Summer Plan 2010. Estatio Gutierrez. June. WAS*IS workshop: Reading papers. Preparing a 30-min presentation. Selection of urban heat island cases from weatherbug data (summer 2008) and NYCMetNet data (summer 2009).
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Horizontal advection orders for momentum: 5th (available: 2th, 6th)
Vertical advection orders for momentum: 3th (available: 2th, 5th)
moist_adv_opt and scalar_adv_opt: positive-definite advection option (monotonic option is also available)
This are a few notes that I found about both advection schemes. I was already using all the options that they recommend:
The positive-definite and monotonic options are available for moisture, scalars, chemical scalers and TKE in the ARW solver. Both the monotonic and positive-definite transport options conserve scalar mass locally and globally and are consistent with the ARW mass conservation equation. We recommend using the positive-definite option for moisture variables on all real-data simulations. The monotonic option may be beneficial in chemistry applications and for moisture and scalars in some instances.
When using these options there are certain aspects of the ARW integration scheme that should be considered in the simulation configuration.
(1) The integration sequence in ARW changes when the positive-definite or monotonic options are used. When the options are not activated, the timestep tendencies from the physics (excluding microphysics) are used to update the scalar mixing ratio at the same time as the transport (advection), and the microphysics is computed and moisture is updated based on the transport+physics update. When the monotonic or positive definite options are activated, the scalar mixing ratio is first updated with the physics tendency, and the new updated values are used as the starting values for the transport scheme. The microphysics update occurs after the transport update using these latest values as its starting point. It is important to remember that for any scalars, the local and global conservation properties, positive definiteness and monotonicity depend upon each update possessing these properties.
(2) Some model filters may not be positive definite.
i. diff_6th_opt = 1 is not positive definite nor monotonic. Use diff_6th_opt = 2 if you need this diffusion option (diff_6th_opt = 2 is monotonic and positive-definite). We have encountered cases where the departures from monotonicity and positive-definiteness have been very noticeable.
ii. diff_opt = 1 and km_opt = 4 (a commonly-used real-data case mixing option) is not guaranteed to be positive-definite nor monotonic due to the variable eddy diffusivity K. We have not observed significant departures from positive-definiteness or monotonicity when this filter is used with these transport options.
iii. The diffusion option that uses a user-specified constant eddy viscosity is positive definite and monotonic.
iv. Other filter options that use variable eddy viscosity are not positive definite or monotonic.
(3) Most of the model physics are not monotonic nor should they be - they represent sources and sinks in the system. All should be positive definite, although we have not examined and tested all options for this property.
(4) The monotonic option adds significant smoothing to the transport in regions where it is active. You may want to consider turning off the other model filters for variables using monotonic transport (filters such as the second and sixth order horizontal filters). At present it is not possible to turn off the filters for the scalars but not for the dynamics using the namelist - one must manually comment out the calls in the solver. In the next release we will make this capability available through the namelist.