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Representation of moist convective processes in Coupled Model Intercomparison Project Phase 5 and Phase 6 models for the simulation of Indian summer monsoon intraseasonal variability

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INTERNATIONAL JOURNAL OF CLIMATOLOGY 2022年第16期42卷 8701-8723页

作者： Tirkey, Snehlata Mukhopadhyay, Parthasarathi Krishna, Ravuri Phani Murali Minist Earth Sci Indian Inst Trop Meteorol Dr Homi Bhabha Rd Pune 411008 Maharashtra India Savitribai Phule Pune Univ Dept Atmospher & Space Sci Pune Maharashtra India

This study assesses the simulation of the Boreal Summer Intraseasonal Oscillation (BSISO), particularly the moist convective processes associated with the BSISO in 10 models from phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6). Most of the models show a slower northward propagation of the BSISO and cannot simulate the origin of positive rainfall anomalies over the equatorial Indian Ocean. The generation of barotropic vorticity to the north of the convection centre leads to the northward shift of moisture convergence resulting in the northward propagation of convection. This mechanism is also insufficient in the models. The models show a lack of consistent evolution of moisture with increasing rain rates. Some of the CMIP6 models such as MPI-ESM1-2-LR, FGOALS-f3-L, and NorESM2-MM exhibit better northward propagation and the associated moist processes. A random relationship between vertical velocity, specific humidity, and precipitation is seen in the observation. On the other hand, the models show a deterministic relationship among these parameters with a much higher fraction of convective rain than large-scale rain. Only FGOALS-f3-L (from the CMIP6 family), which uses convection resolving precipitation parameterization, where the convective and stratiform precipitation is calculated explicitly, produces the variability seen in the observation to a large extent.

关键词： Boreal Summer Intraseasonal Oscillations CMIP5 models CMIP6 models convective parameterization

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Effects of Improved Simulation of Precipitation on Evapotranspiration and Its Partitioning Over Land

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GEOPHYSICAL RESEARCH LETTERS 2022年第5期49卷 e2021GL097353-e2021GL097353页

作者： Cui, Zeyu Wang, Yong Zhang, Guang J. Yang, Mengmiao Liu, Jane Wei, Linyi Tsinghua Univ Dept Earth Syst Sci Inst Global Change Studies Minist EducKey Lab Earth Syst Modeling Beijing Peoples R China Scripps Inst Oceanog La Jolla CA 92037 USA Fujian Normal Univ Sch Geog Sci Key Lab Humid Subtrop Ecogeog Proc Minist Educ Fuzhou Peoples R China Univ Toronto Dept Geog & Planning Toronto ON Canada

Evapotranspiration (ET) is a key component of the global hydrological cycle, which is strongly modulated by the occurrence of different rainfall intensities. Global climate models (GCMs) commonly suffer from "too much light rain" and a negative bias in the ratio of transpiration (T) to ET (T/ET). It is unclear whether these biases are related. Here we show that with the improved simulation of probability density functions of rainfall intensity by suppressing light-rain occurrence using a stochastic convection parameterization in the NCAR CESM1.2, the canopy T increases in tropical forests while evaporation from canopy interception and bare soil decreases. The simulated T/ET is increased by 2.5% globally and up to 8% regionally, primarily attributable to reduced fraction of wet leaves due to less frequent light rain despite its weak intensity. These results imply that excessive light rain is an important cause of the negative T/ET bias in GCMs.

关键词： evapotranspiration light rain general circulation models convective parameterization

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Can We Use 1D Models to Predict 3D Model Response to Forcing in an Idealized Framework?

