scholarly journals Assessing Impacts of PBL and Surface Layer Schemes in Simulating the Surface–Atmosphere Interactions and Precipitation over the Tropical Ocean Using Observations from AMIE/DYNAMO

2016 ◽  
Vol 29 (22) ◽  
pp. 8191-8210 ◽  
Author(s):  
Yun Qian ◽  
Huiping Yan ◽  
Larry K. Berg ◽  
Samson Hagos ◽  
Zhe Feng ◽  
...  
Keyword(s):  
Surface Layer ◽  
Climate Models ◽  
Deep Convection ◽  
Surface Wind ◽  
Wrf Model ◽  
Surface Fluxes ◽  
Shallow Convection ◽  
Free Atmosphere ◽  
Tropical Ocean ◽  
Surface Atmosphere

Abstract Accuracy of turbulence parameterization in representing planetary boundary layer (PBL) processes and surface–atmosphere interactions in climate models is critical for predicting the initiation and development of clouds. This study 1) evaluates WRF Model–simulated spatial patterns and vertical profiles of atmospheric variables at various spatial resolutions and with different PBL, surface layer, and shallow convection schemes against measurements; 2) identifies model biases by examining the moisture tendency terms contributed by PBL and convection processes through nudging experiments; and 3) investigates the main causes of these biases by analyzing the dependence of modeled surface fluxes on PBL and surface layer schemes over the tropical ocean. The results show that PBL and surface parameterizations have surprisingly large impacts on precipitation and surface moisture fluxes over tropical oceans. All of the parameterizations tested tend to overpredict moisture in the PBL and free atmosphere and consequently result in larger moist static energy and precipitation. Moisture nudging tends to suppress the initiation of convection and reduces the excess precipitation. The reduction in precipitation bias in turn reduces the surface wind and latent heat (LH) flux biases, which suggests the positive feedback between precipitation and surface fluxes is responsible, at least in part, for the model drifts. The updated Kain–Fritsch cumulus potential (KF-CuP) shallow convection scheme tends to suppress the deep convection, consequently decreasing precipitation. The Eta Model surface layer scheme predicts more reasonable LH fluxes and LH–wind speed relationship than those for the MM5 scheme. The results help us identify sources of biases of current parameterization schemes in reproducing PBL processes, the initiation of convection, and intraseasonal variability of precipitation.

scholarly journals Cumulus over the Tibetan Plateau in the Summer Based on CloudSat–CALIPSO Data

2016 ◽  
Vol 29 (3) ◽  
pp. 1219-1230 ◽  
Author(s):  
Yunying Li ◽  
Minghua Zhang
Keyword(s):  
Tibetan Plateau ◽  
Climate Models ◽  
Surface Wind ◽  
Lower Atmosphere ◽  
The Tibetan Plateau ◽  
Shallow Convection ◽  
Free Atmosphere ◽  
Northern Summer ◽  
Static Energy ◽  
Fine Resolution

Abstract Cumulus (Cu) can transport heat and water vapor from the boundary layer to the free atmosphere, leading to the redistribution of heat and moist energy in the lower atmosphere. This paper uses the fine-resolution CloudSat–CALIPSO product to characterize Cu over the Tibetan Plateau (TP). It is found that Cu is one of the dominant cloud types over the TP in the northern summer. The Cu event frequency, defined as Cu occurring within 50-km segments, is 54% over the TP in the summer, which is much larger over the TP than in its surrounding regions. The surface wind vector converging at the central TP and the topographic forcing provide the necessary moisture and dynamical lifting of convection over the TP. The structure of the atmospheric moist static energy shows that the thermodynamical environment over the northern TP can be characterized as having weak instability, a shallow layer of instability, and lower altitudes for the level of free convection. The diurnal variation of Cu with frequency peaks during the daytime confirms the surface thermodynamic control on Cu formation over the TP. This study offers insights into how surface heat is transported to the free troposphere over the TP and provides an observational test of climate models in simulating shallow convection over the TP.

scholarly journals Effects of Land Surface Schemes on WRF-Simulated Geopotential Heights over China in Summer 2003*

2016 ◽  
Vol 17 (3) ◽  
pp. 829-851 ◽  
Author(s):  
Xin-Min Zeng ◽  
B. Wang ◽  
Y. Zhang ◽  
Y. Zheng ◽  
N. Wang ◽  
...  
Keyword(s):  
Land Surface ◽  
Climate Models ◽  
Regional Climate ◽  
Sensible Heat Flux ◽  
Wrf Model ◽  
Surface Fluxes ◽  
Forecast Errors ◽  
Large Area ◽  
Pressure Fields ◽  
Temperature And Pressure

