Projected changes of wintertime synoptic‐scale transient eddy activities in the East Asian eddy‐driven jet from CMIP5 experiments

The wintertime East Asian eddy‐driven jet (EAEJ) responding to climate change in the 21st century is studied using model outputs from the Coupled Model Intercomparison Project phase 5 (CMIP5). Compared to the location displacement in oceanic eddy‐driven jets, the magnitude change of synoptic‐scale transient eddy activities, measured by eddy kinetic energy (EKE), is a more striking feature in EAEJ. An intensified EKE is projected unanimously by CMIP5 models, suggesting that potential strong winter storm events are likely to happen in East Asian midlatitude in a warming climate. The future change of EKE in EAEJ can be understood in terms of growing baroclinicity wave. The upper level EKE is highly correlated to the low‐level static stability, Brunt‐Väisälä frequency (BVF). CMIP5 models generally project an intensified upper evel EKE with a reduced low‐level BVF (ΔEKE ∝ −ΔBVF). Meanwhile, the enhancement of EKE is also constrained by its historical state (ΔEKE ∝ −EKE). Intermodel variabilities among CMIP5 models reveal a similar but weaker relationship between ΔBVF (or EKE) and ΔEKE, indicating relatively large model diversities and independencies among CMIP5 models.Key PointsThe East Asian eddy‐driven jet will be intensified in a warming climateThe enhancement is related to the surface stability and the historical stateCMIP5 models exhibit large model diversities and independenciesPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/113168/1/grl53203.pd

Large-scale circulation features associated with the heat wave over Northeast China in summer 2018

In late July and early August 2018, Northeast China suffered from extremely high temperatures, with the maxium temperature anomaly exceeding 6°C. In this study, the large-scale circulation features associated with this heat wave over Northeast China are analyzed using station temperature data and NCEP–NCAR reanalysis data. The results indicate that strong anomalous positive geopotential height centers existed from the lower to upper levels over Northeast China, and the related downward motions were directly responsible for the extreme high-temperature anomalies. The northwestward shift of the western Pacific subtropical high (WPSH) and the northeastward shift of the South Asian high concurrently reinforced the geopotential height anomalies and descending flow over Northeast China. In addition, an anomalous Pacific–Japan pattern in the lower troposphere led to the northwestward shift of the WPSH, jointly favoring the anomalous geopotential height over Northeast China. Two wave trains emanating from the Atlantic region propagated eastwards along high latitudes and midlatitudes, respectively, and converged over Northeast China, leading to the enhancement of the geopotential height anomalies

Linking Deep and Shallow Convective Mass Fluxes via an Assumed Entrainment Distribution in CAM5‐CLUBB: Parameterization and Simulated Precipitation Variability

Abstract We modify the Zhang‐McFarlane (ZM) deep convection scheme in the Community Atmosphere Model version 5 to couple it with a unified parameterization for boundary‐layer turbulence and shallow convection, that is, Cloud Layers Unified by Binormals (CLUBB). By assuming a lognormal distribution of entrainment rate across the entire moist convective regimes, we link mass fluxes between shallow and deep convection, which are partitioned by the entrainment rate of the shallowest deep convective plume. Hence, a new deep convective closure is established which is coupled to the sub‐grid vertical motion variability in CLUBB. The convection feedback (or memory) effects are also considered to decrease the entrainment spectrum width and enhance the vertical velocity variability that further affect deep convection. Results show that the revised scheme improves the precipitation simulations in terms of the mean state and variability at various timescales, such as the alleviated double‐intertropical convergence zone and more realistic simulations of the seasonal variation of monsoon precipitation over East Asia, Madden‐Julian Oscillation, and precipitation diurnal phase propagations downstream of large terrains. The improvements are still seen in many aspects such as the mean‐state precipitation when turning off the convection feedback impacts in the revised scheme, emphasizing the benefits of using the modified mass‐flux closure. However, the convection feedbacks have considerable effects on the precipitation diurnal cycle simulations over regions with late‐afternoon precipitation peaks. Overall, the revised scheme provides a unified treatment for sub‐grid vertical motions across regimes of boundary‐layer turbulence, shallow convection, and deep convection, leading to better‐simulated precipitation at various timescales