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JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS 2022年第4期14卷 e2021MS002785-e2021MS002785页

作者： Hwong, Y-L Sherwood, S. C. Fuchs, D. Univ New South Wales Climate Change Res Ctr Sydney NSW Australia

Single-column models (SCMs) simulations are sometimes used to evaluate model physics and aid parameterization development. However, few studies have systematically compared SCM behavior-where column boundary conditions are specified-with that of corresponding 3D models, where columns interact dynamically. Here we address this by comparing forced responses of an SCM in radiative-convective equilibrium (RCE) with those of a multi-column model (MCM) where the model domain is in RCE but individual columns are not, examining what factors affect the models' comparability. We find that convective organization in the MCM depends at least as much on the convection scheme as on other mechanisms known to organize convection (e.g., radiative feedback). Moreover, convective organization emerges as a robust factor affecting SCM-MCM comparability, with more aggregated states in 3D associated with larger behavior deviations from the 1D counterpart. This is found across five convection schemes and applies to simulated mean states, linear responses to small tendency perturbations, and adjustments to doubled-CO2 forcing. Nevertheless, we find that even when convection is organized, behavior differences between pairs of schemes in the SCM are largely preserved in the MCM. This indicates that when model physics produces accurate behavior in a 1D setup, it will be more likely to do so in a 3D setup. However, our idealized RCE framework implies that these conclusions may not apply to situations with strong large-scale forcing or encountered over land. Lastly, we demonstrate the practical value of linear responses by showing that they can accurately predict an SCM's tropospheric adjustment to doubled-CO2 forcing.

关键词： model evaluation radiative-convective equilibrium convective parameterization doubled-CO2 convective organization

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On a Solution of the Closure Problem for Dry convective Boundary Layer Turbulence and Beyond

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2022年第5期79卷 1405-1428页

作者： Gryanik, Vladimir M. Hartmann, Joerg Alfred Wegener Inst Helmholtz Zent Polar & Meeresforschung Bremerhaven Germany Russian Acad Sci AM Obukhov Inst Atmospher Phys Moscow Russia

We consider the closure problem of representing the higher-order moments (HOMs) in terms of lower-order moments, a central feature in turbulence modeling based on the Reynolds-averaged Navier-Stokes (RANS) approach. Our focus is on models suited for the description of asymmetric, nonlocal, and semiorganized turbulence in the dry atmospheric convective boundary layer (CBL). We establish a multivariate probability density function (PDF) describing populations of plumes that are embedded in a sea of weaker randomly spaced eddies, and apply an assumed delta-PDF approximation. The main content of this approach consists of capturing the bulk properties of the PDF. We solve the closure problem analytically for all relevant HOMs involving velocity components and temperature and establish a hierarchy of new non-Gaussian turbulence closure models of different content and complexity ranging from analytical to semianalytical. All HOMs in the hierarchy have a universal and simple functional form. They refine the widely used Millionshchikov closure hypothesis and generalize the famous quadratic skewness-kurtosis relationship to higher order. We examine the performance of the new closures by comparison with measurement, LES, and DNS data and derive empirical constants for semianalytical models, which are best for practical applications. We show that the new models have a good skill in predicting the HOMs for atmospheric CBL. Our closures can be implemented in second-, third-, and fourth-order RANS turbulence closure models of bi-, tri-, and four-variate levels of complexity. Finally, several possible generalizations of our approach are discussed.

关键词： Atmosphere Boundary layer convective parameterization Eddies parameterization Turbulence Updrafts downdrafts

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A Decentralized Approach for Modeling Organized Convection Based on Thermal Populations on Microgrids

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JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS 2022年第10期14卷 e2022MS003042-e2022MS003042页

作者： Neggers, R. A. J. Griewank, P. J. Univ Cologne Inst Geophys & Meteorol Cologne Germany Univ Vienna Dept Meteorol & Geophys Vienna Austria

In this study, a spectral model for convective transport is coupled to a thermal population model on a two-dimensional horizontal "microgrid," covering the typical gridbox size of general circulation models. The goal is to explore new ways of representing impacts of spatial organization in cumulus cloud fields. The thermals are considered the smallest building block of convection, with thermal life cycle and movement represented through binomial functions. Thermals interact through two simple rules, reflecting pulsating growth and environmental deformation. Long-lived thermal clusters thus form on the microgrid, exhibiting scale growth and spacing that represent simple forms of spatial organization and memory. Size distributions of cluster number are diagnosed from the microgrid through an online clustering algorithm, and provided as input to a spectral multiplume eddy-diffusivity mass flux scheme. This yields a decentralized transport system, in that the thermal clusters acting as independent but interacting nodes that carry information about spatial structure. The main objectives of this study are (a) to seek proof of concept of this approach, and (b) to gain insight into impacts of spatial organization on convective transport. Single-column model experiments demonstrate satisfactory skill in reproducing two observed cases of continental shallow convection. Metrics expressing self-organization and spatial organization match well with large-eddy simulation results. We find that in this coupled system, spatial organization impacts convective transport primarily through the scale break in the size distribution of cluster number. The rooting of saturated plumes in the subcloud mixed layer plays a key role in this process. Plain Language Summary Recent studies have emphasized the importance of the spatial structure of convective cloud fields in Earth's climate, yet this phenomenon is not yet represented well in Earth System Models (ESMs). This study explores a new way

