Bayesian History Matching applied to the calibration of a gravity wave
parameterization
Abstract
Breaking atmospheric gravity waves in the tropical stratosphere are
essential in driving the roughly two year oscillation of zonal winds in
this region known as the Quasi-Biennial Oscillation (QBO). As Global
Climate Models (GCM)s are not typically able to directly resolve the
spectrum of waves required to drive the QBO, parameterizations are
necessary. Such parameterizations often require knowledge of poorly
constrained physical parameters. In the case of the spectral gravity
parameterization used in this work, these parameters are the total
equatorial gravity wave stress and the half width of phase speed
distribution. Radiosonde observations are used to obtain the period and
amplitude of the QBO, which are compared against values obtained from a
GCM. We utilize two established calibration techniques to obtain
estimates of the range of plausible parameter values: History Matching
& Ensemble Kalman Inversion (EKI). History Matching is
found to reduce the size of the initial range of plausible parameters by
a factor of 98%, requiring only 60 model integrations.
EKI cannot natively provide any uncertainty quantification but is able
to produce a single best estimate of the calibrated values in 25
integrations. When directly comparing the approaches using the
Calibrate, Emulate, Sample method to produce a posterior estimate from
EKI, History Matching produces more compact posteriors with fewer model
integrations at lower ensemble sizes compared to EKI; however, these
differences become less apparent at higher ensemble sizes.