Impacts of spatially distributed precipitation and soil heterogeneity on modeling water fluxes at different spatial resolutions are investigated using the Three-layer Variable Infiltration Capacity ...(VIC-3L) land surface model at the Blue River watershed in Oklahoma. In this study, hourly grid-based NEXRAD (Next Generation Radar) Stage III radar precipitation data approximately at 4×4 km
2 resolution are used to compute daily precipitation at spatial resolutions of 1/32, 1/16, 1/8, 1/4, 1/2 and 1 degree based on an area weighted average method. Soil parameters at the corresponding six spatial resolutions are derived from the State Soil Geographic (STATSGO) soil data. The forcing data of daily maximum and minimum temperature, wind speed, and vegetation parameters are disaggregated/aggregated directly to finer/coarser spatial resolutions based on the University of Washington (UW) data, which are gridded at 1/8 degree spatial resolution. Our study suggests that a critical spatial resolution for the VIC-3L model may exist for the study watershed. For spatial resolutions finer than the critical resolution, one does not necessarily obtain better model performance in terms of runoff, evapotranspiration, and total zone soil moisture with increasing spatial resolution if the VIC-3L model parameters are calibrated at each spatial resolution. Also, model parameters calibrated at a coarse resolution can be applied to finer resolutions to obtain generally comparable results. However, model parameters calibrated at finer resolutions cannot result in comparable results when applied to resolutions coarser than the identified critical resolution. In addition, while soil moisture of the total zone is more sensitive to the spatial distributions of soil properties, runoff and evaporation are more sensitive to the spatial distribution of daily precipitation at the watershed being studied.
Abstract
The future state of the global water cycle and prediction of freshwater availability for humans around the world remain among the challenges of climate research and are relevant to several ...United Nations Sustainable Development Goals. The Global Precipitation EXperiment (GPEX) takes on the challenge of improving the prediction of precipitation quantity, phase, timing and intensity, characteristics that are products of a complex integrated system. It will achieve this by leveraging existing World Climate Research Programme (WCRP) activities and community capabilities in satellite, surface-based, and airborne observations, modeling and experimental research, and by conducting new and focused activities. It was launched in October 2023 as a WCRP Lighthouse Activity. Here we present an overview of the GPEX Science Plan that articulates the primary science questions related to precipitation measurements, process understanding, model performance and improvements, and plans for capacity development. The central phase of GPEX is the WCRP Years of Precipitation for 2-3 years with coordinated global field campaigns focusing on different storm types (atmospheric rivers, mesoscale convective systems, monsoons, and tropical cyclones, among others) over different regions and seasons. Activities are planned over the three phases (before, during, and after the Years of Precipitation) spanning a decade. These include gridded data evaluation and development, advanced modeling, enhanced understanding of processes critical to precipitation, multi-scale prediction of precipitation events across scales, and capacity development. These activities will be further developed as part of the GPEX Implementation Plan.
Abstract
The observed stratospheric quasi‐biennial oscillation (QBO) and the tropospheric Madden‐Julian oscillation (MJO) are strongly connected in boreal winter, with stronger MJO activity when ...lower‐stratospheric winds are easterly. However, the current generation of climate models with internally generated representations of the QBO and MJO do not simulate the observed QBO‐MJO connection, for reasons that remain unclear. This study builds on prior work exploring the QBO‐MJO link in climate models whose stratospheric winds are relaxed toward reanalysis, reducing stratospheric biases in the model and imposing a realistic QBO. A series of ensemble experiments are performed using four state‐of‐the‐art climate models capable of representing the MJO over the period 1980–2015, each with similar nudging in the stratosphere. In these four models, nudging leads to a good representation of QBO wind and temperature signals, however no model simulates the observed QBO‐MJO relationship. Biases in MJO vertical structure and cloud‐radiative feedbacks are investigated, but no conclusive model bias or mechanism is identified that explains the lack of a QBO‐MJO connection.
Accurate simulations of air quality and climate require robust model parameterizations on regional and global scales. The Weather Research and Forecasting model with Chemistry version 3.4.1 has been ...coupled with physics packages from the Community Atmosphere Model version 5 (CAM5) (WRF-CAM5) to assess the robustness of the CAM5 physics package for regional modeling at higher grid resolutions than typical grid resolutions used in global modeling. In this two-part study, Part I describes the application and evaluation of WRF-CAM5 over East Asia at a horizontal resolution of 36-km for six years: 2001, 2005, 2006, 2008, 2010, and 2011. The simulations are evaluated comprehensively with a variety of datasets from surface networks, satellites, and aircraft. The results show that meteorology is relatively well simulated by WRF-CAM5. However, cloud variables are largely or moderately underpredicted, indicating uncertainties in the model treatments of dynamics, thermodynamics, and microphysics of clouds/ices as well as aerosol-cloud interactions. For chemical predictions, the tropospheric column abundances of CO, NO2, and O3 are well simulated, but those of SO2 and HCHO are moderately overpredicted, and the column HCHO/NO2 indicator is underpredicted. Large biases exist in the surface concentrations of CO, NO2, and PM10 due to uncertainties in the emissions as well as vertical mixing. The underpredictions of NO lead to insufficient O3 titration, thus O3 overpredictions. The model can generally reproduce the observed O3 and PM indicators. These indicators suggest to control NOx emissions throughout the year, and VOCs emissions in summer in big cities and in winter over North China Plain, North/South Korea, and Japan to reduce surface O3, and to control SO2, NH3, and NOx throughout the year to reduce inorganic surface PM.
