Nonuniqueness in a Single-Column Model for Moist Convection

Abstract We investigate a moist atmospheric column convection model by considering the atmosphere as a single vertical column of air parcels, each of which contains water vapor. The moist convective adjustment of both air and water mass in the column is considered from an (unstable) initial state to a statically stable final configuration of parcels. Two variations of an algorithm based upon swapping neighboring parcels are compared: after swapping, no parcels remain supersaturated. The results of these algorithms are compared directly with those of the adjustment algorithm of Cheng et al., which adjusts an atmospheric column to achieve the global maximum of a relevant cost functional. Two examples are considered: in the first, the algorithms adjust to similar arrangements, showing that the global maximum of the functional is the dynamically preferred state, while in the second, the algorithms adjust to significantly different states. Thus, we identify a nonuniqueness to the solution to the adjustment problem in terms of local and global cost functional maximizers. We then discuss the relevance of this nonuniqueness to numerical prediction in weather and climate models.

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CMIP6 model-based analog forecasting for the seasonal prediction of sea surface temperature in the offshore area of China

Geoscience Letters ◽

10.1186/s40562-021-00179-7 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Weiying Peng ◽

Quanliang Chen ◽

Shijie Zhou ◽

Ping Huang

Keyword(s):

Surface Temperature ◽

Sea Surface Temperature ◽

Climate Models ◽

Global Climate Models ◽

Sea Surface ◽

Seasonal Forecasts ◽

Initial State ◽

Initial Field ◽

Offshore Area ◽

Model Based

AbstractSeasonal forecasts at lead times of 1–12 months for sea surface temperature (SST) anomalies (SSTAs) in the offshore area of China are a considerable challenge for climate prediction in China. Previous research suggests that a model-based analog forecasting (MAF) method based on the simulations of coupled global climate models provide skillful climate forecasts of tropical Indo-Pacific SSTAs. This MAF method selects the model-simulated cases close to the observed initial state as a model-analog ensemble, and then uses the subsequent evolution of the SSTA to generate the forecasts. In this study, the MAF method is applied to the offshore area of China (0°–45°N, 105°–135°E) based on the simulations of 23 models from phase 6 of the Coupled Model Intercomparison Project (CMIP6) for the period 1981–2010. By optimizing the key factors in the MAF method, we suggest that the optimal initial field for the analog criteria should be concentrated in the western North Pacific. The multi-model ensemble of the optimized MAF prediction using these 23 CMIP6 models shows anomaly correlation coefficients exceeding 0.6 at the 3-month lead time, which is much improved relative to previous SST-initialized hindcasts and appears practical for operational forecasting.

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Rethinking convective quasi-equilibrium: observational constraints for stochastic convective schemes in climate models

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2008.0056 ◽

2008 ◽

Vol 366 (1875) ◽

pp. 2579-2602 ◽

Cited By ~ 59

Author(s):

J. David Neelin ◽

Ole Peters ◽

Johnny W.-B Lin ◽

Katrina Hales ◽

Christopher E Holloway

Keyword(s):

Water Vapour ◽

Large Scale ◽

Climate Models ◽

Sensitivity Study ◽

Continuous Phase ◽

Quasi Equilibrium ◽

Moist Convection ◽

Spatial Averaging ◽

Substantial Impact ◽

Long Range Correlations

Convective quasi-equilibrium (QE) has for several decades stood as a key postulate for parametrization of the impacts of moist convection at small scales upon the large-scale flow. Departures from QE have motivated stochastic convective parametrization, which in its early stages may be viewed as a sensitivity study. Introducing plausible stochastic terms to modify the existing convective parametrizations can have substantial impact, but, as for so many aspects of convective parametrization, the results are sensitive to details of the assumed processes. We present observational results aimed at helping to constrain convection schemes, with implications for each of conventional, stochastic or ‘superparametrization’ schemes. The original vision of QE due to Arakawa fares well as a leading approximation, but with a number of updates. Some, like the imperfect connection between the boundary layer and the free troposphere, and the importance of free-tropospheric moisture to buoyancy, are quantitatively important but lie within the framework of ensemble-average convection slaved to the large scale. Observations of critical phenomena associated with a continuous phase transition for precipitation as a function of water vapour and temperature suggest a more substantial revision. While the system's attraction to the critical point is predicted by QE, several fundamental properties of the transition, including high precipitation variance in the critical region, need to be added to the theory. Long-range correlations imply that this variance does not reduce quickly under spatial averaging; scaling associated with this spatial averaging has potential implications for superparametrization. Long tails of the distribution of water vapour create relatively frequent excursions above criticality with associated strong precipitation events.

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The Effect of Explicit Convection on Couplings between Rainfall, Humidity, and Ascent over Africa under Climate Change

Journal of Climate ◽

10.1175/jcli-d-19-0322.1 ◽

2020 ◽

Vol 33 (19) ◽

pp. 8315-8337 ◽

Cited By ~ 2

Author(s):

Lawrence S. Jackson ◽

Declan L. Finney ◽

Elizabeth J. Kendon ◽

John H. Marsham ◽

Douglas J. Parker ◽

...