Abstract To quantify and explain effects of different land surface schemes (LSSs) on simulated geopotential height (GPH) fields, we performed simulations over China for the summer of 2003 using 12-member ensembles with the Weather Research and Forecasting (WRF) Model, version 3. The results show that while the model can generally simulate the seasonal and monthly mean GPH patterns, the effects of the LSS choice on simulated GPH fields are substantial, with the LSS-induced differences exceeding 10 gpm over a large area (especially the northwest) of China, which is very large compared with climate anomalies and forecast errors. In terms of the assessment measures for the four LSS ensembles [namely, the five-layer thermal diffusion scheme (SLAB), the Noah LSS (NOAH), the Rapid Update Cycle LSS (RUC), and the Pleim–Xiu LSS (PLEX)] in the WRF, the PLEX ensemble is the best, followed by the NOAH, RUC, and SLAB ensembles. The sensitivity of the simulated 850-hPa GPH is more significant than that of the 500-hPa GPH, with the 500-hPa GPH difference fields generally characterized by two large areas with opposite signs due to the smoothly varying nature of GPHs. LSS-induced GPH sensitivity is found to be higher than the GPH sensitivity induced by atmospheric boundary layer schemes. Moreover, theoretical analyses show that the LSS-induced GPH sensitivity is mainly caused by changes in surface fluxes (in particular, sensible heat flux), which further modify atmospheric temperature and pressure fields. The temperature and pressure fields generally have opposite contributions to changes in the GPH. This study emphasizes the importance of choosing and improving LSSs for simulating seasonal and monthly GPHs using regional climate models.

scholarly journals Sensitivity of inferred regional CO source estimates to the vertical structure in CO as observed by MOPITT

2014 ◽  
Vol 14 (16) ◽  
pp. 22939-22984 ◽  
Author(s):  
Z. Jiang ◽  
D. B. A. Jones ◽  
H. M. Worden ◽  
D. K. Henze
Keyword(s):  
Surface Layer ◽  
North America ◽  
Vertical Structure ◽  
Deep Convection ◽  
A Priori ◽  
Convective Transport ◽  
Vertical Transport ◽  
Surface Fluxes ◽  
Free Troposphere ◽  
The Impact

Abstract. Vertical transport of surface emission to the free troposphere, usually associated with frontal lifting in warm conveyor belts or ascent in deep convection, has significant influence on the vertical structure of atmospheric trace gases. Consequently, it may impact estimates of the surface fluxes of these gases inferred from remote sensing observations that are based on thermal infrared radiances (TIR), since these measurements are sensitive mainly to signals in the free troposphere. In this work, we assessed the sensitivity of regional CO source estimates to the vertical CO distribution, by assimilating multi-spectral MOPITT V5J CO retrievals with the GEOS-Chem model. We compared the source estimates obtained by assimilating the CO profiles and the surface layer retrievals from June 2004 to May 2005. The inversion analyses all produced a reduction in CO emissions in the tropics and subtropics and an increase in the extratropics. The tropical decreases were particularly pronounced for regions where the biogenic source of CO was dominant, suggesting an overestimate of the a priori isoprene source of CO in the model. We found that the differences between the regional source estimates inferred from the profile and surface layer retrievals for 2004–2005 were small, generally less than 5% for the main continental regions, except for estimates for South Asia, North America, and Europe. Because of discrepancies in convective transport in the model, the CO source estimates for India and Southeast Asia inferred from the CO profiles were significantly higher than those estimated from the surface layer retrievals during June–August 2004. On the other hand, the profile inversion underestimated the CO emissions from North America and Europe compared to the assimilation of the surface layer retrievals. We showed that vertical transport of air from the North American and European boundary layer is slower than from other continental regions and thus air in the free troposphere from North America and Europe is more chemically aged, which could explain the discrepancy between the source estimates inferred from the profile and surface layer retrievals. We also examined the impact of the OH distribution on the source estimates using OH fields from versions v5-07-08 and v8-02-01 of GEOS-Chem. The impact of the different OH fields was particularly large for the extratropical source estimates. For example, for North America, using the surface layer retrievals, we estimated a total CO source of 37 and 55 Tg CO with the v5-07-08 and v8-02-01 OH fields, respectively, for June–August 2004. For Europe the source estimates were 57 and 72 Tg CO, respectively. We found that the discrepancies between the source estimates obtained with the two OH fields were larger when using the profile data, which is consistent with greater sensitivity to the more chemically aged air in the free troposphere. Our findings indicate that regional CO source estimates are sensitive to the vertical CO structure. They suggest that assimilating a broader range of composition measurements to provide better constraint on tropospheric OH and the biogenic sources of CO is essential for reliable quantification of the regional CO budget.

