Applied & Computational Mathematics seminar: Predicting the Weather, 4d-Var, Hybrid Tangent Linear Models, A.I. and JEDI

Speaker:  Christian Sampson, Joint Center for Satellite Data Assimilation

Title:  Predicting the Weather, 4d-Var, Hybrid Tangent Linear Models, A.I. and JEDI

Abstract:  Weather modeling in conjunction with Data Assimilation (DA) has proven to provide effective weather forecasts that can both help you plan your day to save your life. We often refer to the combination of weather models and DA as Numerical Weather Prediction (NWP). One of the most widely employed DA methods in NWP is a variational method called 4d-Var. In this method, a cost function involving the model background error and a series of observations over time is minimized to find the best initial condition from which to run your model so that model forecast is consistent with observations. 4d-Var has been shown to provide the most reliable weather forecasts to date, but is not without its pitfalls. In particular, 4d-Var depends heavily on a tangent linear model (TLM) and an adjoint to the tangent linear model. While conceptually simple, coding these two elements is extremely time intensive and difficult. A small change in the larger weather model can induce months of work on its TLM and adjoint delaying the benefits of improvements on the model side. In this talk I will introduce the 4d-var method in general and present work on a Hybrid Tangent Linear Model (HTLM) developed in [Payne 2021] which is aimed at improving TLMs as well as allowing the use of incomplete TLMs when model physics changes. I will give a brief overview of how methods in machine learning could be useful in DA and also touch on the Joint Effort for Data Integration (JEDI) project which now includes an HTLM and how you can use JEDI for DA or contribute your own code.

Time:  Friday, November 3, 2023 - 10:00am-11:00am

Place:  Exploratory Hall, Room 4106