Two sets of 48‐h hindcast experiments for Mei‐yu season using non‐hydrostatic global variable‐resolution model (MPAS‐Atmosphere) with regional refinement at 4 km resolution (V4km) and uniform 60 km ...resolution (U60km) are first‐time conducted to attempt at simulating the Mei‐yu rainfall in 2015 over East China. The analysis focuses on the seasonal average of diurnal variation of precipitation amount (PA), intensity (PI), and frequency (PF). Both simulations reasonably reproduce the spatial distribution of PA. V4km is more skillful in simulating the spatial distributions and magnitudes of PF and PI. The diurnal cycle of Mei‐yu rainfall shows a major early morning peak and a minor afternoon peak, contributed by precipitation during two sub‐periods with distinct synoptic circulations. With strong Mei‐yu in the first sub‐period, the diurnal variation of PA is controlled by nocturnal southwesterly jet. V4km overestimates the morning peak mainly due to its bias in simulating boundary layer inertial oscillation. Although differences in PA between the simulations are small, U60km overestimates PF and underestimates PI. With weak Mei‐yu in the second sub‐period, the diurnal variation of PA is controlled by both synoptic circulation and local convection. At both resolutions, deviations in the large‐scale circulation modulated by a few typhoons lead to positive biases in the morning peak of PA. After removing the typhoon impacts, V4km captures the observed diurnal cycle of PA well, while U60km significantly underestimates PA and PI particularly in the afternoon. Future studies focusing on advancing modeling of southwesterly jet and typhoons may further improve convection permitting simulation of Mei‐yu rainfall.
Key Points
Global modeling at V4km is more skillful in reproducing Mei‐yu rainfall characteristics compared to modeling at U60km
With strong Mei‐yu, differences in rainfall diurnal variation controlled by nocturnal southwesterly jet are small between U60km and V4km
With weak Mei‐yu, V4km produces better rainfall diurnal variation controlled by multi‐scale processes compared to U60km
This study aims to further understand the environments supporting summer mesoscale convective system (MCS) initiation in the U.S. Great Plains. A self‐organizing map analysis is conducted to identify ...four types of summer MCS initiation environments during 2004–2017: Type‐1 and Type‐2 feature favorable large‐scale environments, Type‐3 has favorable lower‐level and surface conditions but unfavorable upper‐level circulation, while Type‐4 features the most unfavorable large‐scale environments. Despite the unfavorable large‐scale environment, convection‐centered composites reveal the presence of favorable sub‐synoptic scale environments for MCS initiation in Type‐3 and Type‐4. All four types of MCS initiation environments delineate clear eastward propagating features in many meteorological fields, such as potential vorticity, surface pressure, and equivalent potential temperature, upstream up to 25° west of and ∼36 h before MCS initiation. While the propagating environments and local, non‐propagating low‐level moisture are important to MCS initiation at the foothill of the Rocky Mountains, MCS initiation in the Great Plains is supported by the coupled dynamical and moisture anomalies, both associated with eastward propagating waves. Hence, MCSs initiated in the plains can produce more rainfall than those initiated at the foothill due to a more abundant moisture supply. By tracking MCSs and mid‐tropospheric perturbations (MPs), a unique type of sub‐synoptic disturbances with Rocky Mountains origin, it is shown that ∼30% of MPs are associated with MCS initiation, mostly in Type‐4. Although MPs are related to a small fraction of MCS initiation, MCSs that are associated with MPs tend to produce more rainfall in a larger area with a stronger convective intensity.
Plain Language Summary
During spring and summer, organized and traveling thunderstorms are commonplace in the U.S. Great Plains. While these thunderstorms contribute considerably to the seasonal rainfall, the summertime thunderstorm initiation is less well understood because the large‐scale meteorological patterns are substantially weaker in summer than spring and the smaller‐scale perturbations become more important but are harder to capture by the sparse observation network. Here, we combine newly developed tracking records of these traveling thunderstorms with a modern atmospheric data set to examine the thunderstorm initiation environments in summer. We find that eastward propagating environment exist several days before the thunderstorm initiation. The relative importance of the ingredients in the propagating environments to thunderstorm initiation changes from the foothill of the Rocky Mountains to the central plains as the coupling between moisture and wind pattern becomes increasingly critical. Hence, at the beginning several hours of thunderstorms, their rainfall is heavier in the plains due to more moisture supply, compared to thunderstorms initiated at the foothill. With available data of a unique type of weather disturbances originated from the Rocky Mountains, we are able to quantify the contribution of this type of disturbances to the summertime thunderstorm initiation.
Key Points
Summer mesoscale convective systems (MCSs) in the U.S. Great Plains can initiate under unfavorable large‐scale environments when favorable sub‐synoptic forcing is present
Eastward propagation is found for both large‐scale and sub‐synoptic environments, up to 25° west of and 36 h prior to MCS initiation
About 30% of mid‐tropospheric perturbations originated from the Rocky Mountains initiate intense MCSs under weak large‐scale forcing
PDF