scholarly journals Impacts of Vertical Structure of Convection in Global Warming: The Role of Shallow Convection

2016 ◽  
Vol 29 (12) ◽  
pp. 4665-4684 ◽  
Author(s):  
Chao-An Chen ◽  
Jia-Yuh Yu ◽  
Chia Chou
Keyword(s):  
Global Warming ◽  
Climate Models ◽  
Global Climate ◽  
Deep Convection ◽  
Atmospheric Stability ◽  
Detailed Examination ◽  
Global Climate Models ◽  
Shallow Convection ◽  
Tropical Circulation ◽  
Heavy Structure

Abstract Global-warming-induced changes in regional tropical precipitation are usually associated with changes in the tropical circulation, which is a dynamic contribution. This study focuses on the mechanisms of the dynamic contribution that is related to the partition of shallow convection in tropical convection. To understand changes in tropical circulation and its associated mechanisms, 32 coupled global climate models from CMIP3 and CMIP5 were investigated. The study regions are convection zones with positive precipitation anomalies, where both enhanced and reduced ascending motions are found. Under global warming, an upward-shift structure of ascending motion is observed in the entire domain, implying a deepening of convection and a more stable atmosphere, which leads to a weakening of the tropical circulation. In a more detailed examination, areas with enhanced (weakened) ascending motion are associated with more (less) import of moist static energy by a climatologically bottom-heavy (top heavy) structure of vertical velocity, which is similar to a “rich get richer” mechanism. In a warmer climate, different climatological vertical profiles tend to induce different changes in atmospheric stability: the bottom-heavy (top heavy) structure brings a more (less) unstable condition and is favorable (unfavorable) to the strengthening of the convective circulation. The bottom-heavy structure is associated with shallow convection, while the top-heavy structure is usually related to deep convection. This study suggests a hypothesis and a possible linkage for projecting and understanding future circulation change from the current climate: shallow convection will tend to strengthen tropical circulation and enhance upward motion in a future warmer climate.

Climate Model Forecast Experiments for TOGA COARE

2008 ◽  
Vol 136 (3) ◽  
pp. 808-832 ◽  
Author(s):  
J. Boyle ◽  
S. Klein ◽  
G. Zhang ◽  
S. Xie ◽  
X. Wei
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Deep Convection ◽  
Atmospheric Model ◽  
Static Stability ◽  
Geophysical Fluid Dynamics Laboratory ◽  
State Variables ◽  
Tropical Ocean ◽  
Model Version ◽  
Toga Coare

Abstract Short-term (1–10 day) forecasts are made with climate models to assess the parameterizations of the physical processes. The time period for the integrations is that of the intensive observing period (IOP) of the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). The models used are the National Center for Atmospheric Research (NCAR) Community Climate Model, version 3.1 (CAM3.1); CAM3.1 with a modified deep convection parameterization; and the Geophysical Fluid Dynamics Laboratory (GFDL) Atmospheric Model, version 2 (AM2). The models were initialized using the state variables from the 40-yr ECMWF Re-Analysis (ERA-40). The CAM deep convective parameterization fails to demonstrate the sensitivity to the imposed forcing to simulate precipitation patterns associated with the Madden–Julian oscillations (MJOs) present during the period. AM2 and modified CAM3.1 exhibit greater correspondence to the observations at the TOGA COARE site, suggesting that convective parameterizations that have some type of limiter (as do AM2 and the modified CAM3.1) simulate the MJO rainfall with more fidelity than those without. None of the models are able to fully capture the correct phasing of westerly wind bursts with respect to precipitation in the eastward-moving MJO disturbance. Better representation of the diabatic heating and effective static stability profiles is associated with a better MJO simulation. Because the models’ errors in the forecast mode bear a resemblance to the errors in the climate mode in simulating the MJO, the forecasts may allow for a better way to dissect the reasons for model error.

