Idealized Tropical Cyclone's SST

[prabeshkshetri]

Hello,
I ran some cases with the Idealized TC with various values of SST (by modifying the 'module_initialize_tropical_cyclone.F'). The values of 10m max windspeed tend to converge after 15 days. I wanted to know the effects of changing sea surface temperature on TC. Are the values I modified just for the initial vortex or are these SST are for the bottom boundary condition for the entire simulation period? I wanted to know the forcings that sustains the cyclone and where I could modify them. I have modified the variables for the initial vortex in the mentioned file. Are there other places in the code I could further modify. I would be grateful for help with this. I have attached the plot of surface max windspeed.

 

[kwerner]

Hi,
Apologies for the delay in response. If you're still experiencing problems, will you attach the file you modified, as well as the namelist.input file you're using so that I can take a look? Please also let me know which version of WRF you are running. Thanks!

 

[prabeshkshetri]

Hello kwerner,
Thank you for your reply. I have attached the file where I modified the SST for idealized tropical cyclone. It is in the folder ../WRF-4.2.2/dyn_em of the program. The modification is in the line 171 and, is as following


!-----------------------------------------------------------------------


! USER SETTINGS
! Parameters for analytic vortex:
! Reference: Rotunno and Emanuel, 1987, JAS, p. 549

r0 = 412500.0 ! outer radius (m)


rmax = 82500.0 ! approximate radius of max winds (m)


vmax = 15.0 ! approximate value of max wind speed (m/s)


zdd = 20000.0 ! depth of vortex (m)


! other settings:


fcor = 5.0e-5 ! Coriolis parameter (1/s)

sst = 30.0 ! sea-surface temperature (Celsius) !!!!! MODIFIED from 28 to 30


!-----------------------------------------------------------------------


I compiled the idealized case after modification and ran those simulations. Even if they are idealized cases, the intensity do not seem to sustain especially for the higher sst cases. The sst28 (default case) and sst26 only seem to sustain their intensity. I found a paper where similar cases were run and they mentioned about introduction of a relaxation term 'to counter the stabilizing effect of the convection'. Also those cases were run shorter duration (about 6 days). One of the paper authors is from NCAR. The paper link is as following.

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020MS002057

Maybe the tropical cyclone gets affected by heat flux or momentum flux from the increased sst so there is a disturbance in reaching a steady state condition. Could you please look into this, thanks

 

[kwerner]

Thanks for sending that. Can you please also attach the namelist.input file you're using?

 

[prabeshkshetri]

Please find the attached namelist.input file I used for the simulation?

 

[kwerner]

Thanks for sending those. I spoke to the author of the publication you shared and they said they think you need to modify the initial sounding by the same temperature, and the moisture by 7% per degree. You have the relaxation term already active.