关键词： convective parameterization spatial organization population dynamics thermals microgrid modeling shallow cumulus

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Idealized Simulations of the Tropical Climate and Variability in the Single Column Atmosphere Model (SCAM): Radiative-convective Equilibrium

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JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS 2022年第2期14卷

作者： Hu, I-Kuan Mapes, Brian E. Tulich, Stefan N. Neale, Richard B. Gettelman, Andrew Reed, Kevin A. Univ Colorado Cooperat Inst Res Environm Sci Boulder CO 80309 USA NOAA Phys Sci Lab Boulder CO 80309 USA Univ Miami Rosenstiel Sch Marine & Atmospher Sci Miami FL USA Natl Ctr Atmospher Res Climate & Global Dynam Lab POB 3000 Boulder CO 80307 USA SUNY Stony Brook Sch Marine & Atmospher Sci Stony Brook NY 11794 USA

To explore the interactions among column processes in the Community Atmosphere Model (CAM), the single-column version of CAM (SCAM) is integrated for 1000 days in radiative-convective equilibrium (RCE) with tropical values of boundary conditions, spanning a parameter or configuration space of model physics versions (v5 vs. v6), vertical resolution (standard and 60 levels), sea surface temperature (SST), and some interpretation-driven experiments. The simulated time-mean climate is reasonable, near observations and RCE of a cyclic cloud-resolving model. Updraft detrainment in the deep convection scheme produces distinctive grid-scale structures in humidity and cloud, which also interact with radiative transfer processes. These grid artifacts average out in multi-column RCE results reported elsewhere, illustrating the nuts-and-bolts interpretability that SCAM adds to the hierarchy of model configurations. Multi-day oscillations of precipitation arise from descent of warm convection-capping layers starting near the tropopause, eventually reset by a burst of convective deepening. Experiments reveal how these oscillations depend critically on an internal parameter that controls the number of neutral buoyancy levels allowed for determining cloud top and computing dilute convective available potential energy in the deep convection scheme, and merely modified a little by disabling cloud-base radiation (heating of cloud base). This strong dependence of transient behavior in 1D on this parameter will be tested in the second part of this work, in which SCAM is coupled to a parameterized dynamics of two-dimensional, linearized gravity wave, and in the 3D simulations in future study.

关键词： convective parameterization radiative-convective equilibrium climate model hierarchy

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A Prognostic-Stochastic and Scale-Adaptive Cumulus Convection Closure for Improved Tropical Variability and convective Gray-Zone Representation in NOAA's Unified Forecast System (UFS)

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MONTHLY WEATHER REVIEW 2022年第12期150卷 3211-3227页

作者： Bengtsson, Lisa Gerard, Luc Han, Jongil Gehne, Maria Li, Wei Dias, Juliana NOAA Phys Sci Lab ESRL Boulder CO 80305 USA Royal Meteorol Inst Brussels Belgium NOAA Environm Modeling Ctr NCEP College Pk MD USA Univ Colorado Boulder Cooperat Inst Res Environm Sci Boulder CO USA NOAA Environm Modeling Ctr IM Syst Grp NCEP College Pk MD USA