Role of Vertical Structure of Convective Heating in MJO Simulation in NCAR CAM5.3

2017 ◽  
Vol 30 (18) ◽  
pp. 7423-7439 ◽  
Author(s):  
Guyu Cao ◽  
Guang J. Zhang
Keyword(s):  
Vertical Structure ◽  
Climate Models ◽  
Spectral Power ◽  
Deep Convection ◽  
Lower Troposphere ◽  
Global Climate Models ◽  
Convective Heating ◽  
Shallow Convection ◽  
Heating Profile

Abstract Observational studies suggest that the vertical structure of diabatic heating is important to MJO development. In particular, the lack of a top-heavy heating profile was believed to be responsible for poor MJO simulations in global climate models. In this work, the role of the vertical heating profile in MJO simulation is investigated by modifying the convective heating profile to different shapes, from top-heavy heating to bottom cooling, to mimic mesoscale heating in the NCAR Community Atmosphere Model, version 5.3 (CAM5.3). Results suggest that incorporating a mesoscale stratiform heating structure can significantly improve the MJO simulation. By artificially adding stratiform-like heating and cooling in the experiments, many observed features of MJO are reproduced, including clear eastward propagation, a westward-tilted vertical structure of MJO-scale anomalies of dynamic and thermodynamic fields, and strong 20–80-day spectral power. Further analysis shows an abundance of shallow convection ahead of MJO deep convection, confirming the role of shallow convection in preconditioning the atmosphere by moistening the lower troposphere ahead of deep convection during the MJO life cycle. Additional experiments show that lower-level cooling contributes more to improving the MJO simulation. All these features are lacking in the control simulation, suggesting that the mesoscale stratiform heating, especially its lower-level cooling component, is important to MJO simulation.

scholarly journals Sensitivity of a Mediterranean Tropical-Like Cyclone to Physical Parameterizations

Atmosphere ◽  
2018 ◽  
Vol 9 (11) ◽  
pp. 436 ◽  
Author(s):  
Ioannis Pytharoulis ◽  
Stergios Kartsios ◽  
Ioannis Tegoulias ◽  
Haralambos Feidas ◽  
Mario Miglietta ◽  
...  
Keyword(s):  
Surface Layer ◽  
Prediction Models ◽  
Deep Convection ◽  
Weather Prediction ◽  
Boundary Surface ◽  
Shallow Convection ◽  
Roughness Lengths ◽  
Important Challenge ◽  
The One ◽  
Physical Parameterizations

The accurate prediction of Mediterranean tropical-like cyclones, or medicanes, is an important challenge for numerical weather prediction models due to their significant adverse impact on the environment, life, and property. The aim of this study is to investigate the sensitivity of an intense medicane, which formed south of Sicily on 7 November 2014, to the microphysical, cumulus, and boundary/surface layer schemes. The non-hydrostatic Weather Research and Forecasting model (version 3.7.1) is employed. A symmetric cyclone with a deep warm core, corresponding to a medicane, develops in all of the experiments, except for the one with the Thompson microphysics. There is a significant sensitivity of different aspects of the simulated medicane to the physical parameterizations. Its intensity is mainly influenced by the boundary/surface layer scheme, while its track is mainly influenced by the representation of cumulus convection, and its duration is mainly influenced by microphysical parameterization. The modification of the drag coefficient and the roughness lengths of heat and moisture seems to improve its intensity, track, and duration. The parameterization of shallow convection, with explicitly resolved deep convection, results in a weaker medicane with a shorter lifetime. An optimum combination of physical parameterizations in order to simulate all of the characteristics of the medicane does not seem to exist.

scholarly journals Triggering Deep Convection with a Probabilistic Plume Model

2014 ◽  
Vol 71 (11) ◽  
pp. 3881-3901 ◽  
Author(s):  
Fabio D’Andrea ◽  
Pierre Gentine ◽  
Alan K. Betts ◽  
Benjamin R. Lintner
Keyword(s):  
Climate Models ◽  
Proper Time ◽  
Deep Convection ◽  
Potential Temperature ◽  
Specific Humidity ◽  
Cloud Base ◽  
Moist Convection ◽  
Density Currents ◽  
Shallow Convection ◽  
Plume Model

Abstract A model unifying the representation of the planetary boundary layer and dry, shallow, and deep convection, the probabilistic plume model (PPM), is presented. Its capacity to reproduce the triggering of deep convection over land is analyzed in detail. The model accurately reproduces the timing of shallow convection and of deep convection onset over land, which is a major issue in many current general climate models. PPM is based on a distribution of plumes with varying thermodynamic states (potential temperature and specific humidity) induced by surface-layer turbulence. Precipitation is computed by a simple ice microphysics, and with the onset of precipitation, downdrafts are initiated and lateral entrainment of environmental air into updrafts is reduced. The most buoyant updrafts are responsible for the triggering of moist convection, causing the rapid growth of clouds and precipitation. Organization of turbulence in the subcloud layer is induced by unsaturated downdrafts, and the effect of density currents is modeled through a reduction of the lateral entrainment. The reduction of entrainment induces further development from the precipitating congestus phase to full deep cumulonimbus. Model validation is performed by comparing cloud base, cloud-top heights, timing of precipitation, and environmental profiles against cloud-resolving models and large-eddy simulations for two test cases. These comparisons demonstrate that PPM triggers deep convection at the proper time in the diurnal cycle and produces reasonable precipitation. On the other hand, PPM underestimates cloud-top height.

