indirect evidence of vertical humidity transport during very stable conditions at cabauw
DESCRIPTION
Indirect evidence of vertical humidity transport during very stable conditions at Cabauw. Stephan R. de Roode ( TU Delft ) & Fred C. Bosveld ( KNMI ). Stephan de Roode ( [email protected] ) Clouds, Climate and Air Quality Department of Multi-Scale Physics (TNW). - PowerPoint PPT PresentationTRANSCRIPT
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Indirect evidence of vertical humidity transport during very stable conditions at Cabauw
Stephan de Roode ([email protected])Clouds, Climate and Air Quality Department of Multi-Scale Physics (TNW)
Stephan R. de Roode (TU Delft) &
Fred C. Bosveld (KNMI)
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Stable boundary layers -Analysis of Cabauw data for the period 2001-2006
selection criterion height data fraction
I. nighttime 1m 0.50
II. clear sky 1m 0.18
III. weak wind 10m 0.08
IV. stable 5m 0.07
V. surface cooling 2m 0.05
€
SWnet <1 Wm-2
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LWnet > 40 Wm-2
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U tot < 3 ms -1
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RiB > 0
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dT
dt< 0
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Monthly mean surface energy balance during stable conditions
MonthNblocks
10 minutes
H(Wm-2)
LE(Wm-2)
-G0
(Wm-2)LWnet
(Wm-2)Res
(Wm-2)
Jan 797 -4.9 -0.7 12.0 52.2 34.6
Feb 770 -7.7 0.0 13.0 55.6 34.9
Mar 1240 -5.9 0.8 12.7 52.2 34.4
Apr 1393 -6.1 1.6 14.1 49.8 31.2
May 1150 -6.5 0.4 14.5 48.5 27.9
Jun 1154 -8.4 1.8 15.9 48.3 25.9
Jul 996 -11.0 0.9 14.3 46.6 22.2
Aug 1297 -7.8 1.3 12.5 47.0 28.1
Sep 1755 -7.7 -0.4 14.8 47.7 24.7
Oct 1047 -8.2 -0.5 11.0 48.3 28.5
Nov 945 -4.7 -2.6 12.5 49.9 30.1
Dec 1222 -4.7 -1.2 13.4 52.5 33.3
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Monthly mean surface energy balance during stable conditions
MonthNblocks
10 minutes
H(Wm-2)
LE(Wm-2)
-G0
(Wm-2)LWnet
(Wm-2)Res
(Wm-2)
Jan 797 -4.9 -0.7 12.0 52.2 34.6
Feb 770 -7.7 0.0 13.0 55.6 34.9
Mar 1240 -5.9 0.8 12.7 52.2 34.4
Apr 1393 -6.1 1.6 14.1 49.8 31.2
May 1150 -6.5 0.4 14.5 48.5 27.9
Jun 1154 -8.4 1.8 15.9 48.3 25.9
Jul 996 -11.0 0.9 14.3 46.6 22.2
Aug 1297 -7.8 1.3 12.5 47.0 28.1
Sep 1755 -7.7 -0.4 14.8 47.7 24.7
Oct 1047 -8.2 -0.5 11.0 48.3 28.5
Nov 945 -4.7 -2.6 12.5 49.9 30.1
Dec 1222 -4.7 -1.2 13.4 52.5 33.3
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Dew formation downward vertical humidity transport
Problems
- eddy correlation humidity flux at 5 m is negligibly small
- large residual in surface energy balance
Relevance
- Testing schemes (TKE, EDMF, etc) against observations
- Site used for GABLS3 case
- Humidity important for fog formation
Question
- Are the measured latent heat fluxes in accord with observed humidity tendencies from
Cabauw tower?
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Example: humidity tendencies from Cabauw tower
qsat,sfc
2m
10m
80 m
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Mean humidity tendencies (all selected SBLs)
Significant mean tendencies near the surface
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Mean humidity tendencies at 2m as a function of wind direction
Negative humidity tendency for any prevailing mean wind direction
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Tendencies of the mean humidity at 2m and the surface saturation specific humidity
Surface cooling causes downgradient humidity flux
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Mean humidity tendencies as a function of the bulk Richardson number
Tendencies even for very stable conditions
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Ditches are another local source of moisture
Courtesy Kees FloorCourtesy Adriaan Schuitmaker
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Dispersion of a passive scalar in a stable boundary layer at Cabauw
Field experiment (measuring vertical velocities with laser technique) by Petra Kroon, Harm Jonker, Adriaan Schuitmaker and others (TU Delft)
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Sources dew formation
1. Vertical turbulent transport from atmospheric column
2. Condensation of moisture evaporated from ditches
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Dew research in Wageningen (Jacobs et al.)
Wageningen dew fall corresponds to a mean latent heat flux of about 10 Wm-2
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Conclusions
1. Surface energy imbalance partly due to "missing" latent heat flux
- instrument wetting
- measurement height 5 m
- small turbulent fluctuations
2. Dew fall from
- atmospheric column
- evaporated moisture from numerous ditches
3. We expect similar dew fall as in Wageningen (about 50 km from
Cabauw)
- latent heat flux LE≈-10Wm-2 (Jacobs et al. 2006)
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Monthly mean humidity tendencies (g/kg/hr)
Month sfc 2m 10m 20m 40m 80m 140m 200m LE(Wm-
2)
Jan -0.23 -0.19 -0.07 -0.03 -0.02 -0.00 -0.01 0.00 -2.6
Feb -0.23 -0.15 -0.05 -0.04 -0.03 -0.03 -0.02 -0.04 -5.3
Mar -0.28 -0.18 -0.06 -0.04 -0.02 -0.02 -0.02 -0.02 -4.3
Apr -0.48 -0.20 -0.05 -0.02 -0.01 -0.01 -0.02 -0.02 -3.9
May -0.68 -0.22 -0.04 0.00 0.01 0.01 0.00 -0.04 -1.9
Jun -0.69 -0.17 -0.01 0.02 0.04 0.03 0.01 -0.02 1.2
Jul -0.85 -0.25 -0.08 -0.04 -0.01 0.02 -0.01 -0.06 -4.0
Aug -0.76 -0.31 -0.12 -0.09 -0.04 0.00 -0.05 -0.06 -8.3
Sep -0.71 -0.33 -0.09 -0.06 -0.03 -0.04 -0.06 -0.05 -9.4
Oct -0.64 -0.36 -0.15 -0.11 -0.08 -0.07 -0.06 -0.05 -12.5
Nov -0.49 -0.33 -0.13 -0.08 -0.05 -0.05 -0.06 -0.06 -10.5
Dec -0.27 -0.25 -0.09 -0.04 -0.03 -0.02 -0.03 -0.01 -5.4
correspondingflux