1. Convective and orographically-induced precipitation study
The simulation of a deep convective cloud in complex orography:
the 15 July 2007 case from COPS
Ralph Burton, Alan Gadian, Alan Blyth, Stephen Mobbs National Centre for Atmospheric Science, University of Leeds, UK contact:
WRF modelling: sensitivity to boundary-layer and land-surface schemes
COPS
This study presents a sensitivity test consisting of four runs. Features common to all runs are contained in Table I; differences between runs are described in Table II.
Convective and orographically-induced precipitation study
Table I
Table II
Numerical and dynamical parameters
Nest number 1 2
Grid sizes
and resolution
550x550 x 50 vertical levels, 3.6km
301x241 x 50 vertical levels, 1.2km
Time step
18s 6s
Cumulus
parametrisation
None
Microphysics
Morrison
Radiation (SW)
Dudhia
Radiation (LW)
RRTM
Run name
BL scheme
Land surface
Comments
THERM_YSU
YSU
Thermal diffusion
Very shallow, very isolated cloud.
THERM_MYJ
MYJ
Very shallow cloud.
NOAH_YSU
NOAH LSM
NOAH_MYJ
Deep cloud extending to approx 12km in altitude.
Isolated, deep cloud formed on the 15th July from 13-16Z. This was perhaps the only instance of such a cloud during the whole COPS experiment. The ability of a numerical model (WRF) to simulate this cloud is the subject of this study.
Photo from the Science Director Summary,
Domains used in the WRF simulation. The outer domain is at 6.1km resolution; the inner domain at 2.1km resolution.
Location of the COPS field phase. Map taken from the COPS brochure [1].
For an overview of the COPS campaign see [2].
All runs initialised at 0Z 15th July with GFS analyses
Vertical velocities and wind vectors along the cross-section defined in the leftmost plot. for the
NOAH-MYJ run at 15Z. Also shown are the 95% and 100% RH contours (solid lines). Wind
vectors are constructed such that if the head of one vector touches the tail of another, the horizontal windspeed is 5m/s.
Results I: sensitivity to BL scheme
Results II: sensitivity to land surface scheme
To the left is shown
vertical velocities at 1.5km
for the THERM_YSU run at 14Z.
A clear surface convergence
signal is seen: this is common to
all runs. A
Conclusions B
Although this is for a single case, the results suggest that:
The only combination of BL and LSM that produces cloud was NOAH_MYJ.
The cloud is reasonably well represented and has realistic initiation and
termination times, depth and structure;
The MYJ scheme is preferable to the YSU scheme; the latter is too vigorous in its mixing: moisture is transported away from the BL.
The NOAH land surface scheme provides the necessary surface moisture for the cloud to develop; without it, there is no cloud.
Difference plots along AB, showing q(NOAH_MYJ) - q(THERM_MYJ)
for (a) 08Z and (b) 11Z. (coloured contours, g/kg)
Difference plots of q2(NOAH_MYJ)-q2(THERM_MYJ) for (a) 13Z, (b) 14Z and (c) 15Z. Also shown are isosurfaces of cloud-water mixing ratio at a value of 0.1g/kg. The range of displayed values ranges from kg/kg (coloured deep blue) to 0.001kg/kg (coloured red).
Difference plots, showing q(NOAH_MYJ) - q(NOAH_YSU) for (a) 11Z and (b) 15Z (coloured contours, g/kg).
Also shown are the 95% and 100% RH contours for the NOAH_MYJ run, along cross-section AB defined by the
red line above.
References
[1]
[2] Wulfmeyer et al. (2008): "The convective and orographically induced precipitation study", Bulletin of the American Meteorological Society, 89, pp