Category Archives: Atmospheric Models

What is Super-Parameterization?

Super-parameterization is a type of multi-model framework (MMF), which is a technique for modeling a physical system with a wide range of important scales (such as the climate system). A model is typically designed to simulate things on a certain scale of interest, but it also needs information about things happening on smaller and larger scales. This missing information is condensed into model parameters, which can be fixed or variable. A parameterization* is a method for estimating parameter values without explicitly simulating the processes directly. Parameterizations can sometimes be thought of as very low order models. Super-parameterization replaces one or more parameterizations with a second model that is designed to simulate the processes explicitly, in order to provide more accurate parameter values back to the main “host” model. Continue reading

CESM: Apparent Errors from shr_sys_flush()

I’ve been struggling with a model error for over a week now, and it all seemed to revolve around this Fortran subroutine “shr_sys_flush()”. The error usually showed up in the log file as a “floating point exception”, but other times I got a “segmentation fault”. I had an epiphany this afternoon that will hopefully help other people with similar errors. Continue reading

Convective Parameterization Reading list

At a recent conference I was talking to a colleague about research ideas, and we kept coming back to the conclusion that we don’t know as much as we should about how clouds are treated in the various models used around the world. There are many different schemes in use today and most of them are closely related to one another, but it’s hard to keep track of the subtle differences between the approaches. Sometimes it’s hard to find any information about the particular configuration of the convective schemes in certain models. I decided to compile a list of the different types of parameterization schemes, and gather some notes on the key papers that developed these schemes. Continue reading

CESM: Adding an Idealized Land Mass to an Aqua-Planet

While working on my current research on the African monsoon system, I often wonder about how the monsoon would change if I could reshape the african continent. But to answer this, it would be nice if you could simplify the problem and remove all the other continents. I’ve talked to other people who have similar question about how the Inter-Tropical Convergence Zone (ITCZ) is affected by the existence of land masses. Below are some notes for setting up a model simulation using the NCAR CESM with an idealized land mass for exploring these questions. Continue reading

CESM: Aqua-Planet with a Slab Ocean Model (SOM)

In a previous post I outlined how I set up CESM in aqua-planet mode with a specified sea surface temperature (SST) distribution. However, there are a few drawbacks to using prescribed SST. The biggest caveat is that fixed surface temperature can effectively be an infinite source of energy. I saw a poster a at a meeting last year that compared a simulation with prescribed SST to another with a slab ocean model (SOM)  and the results were very striking, so I started thinking that I need to explore this type of modelling more. Below are my notes for setting up a aqua-planet slab-ocean configuration in CESM 1.2 on the Yellowstone machine (Linux) with the intel compiler.

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CESM: Common Errors when Building CESM 1.2 (OSX)

In a previous post, I exhaustively outlined the process of setting up the CESM model version 1.2 to run in single column mode on a Mac running OSX 10.9.5 (i.e. Darwin) with GCC 4.9.2.

This post documents some errors I ran into along the way. If I find more in the future, I’ll probably make a new post instead of updating this one, so be sure to check for new posts here, if you are looking for solutions to CESM bugs. Continue reading

CESM: A [more] Portable Climate Model for Single-Column Experiments

Some years ago I did a small project that involved running the NCAR Community Earth System Model (CESM) in a series of single-column model (SCM) experiments to test some ideas about the diurnal cycle of convection (or diel cycle). One of my graduate school professors, Dave Randall, has a nice explanation of single-column models, Continue reading