A prognostic closure is introduced to, and evaluated in, NOAA's Unified Forecast System. The closure addresses aspects that are not commonly represented in traditional cumulus convection parameterizations, and it departs from the previous assumptions of a negligible subgrid area coverage and statistical quasi-equilibrium at steady state, the latter of which becomes invalid at higher resolution. The new parameterization introduces a prognostic evolution of the convective updraft area fraction based on a moisture budget, and, together with the buoyancy-driven updraft vertical velocity, it completes the cloud-base mass flux. In addition, the new closure addresses stochasticity and includes a representation of subgrid convective organization using cellular automata as well as scale-adaptive considerations. The new cumulus convection closure shows potential for improved Madden-Julian oscillation (MJO) prediction. In our simulations we observe better propagation, amplitude, and phase of the MJO in a case study relative to the control simulation. This improvement can be partly attributed to a closer coupling between low-level moisture flux convergence and precipitation as revealed by a space-time coherence spectrum. In addition, we find that enhanced organization feedback representation and stochastic effects, represented using cellular automata, further enhance the amplitude and propagation of the MJO, and they provide realistic uncertainty estimates of convectively coupled equatorial waves at seasonal time scales. The scale-adaptive behavior of the scheme is also studied by running the global model with 25-, 13-, 9-, and 3-km grid spacing. It is found that the convective area fraction and the convective updraft velocity are both scale adaptive, leading to a reduction of subgrid convective precipitation in the higher-resolution simulations.

关键词： convective parameterization Cumulus clouds Stochastic models

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Atmospheric Convection

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ATMOSPHERE-OCEAN 2022年第3-4期60卷 422-476页

作者： Lin, Jialin Qian, Taotao Bechtold, Peter Grell, Georg Zhang, Guang J. Zhu, Ping Freitas, Saulo R. Barnes, Hannah Han, Jongil Ohio State Univ Dept Geog Columbus OH 43210 USA European Ctr Medium Range Weather Forecast Shinfield England European Ctr Medium Range Weather Forecast Bologna Italy European Ctr Medium Range Weather Forecast Bonn Germany NOAA Global Syst Lab Boulder CO 80305 USA Univ Calif San Diego Scripps Inst Oceanog CASPO San Diego CA 92093 USA Florida Int Univ Dept Earth & Environm Miami FL 33199 USA Natl Inst Space Res Sao Paulo Brazil NOAA CIRES Global Syst Lab Boulder CO 80305 USA NOAA NCEP Environm Modeling Ctr College Pk MD 20740 USA

convective parameterization is the long-lasting bottleneck of global climate modelling and one of the most difficult problems in atmospheric sciences. Uncertainty in convective parameterization is the leading cause of the widespread climate sensitivity in IPCC global warming projections. This paper reviews the observations and parameterizations of atmospheric convection with emphasis on the cloud structure, bulk effects, and closure assumption. The representative state-of-the-art convection schemes are presented, including the ECMWF convection scheme, the Grell scheme used in NCEP model and WRF model, the Zhang-MacFarlane scheme used in NCAR and DOE models, and parameterizations of shallow moist convection. The observed convection has self-suppression mechanisms caused by entrainment in convective updrafts, surface cold pool generated by unsaturated convective downdrafts, and warm and dry lower troposphere created by mesoscale downdrafts. The post-convection environment is often characterized by "diamond sounding" suggesting an over-stabilization rather than barely returning to neutral state. Then the pre-convection environment is characterized by slow moistening of lower troposphere triggered by surface moisture convergence and other mechanisms. The over-stabilization and slow moistening make the convection events episodic and decouple the middle/upper troposphere from the boundary layer, making the state-type quasi-equilibrium hypothesis invalid. Right now, unsaturated convective downdrafts and especially mesoscale downdrafts are missing in most convection schemes, while some schemes are using undiluted convective updrafts, all of which favour easily turned-on convection linked to double-ITCZ (inter-tropical convergence zone), overly weak MJO (Madden-Julian Oscillation) and precocious diurnal precipitation maximum. We propose a new strategy for convection scheme development using reanalysis-driven model experiments such as the assimilation runs in weather predicti

关键词： atmospheric convection convective parameterization global climate modelling weather prediction

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Evaluation of Three Genesis Potential Indices for Tropical Cyclogenesis in the Arabian Sea: Two Case Studies Using WRF and ERA5

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MONTHLY WEATHER REVIEW 2022年第12期150卷 3275-3303页

作者： Ikram, Farah Ullah, Kalim Chen, Deliang Res & Dev Div Pakistan Meteorol Dept Islamabad Pakistan COMSATS Univ Islamabad Dept Meteorol Islamabad Pakistan Univ Gothenburg Dept Earth Sci Reg Climate Grp Gothenburg Sweden

