Tropical convection regimes in climate models: evaluation with satellite observations

Abstract. High-quality observations are powerful tools for the evaluation of climate models towards improvement and reduction of uncertainty. Particularly at low latitudes, the most uncertain aspect lies in the representation of moist convection and interaction with dynamics, where rising motion is tied to deep convection and sinking motion to dry regimes. Since humidity is closely coupled with temperature feedbacks in the tropical troposphere, a proper representation of this region is essential. Here we demonstrate the evaluation of atmospheric climate models with satellite-based observations from Global Positioning System (GPS) radio occultation (RO), which feature high vertical resolution and accuracy in the troposphere to lower stratosphere. We focus on the representation of the vertical atmospheric structure in tropical convection regimes, defined by high updraft velocity over warm surfaces, and investigate atmospheric temperature and humidity profiles. Results reveal that some models do not fully capture convection regions, particularly over land, and only partly represent strong vertical wind classes. Models show large biases in tropical mean temperature of more than 4 K in the tropopause region and the lower stratosphere. Reasonable agreement with observations is given in mean specific humidity in the lower to mid-troposphere. In moist convection regions, models tend to underestimate moisture by 10 to 40 % over oceans, whereas in dry downdraft regions they overestimate moisture by 100 %. Our findings provide evidence that RO observations are a unique source of information, with a range of further atmospheric variables to be exploited, for the evaluation and advancement of next-generation climate models.

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Tropical convection regimes in climate models: evaluation with satellite observations

10.5194/acp-2017-669 ◽

2017 ◽

Author(s):

Andrea K. Steiner ◽

Bettina C. Lackner ◽

Mark A. Ringer

Keyword(s):

Climate Models ◽

Lower Stratosphere ◽

Deep Convection ◽

Atmospheric Temperature ◽

Tropical Convection ◽

Specific Humidity ◽

Moist Convection ◽

Tropopause Region ◽

Tropical Troposphere ◽

Unique Source

Abstract. High quality observations are powerful tools for the evaluation of climate models towards improvement and reduction of uncertainty. Particularly at low latitudes, the most uncertain aspect lies in the representation of moist convection and interaction with dynamics, where rising motion is tied to deep convection and sinking motion to dry regimes. Since humidity is closely coupled with temperature feedbacks in the tropical troposphere a proper representation of this region is essential. Here we demonstrate the evaluation of atmospheric climate models with satellite-based observations from Global Positioning System (GPS) radio occultation (RO), which feature high vertical resolution and accuracy in the troposphere to lower stratosphere. We focus on the representation of the vertical atmospheric structure in tropical convection regimes, defined by high updraft velocity over warm surfaces, and investigate atmospheric temperature and humidity profiles. Results reveal that some models do not fully capture convection regions, particularly over land, and only partly represent high updraft or downdraft velocities. Models show large biases in tropical mean temperature of more than 4 K in the tropopause region and the lower stratosphere. Reasonable agreement with observations is given in mean specific humidity in the lower to mid-troposphere. In moist convection regions, models tend to underestimate moisture by 10 % to 30 % over oceans whereas in dry downdraft regions they overestimate moisture by 100 %. Our findings provide evidence that RO observations are a unique source of information, with a range of further atmospheric variables to be exploited, for the evaluation and advancement of next generation climate models.

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Triggering Deep Convection with a Probabilistic Plume Model

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-13-0340.1 ◽

2014 ◽

Vol 71 (11) ◽

pp. 3881-3901 ◽

Cited By ~ 19

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.

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Role of Convection–circulation Coupling in the Propagation Mechanism of the Madden–Julian Oscillation over the Maritime Continent in Climate Models

10.21203/rs.3.rs-343249/v1 ◽

2021 ◽

Author(s):

Yi-Chi Wang ◽

Wan-Ling Tseng ◽

Huang-Hsiung Hsu

Keyword(s):

