# Results for case Diurnal evolution of an atmospheric boundary layer

Code: Code_Saturne

Version: 2.0-rc2

Authors: M. Milliez

## Method and Numerical Options

• Atmospheric flows:
• dry atmosphere (transport of potential temperature in a dry atmosphere, production term in the tke equation and wall boundary conditions adapted to the stratification of the atmosphere)
• reading of a meteorological data file
• Unsteady flow, gravity with improved hydrostatic pressure interpolation.

## Models

%$k-\varepsilon$%

## Mesh

Horizontally periodic column mesh, with an horizontal resolution of 100m, 20 vertical levels between 0 and 2000 m with a vertical resolution from 10 to 50m.

## Boundary conditions

• Lateral: periodic
• Top: symmetry
• Ground: rough wall, with dynamical and thermal roughness lengths equal to 1.2 mm. The ground temperature is imposed and taken from the measurements.

## Physical forcing

The short-wave and long-wave radiative forcing were taken into account by adding additional radiative source terms (ustssn.f90). Those radiative source terms were extracted from a numerical simulation with the atmospheric model Mercure_Saturne.

#### Forcing with the geostrophic wind

The geostrophic wind was computed with a one-hour time step from Yamada and Mellor (1975) method. The Coriolis parameter is equal to %$f = -0.826 10^{-4}.rad.s^{-1}$% (latitude: 34°30' S). The forcing with the geostrophic wind was taken into account by adding source terms in the NS equation (ustsns.f90).

#### Potential temperature relaxation

The potential temperature was relaxed from the level 1600 m to the level 2000 m to the reference potential temperature profile, computed from the meteorological profile (ustssc.f90).

## Results

The simulation results were compared to the measurements for the day 33 and the night 33/34.

#### Potential temperature

The numerical results are in good agreement with the measurements: the model is able to simulate the development of the daytime convective boundary layer and gives a good estimation of the ABL height at 1800 LT. During the night, the measurements show a warming of the air between 1000 and 1500m. This effect can be explained by larger scale advection of warm air, which is not taken into account in standard 1D models. Thus, the simulated night time profiles show a residual layer which remains mixed and cools down by infra-red emission. The radiative cooling enables the model to accurately simulate the formation of the stable ABL during the night, which is nevertheless underestimated.

• Daytime evolution of the modelled potential temperature profile:

• Daytime evolution of the measured potential temperature profile:

• Nighttime evolution of the modelled potential temperature profile:

• Nighttime evolution of the measured potential temperature profile:

#### Wind speed

The the simulated wind speed profiles are in good agreement with the measurements. The disagreement is weak for the daytime profiles, although an underestimation of the maximum wind speed at 1500 and 1800 LT. The model accurately simulates the night time wind speed evolution: taking into account the radiative cooling enables the night time stable boundary layer to correctly develop, with a good simulation of the low level jet. The maximum wind speed at 0300 LT is slightly underestimated (12 %$ms^{-1}$% instead of 13 %$ms^{-1}$%) as well as the vertical extension of the low level jet, which can be explained by the underestimation in the development of the night time stable BL.

• Daytime evolution of the modelled wind speed profile:

• Daytime evolution of the measured wind speed profile:

• Nighttime evolution of the modelled wind speed profile:

• Nighttime evolution of the measured wind speed profile:

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Topic attachments
I Attachment Action Size Date Who Comment
png rayon.png manage 56.4 K 2010-09-17 - 09:27 UnknownUser Short-wave and long-wave radiative forcing
png tpotj33-20rc2.png manage 143.1 K 2010-09-16 - 13:53 UnknownUser Daytime evolution of the modelled potential temperature profile
png tpotj33_mesures.png manage 165.9 K 2010-09-16 - 14:01 UnknownUser Daytime evolution of the measured potential temperature profile
png tpotj34-20rc2.png manage 143.1 K 2010-09-16 - 14:10 UnknownUser Nighttime evolution of the modelled potential temperature profile
png tpotj34_mesures.png manage 165.9 K 2010-09-16 - 14:11 UnknownUser Nighttime evolution of the measured potential temperature profile
png tsol_mesures.png manage 14.4 K 2010-09-14 - 14:14 UnknownUser Diurnal evolution of the ground temperature
png ventj33-20rc2.png manage 143.6 K 2010-09-16 - 14:11 UnknownUser Daytime evolution of the modelled wind speed profile
png ventj33_mesures.png manage 166.2 K 2010-09-16 - 14:12 UnknownUser Daytime evolution of the measured wind speed profile
png ventj34-20rc2.png manage 143.6 K 2010-09-16 - 14:13 UnknownUser Nighttime evolution of the modelled wind speed profile
png ventj34_mesures.png manage 166.2 K 2010-09-16 - 14:18 UnknownUser Nighttime evolution of the measured wind speed profile
Topic revision: r16 - 2017-05-19 - 03:37:43 - AllenZhang
CfdTm Web
23 Aug 2019

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