Author Archives: Walter

de Roode et al. (2012): Parameterization of the Vertical Velocity Equation for Shallow Cumulus Clouds

I’ve been stewing on an idea to build a convective parameterization for a couple years, but there are a lot of issues to work out so I’ve been trying to study up on how other parameterizations work. The biggest issue with a convective parameterization always seems to revolve around entrainment. In reading about recent parameterization developments, like Chikira and Sugiyama (2010), many people seem to like the idea of relating entrainment to the vertical velocity of the cloud updraft. This is not a new idea, but it has taken awhile to be utilized in weather and climate models. The paper discussed below provides a great discussion of this relationship, and I was surprised to learn that it is based on an inaccurate assumption about how important entrainment is for cloud momentum.

de Roode, S.R., A.P. Siebesma, H.J. Jonker, and Y. de Voogd, 2012: Parameterization of the Vertical Velocity Equation for Shallow Cumulus Clouds. Mon. Wea. Rev., 140, 2424–2436.

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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

House Committee Hearing on Climate Science (March 29, 2017)

This morning I listened to the recent hearing on climate science for the house of representatives committee on science, space, and technology. I found the exchange very fascinating. I was disappointed to hear the naive questions coming from the representatives. Some are still touting the myth of the cooling predictions in the 70’s.  Another congressman seemed to be on a witch hunt by aggressively asking a panel witness to prove that he wasn’t part of the union of concerned scientists. Aside from the conduct of the representatives, I wanted to share some thoughts about the conduct of the panel.  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

Understanding Earth System Sensitivity (ESS)

In spite of considering myself a “climate expert” I still struggle a bit with understanding how climate sensitivity is estimated. Admittedly, part of my confusion is because the climate system has multiple definitions of sensitivity depending on the timescale of interest. That’s why a thought experiment from a recent article caught my eye. The post was written by Gavin Schmidt and describes why the earth system sensitivity (ESS) cannot be estimated by regressing temperature and radiative forcing estimates across ice-age cycles. Continue reading

Moving to Lawrence-Livermore National Lab

This is just a personal update. I’m wrapping up my work on African easterly waves at NC State and heading out to California to start a new job at Lawrence-Livermore National Lab (LLNL). I’ll be working on a relatively new climate model called ACME for the US Department of Energy. I’m not sure how the recent political environment will affect the funding for climate work at National labs. There seems to be sufficient evidence to be concerned, but I’m not too worried at the moment. Continue reading

A Comparison of Methods for Estimating Diabatic Heating

Understanding the various sources of heating in the atmosphere, like convection and radiation,  is critically important in Tropical meteorology. Unfortunately we cannot just go out and directly measure the temperature tendency from convection. However, we can measure the temperature and estimate how it changes as a result of air flowing over an area, and then calculate the “leftover” residual temperature tendency to get an idea of how diabatic processes (i.e. convection and radiation) are heating the atmosphere. In practice, there are two widely used approaches to produce these estimates, and the goal of this article is to provide a brief comparison of them. Continue reading