TY  - JOUR
A1  - Pathiraja, Sahani  Darschika
A1  - Leeuwen, Peter Jan van
T1  - Multiplicative Non-Gaussian model error estimation in data assimilation
T2  - Journal of advances in modeling earth systems : JAMES
N2  - Model uncertainty quantification is an essential component of effective data assimilation. Model errors associated with sub-grid scale processes are often represented through stochastic parameterizations of the unresolved process. Many existing Stochastic Parameterization schemes are only applicable when knowledge of the true sub-grid scale process or full observations of the coarse scale process are available, which is typically not the case in real applications. We present a methodology for estimating the statistics of sub-grid scale processes for the more realistic case that only partial observations of the coarse scale process are available. Model error realizations are estimated over a training period by minimizing their conditional sum of squared deviations given some informative covariates (e.g., state of the system), constrained by available observations and assuming that the observation errors are smaller than the model errors. From these realizations a conditional probability distribution of additive model errors given these covariates is obtained, allowing for complex non-Gaussian error structures. Random draws from this density are then used in actual ensemble data assimilation experiments. We demonstrate the efficacy of the approach through numerical experiments with the multi-scale Lorenz 96 system using both small and large time scale separations between slow (coarse scale) and fast (fine scale) variables. The resulting error estimates and forecasts obtained with this new method are superior to those from two existing methods.
KW  - model uncertainty
KW  - non-Gaussian
KW  - data-driven
KW  - uncertainty
KW  - quantification
KW  - Lorenz 96
KW  - sub-grid scale
Y1  - 2022
UR  - https://publishup.uni-potsdam.de/frontdoor/index/index/docId/63112
SN  - 1942-2466
VL  - 14
IS  - 4
PB  - American Geophysical Union
CY  - Washington
ER  -