Estimation of boundary layer humidity fluxes and statistics from airborne differential absorption lidar (DIAL)

Christoph Kiemle, Gerhard Ehret, Andreas Giez, Kenneth James Davis, Donald H. Lenschow, Steven P. Oncley

Research output: Contribution to journalArticle

50 Citations (Scopus)

Abstract

The water vapor differential absorption lidar (DIAL) of the German Aerospace Research Establishment (DLR) was flown aboard the National Center for Atmospheric Research (NCAR) Electra research aircraft during the Boreal Ecosystem-Atmosphere Study (BOREAS). The downward looking lidar system measured two-dimensional fields of aerosol backscatter and water vapor mixing ratio in the convective boundary layer (CBL) and across the CBL top (z,i). We show a case study of DIAL observations of vertical profiles of mean water vapor, water vapor variance, skewness, and integral scale in the CBL. In the entrainment zone (EZ) and down to about 0.3 zi the DIAL observations agree with in situ observations and mixed-layer similarity theory. Below, the water vapor optical depth becomes large and the DIAL signal-to-noise ratio degrades. Knowing the water vapor surface flux and the convective velocity scale w* from in situ aircraft measurements, we derive entrainment fluxes by applying the mixed-layer gradient (MLG) and mixed-layer variance (MLV) methods to DIAL mixing ratio gradient and variance profiles. Entrainment flux estimates are sensitive to our estimate of zi. They are shown to be rather insensitive to the input surface flux and to the DIAL data spatial resolution within the investigated range. The estimates break down above about 0.9 zi as the flux-gradient and flux-variance relationships were developed to describe the large-scale mixing in the mid-CBL. The agreement with in situ entrainment flux estimations is within 30% for the MLV method. On a flight leg with significant mesoscale variability the entrainment flux turns out to be 70% higher than the in situ value. This is in good agreement with the fact that large-eddy simulations (LES) of mean water vapor profiles and variances, upon which the MLG and MLV methods are based, do not include mesoscale variability. The additional water vapor variance from mesoscales may then lead to the overestimate of the flux. Deviations from the in situ observations may also be due to poor LES resolution of small-scale mixing in the EZ, similarly coarse resolution of the DIAL data, or a capping inversion in the LES model (8 K) which is significantly stronger than the observed inversion (3-4 K).

Original languageEnglish (US)
Pages (from-to)29189-29203
Number of pages15
JournalJournal of Geophysical Research Atmospheres
Volume102
Issue number24
StatePublished - Dec 26 1997

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differential absorption lidar
lidar
Optical radar
water vapor
Steam
humidity
boundary layers
Atmospheric humidity
Boundary layers
statistics
boundary layer
Statistics
entrainment
Fluxes
mixed layer
convective boundary layer
large eddy simulation
Large eddy simulation
aircraft
gradients