scholarly journals An Analysis of Tropical Ocean Diurnal Warm Layers

2009 ◽  
Vol 22 (13) ◽  
pp. 3629-3646 ◽  
Author(s):  
Hugo Bellenger ◽  
Jean-Philippe Duvel
Keyword(s):  
Time Series ◽  
General Circulation ◽  
Surface Wind ◽  
Equatorial Indian Ocean ◽  
Tropical Climate ◽  
Surface Fluxes ◽  
Environmental Data ◽  
Surface Velocity ◽  
Tropical Ocean ◽  
Early Afternoon

Abstract During periods of light surface wind, a warm stable layer forms at the ocean surface with a maximum sea surface temperature (SST) in the early afternoon. The diurnal SST amplitude (DSA) associated with these diurnal warm layers (DWLs) can reach several degrees and impact the tropical climate variability. This paper first presents an approach to building a daily time series of the DSA over the tropics between 1979 and 2002. The DSA is computed over 2.5° of latitude–longitude regions using a simple DWL model forced by hourly-interpolated surface radiative and turbulent fluxes given by the 40-yr ECMWF Re-Analysis (ERA-40). One advantage of this approach is the homogeneity of the results given by the relative homogeneity of ERA-40. The approach is validated at the global scale using empirical DWL models reported in the literature and the Surface Velocity Program (SVP) drifters of the Marine Environmental Data Service (MEDS). For the SVP dataset, a new technique is introduced to derive the diurnal variation of the temperature from raw measurements. This DWL time series is used to analyze the potential role of DWLs in the variability of the tropical climate. The perturbation of the surface fluxes by DWLs can give a cooling of the ocean mixed layer as large as 2.5 K yr−1 in some tropical regions. On a daily basis, this flux perturbation is often above 10 W m−2 and sometimes exceeds 50 W m−2. DWLs can be organized on regions up to a few thousand kilometers and can persist for more than 5 days. It is shown that strong DWLs develop above the equatorial Indian Ocean during the suppressed phase of the intraseasonal oscillation (ISO). DWLs may trigger large-scale convective events and favor the eastward propagation of the ISO convective perturbation during boreal winter. This study also suggests that the simple approach presented here may be used as a DWL parameterization for atmospheric general circulation models.

Climate Models Permit Convection at Much Coarser Resolutions Than Previously Considered

2020 ◽  
Vol 33 (5) ◽  
pp. 1915-1933 ◽  
Author(s):  
Jesús Vergara-Temprado ◽  
Nikolina Ban ◽  
Davide Panosetti ◽  
Linda Schlemmer ◽  
Christoph Schär
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Deep Convection ◽  
Model Performance ◽  
Shallow Convection ◽  
Grid Spacing ◽  
Radiative Balance ◽  
Model Biases ◽  
Convective Processes ◽  
Model Dynamics

AbstractThe “gray zone” of convection is defined as the range of horizontal grid-space resolutions at which convective processes are partially but not fully resolved explicitly by the model dynamics (typically estimated from a few kilometers to a few hundred meters). The representation of convection at these scales is challenging, as both parameterizing convective processes or relying on the model dynamics to resolve them might cause systematic model biases. Here, a regional climate model over a large European domain is used to study model biases when either using parameterizations of deep and shallow convection or representing convection explicitly. For this purpose, year-long simulations at horizontal resolutions between 50- and 2.2-km grid spacing are performed and evaluated with datasets of precipitation, surface temperature, and top-of-the-atmosphere radiation over Europe. While simulations with parameterized convection seem more favorable than using explicit convection at around 50-km resolution, at higher resolutions (grid spacing ≤ 25 km) models tend to perform similarly or even better for certain model skills when deep convection is turned off. At these finer scales, the representation of deep convection has a larger effect in model performance than changes in resolution when looking at hourly precipitation statistics and the representation of the diurnal cycle, especially over nonorographic regions. The shortwave net radiative balance at the top of the atmosphere is the variable most strongly affected by resolution changes, due to the better representation of cloud dynamical processes at higher resolutions. These results suggest that an explicit representation of convection may be beneficial in representing some aspects of climate over Europe at much coarser resolutions than previously thought, thereby reducing some of the uncertainties derived from parameterizing deep convection.

Sign in / Sign up

Export Citation Format

Share Document