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.

 

[Qingyang Xiong]

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.

Hello, I would like to ask specifically how to modify the sounding, because I found that input_sounding seems to be a profile. Should I only modify the temperature and humidity at the sea level layer?

 

[kwerner]

Hello, I would like to ask specifically how to modify the sounding, because I found that input_sounding seems to be a profile. Should I only modify the temperature and humidity at the sea level layer?

The input_sounding file is a text file, so if you want to modify the temperature and humidity, you probably need to modify it so that it makes sense at all levels. The file won't change based on a modification to the surface level.

 

[Qingyang Xiong]

The input_sounding file is a text file, so if you want to modify the temperature and humidity, you probably need to modify it so that it makes sense at all levels. The file won't change based on a modification to the surface level.

Thank you for your reply. I hope to confirm whether I made the appropriate changes. In the original code, the temperature is 28°C, and now I want to test the situation with an SST of 29°C. So I have increased the temperature in each row of the second column in the input_sounding by 1°C, and increased the relative humidity in each row of the third column by 7% based on the original values. Is that correct?

 

[Qingyang Xiong]

I found the reference for the Jordan 1958 sounding, and it appears that the second column of input_sounding might be the potential temperature, while the third column is specific humidity. This makes me more confused. First, the potential temperature at the surface in the sounding is 298K, corresponding to 25°C, which is inconsistent with the 28°C SST in the code (module_initialize_tropical_cyclone.F). Should I make adjustments based on one of these values? Second, regarding the temperature increase by 1°C corresponding to a 7% increase in humidity, could you please clarify whether this refers to relative humidity (f), and if so, do I need to manually convert it to specific humidity?

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.

 

[Qingyang Xiong]

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.View attachment 10975

Hello, have you solved the problem?

 

[kwerner]

Many apologies for the delay. I've been out of the office for the past week and 1/2. Yes, it does look like you're interpreting the literature correctly and that the input_sounding file provides (2nd column) potential temp and (3rd column) specific humidity

I believe the differences you're seeing are related to the air temperature at the surface, or at pressure level 1015.10 (~26 C; potential temp = 298.1718), versus the sea surface temperature for the sounding location (~28 C).

 

[Qingyang Xiong]

Many apologies for the delay. I've been out of the office for the past week and 1/2. Yes, it does look like you're interpreting the literature correctly and that the input_sounding file provides (2nd column) potential temp and (3rd column) specific humidity

I believe the differences you're seeing are related to the air temperature at the surface, or at pressure level 1015.10 (~26 C; potential temp = 298.1718), versus the sea surface temperature for the sounding location (~28 C).

Thank you for your further response. I would like to know how to specifically "modify the initial sounding by the same temperature, and the moisture by 7% per degree." For example, if I want to simulate an SST of 29°C, should I increase the temperature by 1°C at every level from the original sounding and then calculate the corresponding potential temperature and moisture?

Additionally, if a 1°C increase in temperature corresponds to a 7% increase in moisture, it seems that the humidity in the lower levels reaches 100% when the SST exceeds 30°C. Is this reasonable? Moreover, is there any theoretical basis for making such modifications?

Thank you!

My calculation code is as follows for your reference.

 

[kwerner]

Thank you for your further response. I would like to know how to specifically "modify the initial sounding by the same temperature, and the moisture by 7% per degree." For example, if I want to simulate an SST of 29°C, should I increase the temperature by 1°C at every level from the original sounding and then calculate the corresponding potential temperature and moisture?

Yes, I believe that is what you will need to do.

Additionally, if a 1°C increase in temperature corresponds to a 7% increase in moisture, it seems that the humidity in the lower levels reaches 100% when the SST exceeds 30°C. Is this reasonable?

Yes, that probably is reasonable. If the air temperature in that area is higher, increasing humidity and instability, it's possible it's actually raining in the area.

Moreover, is there any theoretical basis for making such modifications?

I'm not certain of where this information would be documented, unless it's in the reference the other user mentioned above.