Climate Models ◽

Environmental Changes ◽

Deep Convection ◽

Ocean Model ◽

Cumulus Parameterization ◽

Propagation Mechanism ◽

Madden Julian Oscillation ◽

Moist Convection ◽

Maritime Continent

Abstract This study investigates the role of convection–circulation coupling on the simulated eastward propagation of the Madden–Julian Oscillation (MJO) over the Maritime Continent (MC). Experiments are conducted with the European Centre Hamburg Model Version 5 (ECHAM5) coupled with the one-column ocean model – Snow-Ice-Thermocline (SIT) and two different cumulus schemes, Nordeng (E5SIT-Nord) and Tiedtke (E5SIT-Tied). During the early phase of MJO composites, the E5SIT-Nord simulation reveals stronger intraseasonal anomalies in the apparent heat source (Q1) over the convective center, however, the E5SIT-Tied produces a stronger background Q1, suggesting that deep convection prevails over the MC but does not couple with the MJO circulation. Similarly, in the E5SIT-Tied simulation, in-column moisture is kept mostly by local deep convection over the MC, which is in contrast to the well-correlated relationship between moisture anomaly and MJO circulation in E5SIT-Nord. A case study based on an observational MJO reveals similar biases concerning of convection–circulation coupling emerges within a few days of simulations. The E5SIT-Tied simulation produces weaker heating at the convective center of the MJO than the E5SIT-Nord a few days after model initiation, resulting weaker subsidence to the east and less favorable for propagation. The present findings highlight the instantaneous responses of cumulus parameterization schemes to MJO-related environmental changes can further affect intraseasonal variability through altering convection–circulation coupling over the MC. Physical schemes of moist convection are essential to realistically represent this coupling and thereby improve the simulation of the eastward propagation of the MJO.

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Updraft dynamics and microphysics: on the added value of the cumulus thermal reference frame in simulations of aerosol-deep convection interactions

10.5194/acp-2021-586 ◽

2021 ◽

Author(s):

Daniel Hernandez-Deckers ◽

Toshihisa Matsui ◽

Ann M. Fridlind

Keyword(s):

Reference Frames ◽

Climate Models ◽

Deep Convection ◽

Building Blocks ◽

Quantitative Information ◽

Added Value ◽

Cumulus Convection ◽

Moist Convection ◽

Microphysical Processes

Abstract. One fundamental question about atmospheric moist convection processes that remains debated is whether or under what conditions a relevant variability in background aerosol concentrations may have a significant dynamical impact on convective clouds and their associated precipitation. Furthermore, current climate models must parameterize both the microphysical and the cumulus convection processes, but this is usually implemented separately, whereas in nature there is a strong coupling between them. As a first step to improve our understanding of these two problems, we investigate how aerosol concentrations modify key properties of updrafts in eight large-eddy permitting regional simulations of a case study of scattered convection over Houston, Texas, in which convection is explicitly simulated and microphysical processes are parameterized. Dynamical and liquid-phase microphysical responses are investigated using two different reference frames: static cloudy-updraft grid cells versus tracked cumulus thermals. In both frameworks we observe the expected microphysical responses to higher aerosol concentrations, such as higher cloud number concentrations and lower rain number concentrations. In terms of the dynamical responses, both frameworks indicate weak impacts of varying aerosol concentrations relative to the noise between simulations over the observationally derived range of aerosol variability for this case study. On the other hand, results suggest that analysis of thermals can provide a better pathway to sample the most relevant convective processes. For instance, vertical velocity from thermals is significantly higher at upper levels than when sampled from cloudy-updraft grid points, and several microphysical variables have higher average values in the cumulus thermal framework than in the cloudy-updraft framework. In addition, the thermal analysis is seen to add rich quantitative information about the rates and covariability of microphysical processes spatially and throughout tracked thermal lifecycles, which can serve as a stronger foundation for improving subgrid-scale parameterizations. These results suggest that cumulus thermals are more realistic dynamical building blocks of cumulus convection, acting as natural cloud chambers for microphysical processes.

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Relationship between surface and tropospheric water vapor variation on interannual timescale: A revisit

10.5194/egusphere-egu2020-22688 ◽

2020 ◽

Author(s):

Mengmiao Yang ◽

De-Zheng Sun ◽

Guang J. Zhang

Keyword(s):

Water Vapor ◽

Climate Models ◽

Deep Convection ◽

Specific Humidity ◽

Cmip5 Models ◽

Moisture Regime ◽

Strongly Correlated ◽

Strongly Coupled ◽

Significant Difference ◽

The Tropics

It is an old question whether tropospheric water vapor at different levels changes consistently in response to the enhanced greenhouse gas in the atmosphere. Earlier studies using older versions of climate models and available data revealed a significant difference between models and observations. Water vapor changes in the interior of the tropical troposphere have been found to be more strongly coupled to changes at the surface in climate models than in observations. We reexamine this issue using four leading CMIP5 models (CCSM4, HadGEM2-A, GFDL-CM3 and MPI-ESM-MR) and more updated observational datasets (ERA-Interim and NCEP reanalysis).&#160;Focusing on the Tropics, we have calculated the&#160;correlations between interannual&#160;variation&#160;of specific humidity in all levels of the troposphere with that at the surface. It is found that the previously noted biases in the strength of the coupling between water vapor changes in the interior of the troposphere and those at the surface still exist in the updated models&#8212;the change in the tropical averaged tropospheric water vapor is more strongly correlated with the change in the surface, especially in the middle troposphere. It is argued that the vertical profile of water vapor correlations in observations is more consistent with the &#8220;hot tower&#8221; concept for tropical convections. Zonal mean correlation results and those from the moisture regime sorting method are consistent with each other, both of which indicate the role of deep convection as a mechanism to couple the middle tropospheric water vapor and that in the surface and that an inaccurate representation of deep convection as a possible cause for the discrepancies between models and observations in the coupling between middle tropospheric water vapor and those at the surface.

