averaged timeseries, [X]

• blue ~domain averaged timeseries,<X>

X’=X-<X>

XNT=[X]-<X>,

XT=X-[X]

Preliminary Results

The intensity of WT transport of non-turbulent heat is clearly seen

The lack of intensity from pure non-turbulent mesoscale flux is seen

Summary

• We showed that a 30 minute timescale average may not always represent pure turbulence.– It is believed that including non-turbulence

can give a bias to CBL parameterizations

• Interscale flux maybe able to explain intense moments of non-turbulence

Future Work

• Make Further progress with analysis surface layer CBL turbulent and non-turbulent fluxes

• Expand diagnosis to examine flux characteristics of the well mixed and inversion layers of the heterogeneous CBL.– Summer 2010 HUBC Field Campaign

• Tethersonde Balloon• HURL ~1min• MDE wind profiler ~1min• Microwave Radiometer (r,T) ~2min• Leosphere lidar ~10s• Radiosondes

Acknowledgements

• I thank all supporters of this work, – Dr. Songlak Kang for suggestions– Dr. Belay Demoz – Dr. Everette Joseph– Dr. Demetrius Venable and HURL team – NCAS for support

Backup Slides

Overview• Why Study PBL Fluxes???

– Fluxes play a critical role in the development of the height of the PBL

• Operational obs of PBL heights are not taken to validate forecast model parameterizations

– Models at time can significantly over or under estimate PBL heights

From Kang et al., 2007

Monin-Obukov Similarity theory

Businger et al. 1971

Kang and Davis 2008

Weak heterogeneous case

Strong heterogeneous case

Turbulent flux

Interscale flux

Non-Turbulent flux

Preliminary Results

• Green line is instantaneous timeseries, X

• red line is mesoscale averaged timeseries, [X]

• blue line is domain averaged timeseries,<X>

F(sec-1)

XNT=[X]-<X>, XT=X-[X]

07092007

F(sec-1)