Andrew Williams
@andrewilwilliams.bsky.social
Postdoc at UC San Diego | physics of climate 🌤️ 🌍 | PhD Oxford | views my own | he/him
andrewilwilliams.github.io
andrewilwilliams.github.io
I submitted this paper on my final day as a postdoc at GFDL, and it's the culmination of a lot of learning and thinking. Let me know if you enjoy it :)
Just finishing my final commute home!
Just finishing my final commute home!
August 14, 2025 at 1:46 AM
I submitted this paper on my final day as a postdoc at GFDL, and it's the culmination of a lot of learning and thinking. Let me know if you enjoy it :)
Just finishing my final commute home!
Just finishing my final commute home!
The SSM also accurately emulates the response to warming! And doesn't go "out of bounds" in warm climates, like RRTMG does
August 14, 2025 at 1:46 AM
The SSM also accurately emulates the response to warming! And doesn't go "out of bounds" in warm climates, like RRTMG does
Implementing this simple radiation scheme in an aquaplanet model yields climate states which are almost indistinguishable from a full-complexity correlated-k scheme (RRTMG).
AND fixes most of the biases associated with gray radiation:)
AND fixes most of the biases associated with gray radiation:)
August 14, 2025 at 1:46 AM
Implementing this simple radiation scheme in an aquaplanet model yields climate states which are almost indistinguishable from a full-complexity correlated-k scheme (RRTMG).
AND fixes most of the biases associated with gray radiation:)
AND fixes most of the biases associated with gray radiation:)
The Simple Spectral Model (SSM) balances accuracy and clarity by using simple, analytic functions to represent H2O and CO2 spectroscopy.
You only need 10 parameters to do this, as opposed to the huge lookup tables in correlated-k schemes (10^3-10^4 parameters...)
You only need 10 parameters to do this, as opposed to the huge lookup tables in correlated-k schemes (10^3-10^4 parameters...)
August 14, 2025 at 1:46 AM
The Simple Spectral Model (SSM) balances accuracy and clarity by using simple, analytic functions to represent H2O and CO2 spectroscopy.
You only need 10 parameters to do this, as opposed to the huge lookup tables in correlated-k schemes (10^3-10^4 parameters...)
You only need 10 parameters to do this, as opposed to the huge lookup tables in correlated-k schemes (10^3-10^4 parameters...)
📢📢 New preprint alert! 📢📢
Radiation is a key piece of climate models, but comes with a trade-off: use an accurate scheme (which is difficult to understand), or a simple scheme (which is not very accurate)...
Here I introduce a scheme which bridges this gap!
arxiv.org/abs/2508.09353
Radiation is a key piece of climate models, but comes with a trade-off: use an accurate scheme (which is difficult to understand), or a simple scheme (which is not very accurate)...
Here I introduce a scheme which bridges this gap!
arxiv.org/abs/2508.09353
August 14, 2025 at 1:46 AM
📢📢 New preprint alert! 📢📢
Radiation is a key piece of climate models, but comes with a trade-off: use an accurate scheme (which is difficult to understand), or a simple scheme (which is not very accurate)...
Here I introduce a scheme which bridges this gap!
arxiv.org/abs/2508.09353
Radiation is a key piece of climate models, but comes with a trade-off: use an accurate scheme (which is difficult to understand), or a simple scheme (which is not very accurate)...
Here I introduce a scheme which bridges this gap!
arxiv.org/abs/2508.09353
Under climate change, the polar regions warm *faster* than the rest of the world ("polar amplification", PA).
But, is this always the case?
In this preprint (with Tim Merlis) we studied the 'state-dependence' of PA—feedback welcomed! :)
andrewilwilliams.github.io/papers/pa_widerange_main.pdf
But, is this always the case?
In this preprint (with Tim Merlis) we studied the 'state-dependence' of PA—feedback welcomed! :)
andrewilwilliams.github.io/papers/pa_widerange_main.pdf
July 18, 2025 at 2:47 PM
Under climate change, the polar regions warm *faster* than the rest of the world ("polar amplification", PA).
But, is this always the case?
In this preprint (with Tim Merlis) we studied the 'state-dependence' of PA—feedback welcomed! :)
andrewilwilliams.github.io/papers/pa_widerange_main.pdf
But, is this always the case?
In this preprint (with Tim Merlis) we studied the 'state-dependence' of PA—feedback welcomed! :)
andrewilwilliams.github.io/papers/pa_widerange_main.pdf
Can confirm they've hit NYC
July 14, 2025 at 10:32 PM
Can confirm they've hit NYC
When Earth warms, the total rainfall increases.
Here we show that this change in rainfall is also sensitive to the *pattern* of warming, build a theory to explain why, and use it to explain why rainfall increases more in uniform warming exps than abrupt-4xCO2 :)
essopenarchive.org/doi/full/10....
Here we show that this change in rainfall is also sensitive to the *pattern* of warming, build a theory to explain why, and use it to explain why rainfall increases more in uniform warming exps than abrupt-4xCO2 :)
essopenarchive.org/doi/full/10....
July 6, 2025 at 12:58 PM
When Earth warms, the total rainfall increases.