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A Transilient Matrix for Moist Convection

Journal of the Atmospheric Sciences ◽

10.1175/2011jas3712.1 ◽

2011 ◽

Vol 68 (9) ◽

pp. 2009-2025 ◽

Cited By ~ 20

Author(s):

David M. Romps ◽

Zhiming Kuang

Keyword(s):

Potential Energy ◽

Deep Convection ◽

Convective Available Potential Energy ◽

Free Troposphere ◽

Moist Convection ◽

Initial Height ◽

Available Potential Energy ◽

Tropical Troposphere ◽

Nonlocal Transport

Abstract A method is introduced for diagnosing a transilient matrix for moist convection. This transilient matrix quantifies the nonlocal transport of air by convective eddies: for every height z, it gives the distribution of starting heights z′ for the eddies that arrive at z. In a cloud-resolving simulation of deep convection, the transilient matrix shows that two-thirds of the subcloud air convecting into the free troposphere originates from within 100 m of the surface. This finding clarifies which initial height to use when calculating convective available potential energy from soundings of the tropical troposphere.

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A Mechanism of Tropical Convection Inferred from Observed Variability in the Moist Static Energy Budget

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-14-0015.1 ◽

2014 ◽

Vol 71 (10) ◽

pp. 3747-3766 ◽

Cited By ~ 24

Author(s):

Hirohiko Masunaga ◽

Tristan S. L’Ecuyer

Keyword(s):

Energy Budget ◽

Large Scale ◽

Deep Convection ◽

Vertical Motion ◽

Tropical Convection ◽

Radiative Heating ◽

Moist Convection ◽

Baroclinic Mode ◽

Moist Static Energy ◽

Static Energy

Abstract Temporal variability in the moist static energy (MSE) budget is studied with measurements from a combination of different satellites including the Tropical Rainfall Measuring Mission (TRMM) and A-Train platforms. A composite time series before and after the development of moist convection is obtained from the observations to delineate the evolution of MSE and moisture convergences and, in their combination, gross moist stability (GMS). A new algorithm is then applied to estimate large-scale vertical motion from energy budget constraints through vertical-mode decomposition into first and second baroclinic modes and a background shallow mode. The findings are indicative of a possible mechanism of tropical convection. A gradual destabilization is brought about by the MSE convergence intrinsic to the positive second baroclinic mode (congestus mode) that increasingly counteracts a weak MSE divergence in the background state. GMS is driven to nearly zero as the first baroclinic mode begins to intensify, accelerating the growth of vigorous large-scale updrafts and deep convection. As the convective burst peaks, the positive second mode switches to the negative mode (stratiform mode) and introduces an abrupt rise in MSE divergence that likely discourages further maintenance of deep convection. The first mode quickly dissipates and GMS increases away from zero, eventually returning to the background shallow-mode state. A notable caveat to this scenario is that GMS serves as a more reliable metric when defined with a radiative heating rate included to offset MSE convergence.

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Tropical deep convection and its impact on composition in global and mesoscale models - Part 1: Meteorology and comparison with observations.

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-19469-2010 ◽

2010 ◽

Vol 10 (8) ◽

pp. 19469-19514 ◽

Cited By ~ 2

Author(s):

M. R. Russo ◽

V. Marécal ◽

C. R. Hoyle ◽

J. Arteta ◽

C. Chemel ◽

...

Keyword(s):

Water Vapour ◽

Climate Models ◽

Lower Stratosphere ◽

Numerical Models ◽

Convective Transport ◽

Tropical Convection ◽

Tropical Regions ◽

Upper Troposphere ◽

Surface Precipitation ◽

Spatial And Temporal Scales

Abstract. Tropical convection is a very important atmospheric process acting on the water cycle, radiative budget of the atmosphere and air composition of the upper troposphere and lower stratosphere (UTLS), and it affects a broad range of spatial and temporal scales. The fast vertical transport in convective plumes can efficiently redistribute water vapour and pollutants up to the Tropical Tropopause Layer (TTL), and therefore affect the composition of the lower stratosphere. Chemistry Climate Models and Chemistry Transport Models are routinely used to study chemical processes in the atmosphere. In these models convection and convective transport of tracers are parameterised, and due to the interplay of chemical and dynamical processes, it has proven difficult to evaluate the convective transport of chemical species by comparison with observed chemical fields. In this work we investigate different characteristics of tropical convection by using convective proxies from many independent observational datasets (including surface precipitation rates, cloud top pressure and OLR). We use observations to analyse the seasonal cycle and geographical preferences of convection, and its impact on water vapour. Using highly temporally resolved cloud top data we calculate the frequency distribution of high clouds in three tropical regions. The observational data is used as a benchmark for a number of numerical models, with a view to assess the ability of models to reproduce the seasonality, preferential location and vertical extent of tropical convection. Finally we discuss the implications of our findings on modelling the composition of the upper troposphere and lower stratosphere.

