Abstract
This study investigates the practical predictability of two simulated mesoscale convective systems (MCS1 and MCS2) within a state-of-the-art convection-allowing ensemble forecast system. The two MCSs are both controlled by the synoptic Meiyu-front but differ in mesoscale orographic forcing. An observation system simulation experiment (OSSE) setup is first built, which includes flow-dependent multiple-scale initial and lateral boundary perturbations and a 12 h 30-member ensemble forecast is thereby created. In combination with the difference total energy, the decorrelation scale and the ensemble sensitivity analysis, both forecast error evolution, precipitation uncertainties and meteorological sensitivity that describe the practical predictability are assessed. The results show large variabilities of precipitation forecasts among ensemble members, indicative of the practical predictability limit. The study of forecast error evolution shows that the error energy in the MCS1 region in which the convection is blocked by the Dabie Mountains exhibits a simultaneous peak pattern for all spatial scales at around 6 h due to strong moist convection. On the other hand, when large-scale flow plays a more important role, the forecast error energy in the MCS2 region exhibits a stepwise increase with increasing spatial scale. As a result of error energy growth, the precipitation uncertainties evolve from small scales and gradually transfer to larger scales, implying a strong relationship between error growth and precipitation across spatial scales, thus explaining the great precipitation variability within ensemble members. These results suggest the additional forcing brought by the Dabie Mountains could regulate the predictability of Meiyu-frontal convection, which calls for a targeted perturbation design in convection-allowing ensemble forecast systems with respect to different forcing mechanisms.
Highlights
Forecasting warm-season convective events is a consistent important and challenging issue during the most recent decades over the Yangtze and Huai River Basin (YHRB) [1,2]
In a step forward, we present the scale-dependent forecast error growth and explore how error energy evolution could impact the diagnostic precipitation variable, which could explain the precipitation variability within ensemble forecasts
118.5◦ (Figure 9i), causing a greater upward motion. These results reveal that the accurate forecasting of the strength of the synoptic low-level jet (Figure 2a–e) is responsible for the precipitation forecast in the MCS2 region
Summary
Forecasting warm-season convective events is a consistent important and challenging issue during the most recent decades over the Yangtze and Huai River Basin (YHRB) [1,2]. Zhuang et al [12] systematically explored and compared the spatial predictability under different convective regimes (strongly- and weakly-forced regimes) over YHRB using convection-allowing ensembles produced by an observation system simulation experiment (OSSE) framework They did not consider the specific condition when synoptic frontal and orographic forcing simultaneously exist. Synoptic frontal forced precipitation, lead to different error growth dynamics and produces different precipitation uncertainties To this end, three main questions are addressed: 1) what is the precipitation forecast sensitivity with respect to thermodynamic states at initial/previous times of a typical frontal precipitation system and that influenced by the Dabie Mountains; 2) considering multiple-scale errors induced from initial and lateral boundary condition, what is the evolution characteristics of forecast error? 2. Data and Methods the presence of Dabie Mountains could substantially impact the practical predictability of synoptic frontal forced precipitation, lead to different error growth dynamics and produces different. The blue square marks the general range of synoptic low-level jet while the orange square marks the range of boundary layer low-level jet
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