Here we show that this change in rainfall is also sensitive to the *pattern* of warming, build a theory to explain why, and use it to explain why rainfall increases more in uniform warming exps than abrupt-4xCO2 :)
essopenarchive.org/doi/full/10....
Here we show that this change in rainfall is also sensitive to the *pattern* of warming, build a theory to explain why, and use it to explain why rainfall increases more in uniform warming exps than abrupt-4xCO2 :)
essopenarchive.org/doi/full/10....
Sky's the limit, folks!
Keep calling your reps and tell them to #SaveOurForecasts ❤️
wclivestream.com/act
Let's hit 10k!
Keep calling your reps and tell them to #SaveOurForecasts ❤️
wclivestream.com/act
Let's hit 10k!
June 3, 2025 at 9:21 PM
Sky's the limit, folks!
Keep calling your reps and tell them to #SaveOurForecasts ❤️
wclivestream.com/act
Let's hit 10k!
Keep calling your reps and tell them to #SaveOurForecasts ❤️
wclivestream.com/act
Let's hit 10k!
7765 calls made so far! But we still have so much work to do...
Keep calling your reps and telling them to #SaveOurForecasts !
wclivestream.com/act
Keep calling your reps and telling them to #SaveOurForecasts !
wclivestream.com/act
June 2, 2025 at 2:34 PM
7765 calls made so far! But we still have so much work to do...
Keep calling your reps and telling them to #SaveOurForecasts !
wclivestream.com/act
Keep calling your reps and telling them to #SaveOurForecasts !
wclivestream.com/act
We can link this weakening of mass fluxes along isotherms (left) to changes in the tropical lapse rate (right), and a moist adiabat is able to capture this (orange line, theory).
:))))
:))))
April 28, 2025 at 1:17 PM
We can link this weakening of mass fluxes along isotherms (left) to changes in the tropical lapse rate (right), and a moist adiabat is able to capture this (orange line, theory).
:))))
:))))
The key insight of this theory is to look at changes in convective mass flux with warming, *along isotherms*!
When viewed in this coordinate system, a variety of models (CRMs, GCMs, GSRMs) simulate a robust, 3-5%/K weakening of mass fluxes with surface warming.
When viewed in this coordinate system, a variety of models (CRMs, GCMs, GSRMs) simulate a robust, 3-5%/K weakening of mass fluxes with surface warming.
April 28, 2025 at 1:16 PM
The key insight of this theory is to look at changes in convective mass flux with warming, *along isotherms*!
When viewed in this coordinate system, a variety of models (CRMs, GCMs, GSRMs) simulate a robust, 3-5%/K weakening of mass fluxes with surface warming.
When viewed in this coordinate system, a variety of models (CRMs, GCMs, GSRMs) simulate a robust, 3-5%/K weakening of mass fluxes with surface warming.
But it's not all bad news! We show that changes in convective mass fluxes CAN be predicted using simple physical theory and knowledge of the control profile of mass flux :)
More details in the paper!
More details in the paper!
April 28, 2025 at 1:12 PM
But it's not all bad news! We show that changes in convective mass fluxes CAN be predicted using simple physical theory and knowledge of the control profile of mass flux :)
More details in the paper!
More details in the paper!
Furthermore, the original "verification" of P=Mq by Held & Soden was coincidental and doesn't hold up across models.
TLDR; P=Mq is dead, stop citing it.
TLDR; P=Mq is dead, stop citing it.
April 28, 2025 at 1:09 PM
Furthermore, the original "verification" of P=Mq by Held & Soden was coincidental and doesn't hold up across models.
TLDR; P=Mq is dead, stop citing it.
TLDR; P=Mq is dead, stop citing it.
A big result of our paper is also that the canonical Held & Soden (2006) scaling does not correctly predict mass flux changes (it even gets the sign wrong sometimes!)
April 28, 2025 at 1:07 PM
A big result of our paper is also that the canonical Held & Soden (2006) scaling does not correctly predict mass flux changes (it even gets the sign wrong sometimes!)
And yes, this is the same "Cleo Haussler-Williams" I acknowledge in my papers.
April 21, 2025 at 11:42 PM
And yes, this is the same "Cleo Haussler-Williams" I acknowledge in my papers.
Cleo supports NOAA-GFDL...
...be like Cleo!
...be like Cleo!
April 21, 2025 at 11:38 PM
Cleo supports NOAA-GFDL...
...be like Cleo!
...be like Cleo!
She's working hard
April 17, 2025 at 6:47 PM
She's working hard
I bought a sack which used to hold coffee beans, and my cat loves it
March 22, 2025 at 2:51 AM
I bought a sack which used to hold coffee beans, and my cat loves it
Spotted on subway
March 13, 2025 at 12:42 PM
Spotted on subway
Spotted in Princeton #2
March 12, 2025 at 2:26 PM
Spotted in Princeton #2
No one told her it was daylight savings 😭
March 9, 2025 at 1:56 PM
No one told her it was daylight savings 😭
Spotted in Princeton
March 6, 2025 at 7:25 PM
Spotted in Princeton
Patterns in tea
February 22, 2025 at 11:22 PM
Patterns in tea