em_hill2d_x: Gradual start up

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dkingsmill
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Joined: Thu Jul 23, 2020 10:30 pm

em_hill2d_x: Gradual start up

Post by dkingsmill » Thu Jul 23, 2020 10:41 pm

I have been working with the em_hill2d_x idealized case. By default, the simulation starts with the cross-ridge wind speed specified in the input sounding. I would like to modify the code so that the wind increases gradually, reaching its input-sounding value at some point after initialization. Can you provide guidance on the sections of code that need to be modified to implement this feature? Thanks.

Ming Chen
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Joined: Mon Apr 23, 2018 9:42 pm

Re: em_hill2d_x: Gradual start up

Post by Ming Chen » Thu Jul 30, 2020 5:15 pm

HI,
I take a quick look at the codes and below is just my preliminary idea.
(1) Please look at the code module_initialize_ideal, which reads input_sounding for ideal cases. You may either change the input, or modify this code to change the initial value of U
(2) module_bc_em.F processes all types of boundary. You need to look at the part for periodic lateral boundary, and probably add an extra tendency term to the variables you want to change.
Hope this is helpful.
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dkingsmill
Posts: 2
Joined: Thu Jul 23, 2020 10:30 pm

Re: em_hill2d_x: Gradual start up

Post by dkingsmill » Thu Jul 30, 2020 9:48 pm

Hi,
Thanks for your response. I figured that the module_initialize_ideal.F code would need to get modified in order to achieve the desired result. Specifically, I would need to override the U from the input sounding and set it to zero (or something very small). However, I am confused about your suggestion about modifying module_bc_em.F. My (possibly incorrect) conception about what needs to be done has more to do with the base state than boundary conditions. It is my understanding that the base state for this idealized case remains unchanged over time by default. I would simply like to increase the base state U from zero (or near zero) to the value specified in the input sounding over a period time after initialization. I want to increase the base state U over the entire domain, not just at the boundaries. With this in mind, I am thinking that code in solve_em.F will have to be modified (in addition to that in module_initialize_ideal.F). Among other things, solve_em.F keeps track of the time since model initialization, which would allow a specification of a new base state U at each time step (e.g., increasing base state U from 0 to 10 m/s over 30 minutes of simulation time and then keeping the base state U at 10 m/s for the remainder of the simulation). I see the grid%u_base variable in solve_em.F; it seems to be used in a call to the rk_tendency subroutine. Is the logic correct? If not, can you clarify?

My thinking is based on what I have read in another help topic dealing with releasing a warm bubble well after initialization of the idealized supercell case (https://forum.mmm.ucar.edu/phpBB3/viewt ... =472#p2400). While this is a bit different from what I desire, there is the common element of changing something that is typically done at initialization. kwerner suggested changes to module_initialize_ideal.F and solve_em.F to accomplish the desired outcome of delaying bubble release. Would this approach also work for gradually increasing the base state U after initialization?

Thanks again for your assistance.

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