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

Cite this

Kiemle, Christoph ; Ehret, Gerhard ; Giez, Andreas ; Davis, Kenneth James ; Lenschow, Donald H. ; Oncley, Steven P. / Estimation of boundary layer humidity fluxes and statistics from airborne differential absorption lidar (DIAL). In: Journal of Geophysical Research Atmospheres. 1997 ; Vol. 102, No. 24. pp. 29189-29203.
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abstract = "The water vapor differential absorption lidar (DIAL) of the German Aerospace Research Establishment (DLR) was flown aboard the National Center for Atmospheric Research (NCAR) Electra research aircraft during the Boreal Ecosystem-Atmosphere Study (BOREAS). The downward looking lidar system measured two-dimensional fields of aerosol backscatter and water vapor mixing ratio in the convective boundary layer (CBL) and across the CBL top (z,i). We show a case study of DIAL observations of vertical profiles of mean water vapor, water vapor variance, skewness, and integral scale in the CBL. In the entrainment zone (EZ) and down to about 0.3 zi the DIAL observations agree with in situ observations and mixed-layer similarity theory. Below, the water vapor optical depth becomes large and the DIAL signal-to-noise ratio degrades. Knowing the water vapor surface flux and the convective velocity scale w* from in situ aircraft measurements, we derive entrainment fluxes by applying the mixed-layer gradient (MLG) and mixed-layer variance (MLV) methods to DIAL mixing ratio gradient and variance profiles. Entrainment flux estimates are sensitive to our estimate of zi. They are shown to be rather insensitive to the input surface flux and to the DIAL data spatial resolution within the investigated range. The estimates break down above about 0.9 zi as the flux-gradient and flux-variance relationships were developed to describe the large-scale mixing in the mid-CBL. The agreement with in situ entrainment flux estimations is within 30{\%} for the MLV method. On a flight leg with significant mesoscale variability the entrainment flux turns out to be 70{\%} higher than the in situ value. This is in good agreement with the fact that large-eddy simulations (LES) of mean water vapor profiles and variances, upon which the MLG and MLV methods are based, do not include mesoscale variability. The additional water vapor variance from mesoscales may then lead to the overestimate of the flux. Deviations from the in situ observations may also be due to poor LES resolution of small-scale mixing in the EZ, similarly coarse resolution of the DIAL data, or a capping inversion in the LES model (8 K) which is significantly stronger than the observed inversion (3-4 K).",
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Estimation of boundary layer humidity fluxes and statistics from airborne differential absorption lidar (DIAL). / Kiemle, Christoph; Ehret, Gerhard; Giez, Andreas; Davis, Kenneth James; Lenschow, Donald H.; Oncley, Steven P.

In: Journal of Geophysical Research Atmospheres, Vol. 102, No. 24, 26.12.1997, p. 29189-29203.

Research output: Contribution to journalArticle

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T1 - Estimation of boundary layer humidity fluxes and statistics from airborne differential absorption lidar (DIAL)

AU - Kiemle, Christoph

AU - Ehret, Gerhard

AU - Giez, Andreas

AU - Davis, Kenneth James

AU - Lenschow, Donald H.

AU - Oncley, Steven P.

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N2 - The water vapor differential absorption lidar (DIAL) of the German Aerospace Research Establishment (DLR) was flown aboard the National Center for Atmospheric Research (NCAR) Electra research aircraft during the Boreal Ecosystem-Atmosphere Study (BOREAS). The downward looking lidar system measured two-dimensional fields of aerosol backscatter and water vapor mixing ratio in the convective boundary layer (CBL) and across the CBL top (z,i). We show a case study of DIAL observations of vertical profiles of mean water vapor, water vapor variance, skewness, and integral scale in the CBL. In the entrainment zone (EZ) and down to about 0.3 zi the DIAL observations agree with in situ observations and mixed-layer similarity theory. Below, the water vapor optical depth becomes large and the DIAL signal-to-noise ratio degrades. Knowing the water vapor surface flux and the convective velocity scale w* from in situ aircraft measurements, we derive entrainment fluxes by applying the mixed-layer gradient (MLG) and mixed-layer variance (MLV) methods to DIAL mixing ratio gradient and variance profiles. Entrainment flux estimates are sensitive to our estimate of zi. They are shown to be rather insensitive to the input surface flux and to the DIAL data spatial resolution within the investigated range. The estimates break down above about 0.9 zi as the flux-gradient and flux-variance relationships were developed to describe the large-scale mixing in the mid-CBL. The agreement with in situ entrainment flux estimations is within 30% for the MLV method. On a flight leg with significant mesoscale variability the entrainment flux turns out to be 70% higher than the in situ value. This is in good agreement with the fact that large-eddy simulations (LES) of mean water vapor profiles and variances, upon which the MLG and MLV methods are based, do not include mesoscale variability. The additional water vapor variance from mesoscales may then lead to the overestimate of the flux. Deviations from the in situ observations may also be due to poor LES resolution of small-scale mixing in the EZ, similarly coarse resolution of the DIAL data, or a capping inversion in the LES model (8 K) which is significantly stronger than the observed inversion (3-4 K).

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