Ensemble Forecasting Experiments Using the Breeding of Growing Modes with Perturbed Land Variables

Xin-Min Zeng,Yong-Jing Liang,Yan Wang ,Yuxi Zheng

doi:10.3390/atmos12121578

Abstract

Although land surface influences atmospheric processes significantly, insufficient studies have been conducted on the ensemble forecasts using the breeding of growing modes (BGM) with perturbed land surface variables. To investigate the practicability of perturbed land variables for ensemble forecasting, we used the ARWv3 mesoscale model to generate ensembles for an event of 24 h heavy rainfall with perturbed atmospheric and land variables by the BGM method. Results show that both atmospheric and land variables can generate initial perturbations with BGM, except that they differ in time and saturation characteristics, e.g., saturation is generally achieved in approximately 30 h with a growth rate of ~1.30 for atmospheric variables versus 102 h and growth rate of 1.02 for land variables. With the increase in precipitation, the importance of the perturbations of land variables also increases as compared to those of atmospheric variables. Moreover, the influence of the perturbations of land variables on simulated precipitation is still relatively large, although smaller than that of atmospheric variables, e.g., the spreads of perturbed atmospheric and land subsets were 7.3 and 3.8 mm, respectively. The benefits of perturbed initialisation can also be observed in terms of probability forecast. All findings indicate that the BGM method with perturbed land variables has the potential to ensemble forecasts for precipitation.

Highlights

As discussed by Keil et al [31], soil moisture heterogeneity appears to have the greatest influence on convection during weak synoptic forcing, which implies that our case study during strong synoptic forcing in the early summer is unlikely to overestimate the impact of soil moisture perturbation
This study aimed to investigate whether slowly evolving land surface variables are The results of this study are consistent with those obtained by Wang et al [30], both suitable for generating the initial perturbations for ensemble forecasts using the breeding of growing modes (BGM)
Theensemble initial perturbations of notewor‐. These thy that, as discussed by Keil et al [31], soil moisture heterogeneity appears to have the greatest influence on convection during weak synoptic forcing, which implies that our case study during strong synoptic forcing in the early summer is unlikely to overestimate the impact of soil moisture perturbation

Summary

Introduction

One of the pioneering works of Lorenz [1] indicated the limit of deterministic prediction induced by the chaotic nature of the atmosphere; it was noted that this limit for the wintertime atmosphere was approximately two weeks, as determined from numerical studies of the general circulation models [2,3], in which the growth of small perturbations was investigated for various synoptic regimes. Such experiments with perturbed initial conditions for numerical models have led to follow-up ensemble forecasting with various numerical models [4]. While Monte Carlo methods for generating initial conditions had been commonly used in the early stages of ensemble forecasting [5,6], substantial attention was later paid to methods for generating perturbations with dynamical features of the variable fields in the world-leading centres

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Conclusion