the simulation of a deep convective cloud in complex orography: the 15 july 2007 case from cops
DESCRIPTION
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 : [email protected]. - PowerPoint PPT PresentationTRANSCRIPT
The simulation of a deep convective cloud in complex orography: the 15 July 2007 case from COPSRalph Burton, Alan Gadian, Alan Blyth, Stephen Mobbs National Centre for Atmospheric Science, University of Leeds, UK contact:
Run name
BL scheme Land surface
Comments
THERM_YSU
YSU Thermal diffusion
Very shallow, very isolated cloud.
THERM_MYJ
MYJ Thermal diffusion
Very shallow cloud.
NOAH_YSU
YSU NOAH LSM
Very shallow cloud.
NOAH_MYJ
MYJ NOAH LSM
Deep cloud extending to approx 12km in altitude.
Numerical and dynamical parameters
Nest number1 2
Grid sizes and resolution
550x550 x 50 vertical levels, 3.6km
301x241 x 50 vertical levels, 1.2km
Time step 18s 6sCumulus parametrisation
None None
Microphysics Morrison MorrisonRadiation (SW) Dudhia DudhiaRadiation (LW) RRTM RRTM
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 -0.001kg/kg (coloured deep blue) to 0.001kg/kg (coloured red).
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.
COPSConvective and orographically-induced
precipitation study
Location of the COPS field phase. Map taken from the COPS brochure [1]. For an overview of the COPS campaign see [2].
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,www.cops2007.de
WRF modelling: sensitivity to boundary-layer and land-surface schemes
Domains used in the WRF simulation. The outer domain is at 6.1km resolution; the inner domain at 2.1km resolution.
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.
Table I Table II
Results I: sensitivity to BL scheme
To the left is shownvertical velocities at 1.5kmfor the THERM_YSU run at 14Z.A clear surface convergencesignal is seen: this is common toall runs.
Results II: sensitivity to land surface scheme
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 thered line above.
Conclusions
All runs initialised at 0Z 15th July with GFS analyses
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.
References
[1] http://www.cops2007.de/pics/COPS_TRACKS_english.pdf, http://www.cops2007.de/pics/COPS_TRACKS_deutsch.pdf[2] Wulfmeyer et al. (2008): "The convective and orographically induced precipitation study", Bulletin of the American Meteorological Society, 89, pp1477-1486
A
B