Sensitivity of a long-range numerical weather forecast model to small changes of model parameters

M B Gavrilov,Z Janjić,G R Jovanović

doi:10.5194/asr-6-13-2011

Abstract

Abstract. Sensitivity of extended-range numerical weather forecasts to small changes of model parameters is studied for two cases. In the first case the Earth radius was perturbed. In the other case changes of the gravity were introduced. The results for the 500 hPa geopotential fields are presented on hemispheric maps and intercompared visually and using RMS differences of the perturbed and reference forecasts. During about the first 10 days of integration the results indicate modest sensitivity of the forecasts to the parameter variation. After this period the forecasts diverge rapidly and start to differ significantly. Repeated integrations on the same computer using the same model setup and the same initial conditions yield identical results.

Highlights

Predictability of the atmosphere and accuracy of atmospheric models are still among the central issues of meteorology and atmospheric modeling. Thompson (1957) was among the first to investigate the limits of predictability of the barotropic and baroclinic atmospheres. Lorenz (1969a, b, 1973) continued and expanded this research
Sensitivity of extended-range numerical weather forecasts to small changes of model parameters is studied for two cases
The sensitivity tests of numerical integrations to small changes in initial conditions in the works of Lorenz (1963, 1965) were important for testing the accuracy and predictability of atmospheric models, and led to the discovery of a new phenomenon in nonlinear systems known as deterministic chaos

Summary

Introduction

Predictability of the atmosphere and accuracy of atmospheric models are still among the central issues of meteorology and atmospheric modeling. Thompson (1957) was among the first to investigate the limits of predictability of the barotropic and baroclinic atmospheres. Lorenz (1969a, b, 1973) continued and expanded this research. Lorenz (1969a, b, 1973) continued and expanded this research. These investigations showed that the limit of predictability for an atmospheric model was about 12 days. The sensitivity tests of numerical integrations to small changes in initial conditions in the works of Lorenz (1963, 1965) were important for testing the accuracy and predictability of atmospheric models, and led to the discovery of a new phenomenon in nonlinear systems known as deterministic chaos. We keep the initial conditions unchanged, and instead vary within the respective limits of their natural variability two model parameters that are commonly assumed to be constant. By doing so we wanted to demonstrate that the growth of differences between the so-

The model

Experiment setup

Results