Big upgrade to GFS for next October

[cycloneye]

Big upgrade to GFS for next October.

https://www.weather.gov/media/notificat ... GFSv17.pdf

[USTropics]

This is a MAJOR upgrade to the GFS model actually. I'll outline below everything that is being changed.

Main Takeaway
The core change is transitioning the GFS into a fully coupled Earth-system model. This means instead of just looking at the atmosphere, the new model will tightly link the atmosphere, land, ocean, sea ice, and ocean wave model components together to improve overall global weather prediction.

Other big improvements include:

• Higher Resolution: horizontal resolution is being increased from 13km to 9km. This allows the model to explicitly resolve much finer structural features. For tropical cyclones, this means a sharper representation of the eyewall, stronger convective towers, and a more defined radius of maximum winds, tightening the error bounds on intensity forecasts.
• New Ocean and Ice Models: Replacement of these models with Modular Ocean Model (MOM6) for oceans and the Community Ice CodE (CICE6) for sea ice.
• Upgraded Wave Model: WAVEWATCH III will still be utilized, but now has an unstructured grid and can exchange feedback directly with the atmosphere and ocean instead of needing to be parameterized.
• New Convective Scheme: One of my favorite changes, the upgrade will now use the Thomspon-Eidhammer convective scheme for cloud formation and precipitation.
• Hurricane Intensity Enhancements: The new convective scheme leads into the model introducing a new parameterization for environmental wind shear. It also features revised interactions between the planetary boundary layer and convection, which are explicitly aimed at improving hurricane intensity forecasts.
• Surface Fluxes and Sea Spray: This one is also very exciting for me (one of the aspects of my PhD work right now in identifying RI precursors), a new sea spray parameterization is being implemented. By implementing a dedicated sea spray parameterization alongside momentum and thermal roughness, this update fundamentally alters how enthalpy fluxes are calculated at the air-sea interface.
  
  At extreme wind speeds, sea spray acts as a massive latent heat source while simultaneously modifying the aerodynamic roughness of the ocean surface. This directly impacts hurricane boundary layer inflow thermodynamics, which is the primary engine driving rapid intensification. By accurately modeling this spray, GFSv17 can better represent the energetic triggers that cause a storm to rapidly bomb out
• MJO Prediction: The upgrade includes a new prognostic convective updraft fraction parameterization. This specific addition improves the prediction of the Madden-Julian Oscillation (MJO), which is a major driver of tropical weather patterns and hurricane genesis

[TeamPlayersBlue]

At extreme wind speeds, sea spray acts as a massive latent heat source while simultaneously modifying the aerodynamic roughness of the ocean surface. This directly impacts hurricane boundary layer inflow thermodynamics, which is the primary engine driving rapid intensification. By accurately modeling this spray, GFSv17 can better represent the energetic triggers that cause a storm to rapidly bomb out

Never thought of this but this is a huge factor for sure in RI.

[Nimbus]

Hurricane boundary layer rolls have been observed in four hurricanes during landfall.
Ideal heat transfer situation that would signal rapid intensification.
Are there new satellites that could detect boundary layer dynamics?

[USTropics]

Hurricane boundary layer rolls have been observed in four hurricanes during landfall.
Ideal heat transfer situation that would signal rapid intensification.
Are there new satellites that could detect boundary layer dynamics?

Yes and no. Satellites unfortunately cannot fully do this because we need to be able to determine vertical wind profiles (and satellites can't do this in heavily convective regimes). My work is specifically looking at high resolution nested WRF data for Ian, Michael, Harvey, and Idalia (we look at three separate models here to determine flux contributions: the uncoupled, coupled with ocean, and sea-spray WRF model outputs).

In order to do this, we have to determine the inflow boundary layer to separate out enthalpy fluxes inflowing into the center of a cyclone vs. fluxes that are being transported away in the outflow layer. This can be calculated at each timestep based on the radial wind profile (where a sign change determines the inflow layer vs. outflow layer). Here is a snapshot of the webapp I'm building out showing this:



With that said, another student I am working with is doing their MS thesis on in-situ data to verify what we are finding in the models. This is using a combination of tail doppler radar, dropsondes, scatterometer, and unflagged polar orbiting satellite data.

[Nimbus]

Hurricane boundary layer rolls have been observed in four hurricanes during landfall.
Ideal heat transfer situation that would signal rapid intensification.
Are there new satellites that could detect boundary layer dynamics?

Yes and no. Satellites unfortunately cannot fully do this because we need to be able to determine vertical wind profiles (and satellites can't do this in heavily convective regimes). My work is specifically looking at high resolution nested WRF data for Ian, Michael, Harvey, and Idalia (we look at three separate models here to determine flux contributions: the uncoupled, coupled with ocean, and sea-spray WRF model outputs).

In order to do this, we have to determine the inflow boundary layer to separate out enthalpy fluxes inflowing into the center of a cyclone vs. fluxes that are being transported away in the outflow layer. This can be calculated at each timestep based on the radial wind profile (where a sign change determines the inflow layer vs. outflow layer). Here is a snapshot of the webapp I'm building out showing this:

https://i.imgur.com/fH9X6qx.png

With that said, another student I am working with is doing their MS thesis on in-situ data to verify what we are finding in the models. This is using a combination of tail doppler radar, dropsondes, scatterometer, and unflagged polar orbiting satellite data.

I found a few papers describing the boundary roll phenomena that used land based Doppler radar imagery in combination with early satellite SAR. Friction from rough seas produce the phenomena so if you can find neatly distributed rolls then you know there are rough seas with optimum heat transfer from sea spray.

https://www.researchgate.net/figure/Sch ... _237476136

Several new SAR equipped satellites launched recently for the Copernicus Sentinel 1 program.

These have an onboard AIS system for detecting boundary layer phenomena that can see through a denser column of contamination. Since they had 20 years to improve equipment to find these boundary layer rolls in hurricanes they might at least detect them with an oblique scan down through the eye of an active hurricane where the rolls have their smallest diameter.

https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-1/Sentinel-1D_delivers_first_images_from_Antarctica_to_Bremen