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When the trigger of deep convection gets tricky in idealized climate simulations

10.5194/egusphere-egu21-9497 ◽

2021 ◽

Author(s):

Dominic Matte ◽

Jens H. Christensen ◽

Henrik Fedderson ◽

Rasmus A. Pederson ◽

Henrik Vedel ◽

...

Keyword(s):

Climate Models ◽

Initial Conditions ◽

Flash Flood ◽

Deep Convection ◽

Regional Climate ◽

Lapse Rate ◽

Moist Convection ◽

Extreme Precipitation Events ◽

Synoptic Conditions ◽

Deep Moist Convection

On the evening on July 2, 2011 a severe cloud burst occurred in the Copenhagen area. During the late afternoon deep moist convection developed over nearby Sk&#229;ne (the southernmost part of Sweden) in an airstream from east-northeast. In the early evening the DMC passed over &#216;resund to Copenhagen, where it created a severe flash flood. Between 90 and 135 mm of precipitation in less than 2 hours was recorded ooding cellars, streets, and key roads. The deluge caused 6 billion Danish kroner in damage. Although that such extreme events are rare, the impacts on society is important and should be understood under a warmer climate. Although regional climate models have recently reached the convection permitting resolution, reproducing such events is still challenging.Several studies suggest that extreme precipitations should increase under a future warmer climate using transient simulation or a pseudo-warming approach. It is still unclear how such event would behave under warmer or colder synoptic conditions. Using a forecast-ensemble method, but keeping a climate perspective, this study assesses the risk rising from such an event under otherwise almost identical, but warmer or colder conditions. With this set-up, we find that the development of the system that resulted in observed downpour exhibit quite a sensitivity to the initial conditions and contrary to a linear thinking, the risk of flooding is decreasing as the climate warms due to the inhibition of the CAPE by the additional lapse-rate anomalies used in this study. We therefore propose that the PGW method should be used with caution and that extreme precipitation events also in transient simulations of future climates need to be studied in detailed to address the limitations to models ability to produce those most extreme and by nature inherently rare events.

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Towards European-Scale Convection-Resolving Climate Simulations

10.5194/gmd-2016-119 ◽

2016 ◽

Cited By ~ 4

Author(s):

David Leutwyler ◽

Oliver Fuhrer ◽

Xavier Lapillonne ◽

Daniel Lüthi ◽

Christoph Schär

Keyword(s):

Graphics Processing Units ◽

Climate Models ◽

Climate Model ◽

Deep Convection ◽

Moist Convection ◽

Cold Pools ◽

Cosmo Model ◽

Climate Simulations ◽

Graphics Processing ◽

Horizontal Grid

Abstract. The representation of moist convection in climate models represents a major challenge, due to the small scales involved. Using horizontal grid spacings of O(1km), convection-resolving weather and climate models allow to explicitly resolve deep convection. However, due to their extremely demanding computational requirements, they have so far been limited to short simulations and/or small computational domains. Innovations in supercomputing have led to new hybrid node designs, mixing conventional multicore CPUs and accelerators such as graphics processing units (GPUs). One of the first atmospheric models that has been fully ported to these architectures is the COSMO model. Here we demonstrate the convection-resolving COSMO model on continental scales using a version of the model capable of using GPU accelerators. The verification of a week-long simulation containing winter storm Kyrill shows that, for this case, convection-parameterizing simulations and convection-resolving simulations agree well. Furthermore we demonstrate the applicability of the approach to longer simulations by conducting a three-month long simulation of the summer season 2006. Its results corroborate the findings found on smaller domains such as more credible representation of the diurnal cycle of precipitation in convection-resolving models and a tendency to produce more intensive hourly precipitation events. Both simulations also show how the approach allows for the representation of interactions between synoptic-scale and meso-scale atmospheric circulations at scales ranging from 1000 to 10 km. This includes the formation of sharp cold frontal structures, convection embedded in fronts and small eddies, or the formation and organization of propagating cold pools. Finally we assess the performance gain from using heterogeneous hardware equipped with GPUs with respect to multi-core hardware. With the COSMO model, we now use a climate model that has all the necessary modules required for real-case convection-resolving climate simulations on GPUs.

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