Tropical cyclones (TCs) generated over the Arabian Sea can cause significant damage to infrastructure, human lives, landfall, and property near inshore and maritime trade route areas. A key to successful prediction of TCs is a skillful prediction of potential cyclogenesis locations. This study focuses on evaluating three genesis potential indices (GPIs) derived from a global reanalysis (ERA5) and dynamically downscaling using a regional model (WRF) for two TC cases: Gonu in 2007 and Kyarr in 2019, selected by analyzing the accumulated cyclone energy trend from the International Best Track Archive for Climate Stewardship (IBTrACS) dataset over the period of 1981-2019. The two TCs belong to category 4 and above on the Saffir-Simpson scale. To test the sensitivity of downscaling to cumulus parameterizations, two WRF experiments were conducted using the Kain-Fritsch and New Tiedke cumulus schemes, respectively. The calculated genesis locations with help of the three GPIs were compared with IBTrACS. The results show that 1) all indices have reasonable skills in reproducing genesis locations, although their performances differ somewhat;2) the dynamic downscaling with two WRF experiments added value to the study by comparing two numerical schemes for estimating genesis locations;and 3) WRF with the New Tiedke and Kain-Fritsch schemes showed good skill in reproducing the spatial distribution of the most relevant dynamical parameters. The pattern correlations are well correlated with environmental parameters of untransformed GPI and higher correlations with binary logarithmic transformed GPI. The applicability to other cyclones is also tested (e.g., TC Nilofar in 2014) with encouraging results. This study demonstrates the usefulness of GPIs for forecasting TC genesis in the region. Significance StatementThe trend analysis of accumulated cyclone energy (ACE) over the Arabian Sea (AS) shows an increase over the period of 1981-2019 with the highest ACE values for 2019. The gene

关键词： Asia Cyclogenesis cyclolysis Mesoscale processes convective parameterization Mesoscale models

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Impact of Cumulus Options from Weather Research and Forecasting with Chemistry in Atmospheric Modeling in the Andean Region of Southern Ecuador

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ATMOSPHERE 2024年第6期15卷 693页

作者： Parra, Rene Univ San Francisco Quito USFQ Colegio Ciencias & Ingn Inst Simulac Computac ISC USFQ Quito 170901 Ecuador

Cumulus parameterization schemes model the subgrid-scale effects of moist convection, affecting the prognosis of cloud formation, rainfall, energy levels reaching the surface, and air quality. Working with a spatial resolution of 1 km, we studied the influence of cumulus parameterization schemes coded in the Weather Research and Forecasting with Chemistry Version 3.2 (WRF-Chem 3.2) for modeling in an Andean city in Southern Ecuador (Cuenca, 2500 masl), during September 2014. To assess performance, we used meteorological records from the urban area and stations located mainly over the Cordillera, with heights above 3000 masl, and air quality records from the urban area. Firstly, we did not use any cumulus parameterization (0 No Cumulus). Then, we considered four schemes: 1 Kain-Fritsch, 2 Betts-Miller-Janjic, 3 Grell-Devenyi, and 4 Grell-3 Ensemble. On average, the 0 No Cumulus option was better for modeling meteorological variables over the urban area, capturing 66.5% of records and being the best for precipitation (77.8%). However, 1 Kain-Fritsch was better for temperature (78.7%), and 3 Grell-Devenyi was better for wind speed (77.0%) and wind direction (37.9%). All the options provided acceptable and comparable performances for modeling short-term and long-term air quality variables. The results suggested that using no cumulus scheme could be beneficial for holistically modeling meteorological and air quality variables in the urban area. However, all the options, including deactivating the cumulus scheme, overestimated the total amount of precipitation over the Cordillera, implying that its modeling needs to be improved, particularly for studies on water supply and hydrological management. All the options also overestimated the solar radiation levels at the surface. New WRF-Chem versions and microphysics parameterization, the other component directly related to cloud and rainfall processes, must be assessed. In the future, a more refined inner domain, or an inner

关键词： Cuenca convective parameterization cumulus convective rainfall

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