Keyword(s):

Climate Change ◽

Large Scale ◽

Climate Models ◽

Regional Climate ◽

Hadley Circulation ◽

Moist Convection ◽

Rain Belt ◽

Adaptation To Climate Change ◽

Convective Scale ◽

Mean Climate

AbstractThe Hadley circulation and tropical rain belt are dominant features of African climate. Moist convection provides ascent within the rain belt, but must be parameterized in climate models, limiting predictions. Here, we use a pan-African convection-permitting model (CPM), alongside a parameterized convection model (PCM), to analyze how explicit convection affects the rain belt under climate change. Regarding changes in mean climate, both models project an increase in total column water (TCW), a widespread increase in rainfall, and slowdown of subtropical descent. Regional climate changes are similar for annual mean rainfall but regional changes of ascent typically strengthen less or weaken more in the CPM. Over a land-only meridional transect of the rain belt, the CPM mean rainfall increases less than in the PCM (5% vs 14%) but mean vertical velocity at 500 hPa weakens more (17% vs 10%). These changes mask more fundamental changes in underlying distributions. The decrease in 3-hourly rain frequency and shift from lighter to heavier rainfall are more pronounced in the CPM and accompanied by a shift from weak to strong updrafts with the enhancement of heavy rainfall largely due to these dynamic changes. The CPM has stronger coupling between intense rainfall and higher TCW. This yields a greater increase in rainfall contribution from events with greater TCW, with more rainfall for a given large-scale ascent, and so favors slowing of that ascent. These findings highlight connections between the convective-scale and larger-scale flows and emphasize that limitations of parameterized convection have major implications for planning adaptation to climate change.

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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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A 1D RCE Study of Factors Affecting the Tropical Tropopause Layer and Surface Climate

Journal of Climate ◽

10.1175/jcli-d-18-0778.1 ◽

2019 ◽

Vol 32 (20) ◽

pp. 6769-6782 ◽

Cited By ~ 7

Author(s):

Sally Dacie ◽

Lukas Kluft ◽

Hauke Schmidt ◽

Bjorn Stevens ◽

Stefan A. Buehler ◽

...

Keyword(s):

Water Vapor ◽

Climate Models ◽

Temperature Response ◽

Global Climate Models ◽

Lapse Rate ◽

Tropical Tropopause Layer ◽

Tropical Tropopause ◽

Surface Climate ◽

Ozone Profile ◽

Convective Adjustment

Abstract There are discrepancies between global climate models regarding the evolution of the tropical tropopause layer (TTL) and also whether changes in ozone impact the surface under climate change. We use a 1D clear-sky radiative–convective equilibrium model to determine how a variety of factors can affect the TTL and how they influence surface climate. We develop a new method of convective adjustment, which relaxes the temperature profile toward the moist adiabat and allows for cooling above the level of neutral buoyancy. The TTL temperatures in our model are sensitive to CO2 concentration, ozone profile, the method of convective adjustment, and the upwelling velocity, which is used to calculate a dynamical cooling rate in the stratosphere. Moreover, the temperature response of the TTL to changes in each of the above factors sometimes depends on the others. The surface temperature response to changes in ozone and upwelling at and above the TTL is also strongly amplified by both stratospheric and tropospheric water vapor changes. With all these influencing factors, it is not surprising that global models disagree with regard to TTL structure and evolution and the influence of ozone changes on surface temperatures. On the other hand, the effect of doubling CO2 on the surface, including just radiative, water vapor, and lapse-rate feedbacks, is relatively robust to changes in convection, upwelling, or the applied ozone profile.

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ISMIP6 Future Projections for Antarctica performed using the AWI PISM ice sheet model

10.5194/egusphere-egu2020-16948 ◽

2020 ◽

Author(s):

Thomas Kleiner ◽

Jeremie Schmiedel ◽

Angelika Humbert

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Climate Models ◽

Ice Sheets ◽

Ice Sheet ◽

Ice Shelf ◽

Initial State ◽

Intercomparison Project ◽

Non Local ◽

The Impact

Ice sheets constitute the largest and most uncertain potential source of future sea-level rise. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) brings together a consortium of international ice sheet and climate models to explore the contribution from the Greenland and Antarctic ice sheets to future sea-level rise. We use the Parallel Ice Sheet Model (PISM, pism-docs.org) to carry out spinup and projection simulations for the Antarctic Ice Sheet. Our treatment of the ice-ocean boundary condition previously based on 3D ocean temperatures (initMIP-Antarctica) has been adopted to use the ISMIP6 parameterisation and 3D ocean forcing fields (temperature and salinity) according to the ISMIP6 protocol. In this study, we analyse the impact of the choices made during the model initialisation procedure on the initial state. We present the AWI PISM results of the ISMIP6 projection simulations and investigate the ice sheet response for individual basins. In the analysis, we distinguish between the local and non-local ice shelf basal melt parameterisation.

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A model for moist convection in an ascending atmospheric column

Quarterly Journal of the Royal Meteorological Society ◽

10.1002/qj.3144 ◽

2017 ◽

Vol 143 (708) ◽

pp. 2925-2939 ◽

Cited By ~ 1

Author(s):

B. Cheng ◽

M. J. P. Cullen ◽

J. G. Esler ◽

J. Norbury ◽

M. R. Turner ◽

...

Keyword(s):

Moist Convection ◽

Atmospheric Column

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Evaluation of the CMIP5 models in the aim of regional modelling of the Antarctic surface mass balance

The Cryosphere Discussions ◽

10.5194/tcd-9-3113-2015 ◽

2015 ◽

Vol 9 (3) ◽

pp. 3113-3136 ◽

Cited By ~ 1

Author(s):

C. Agosta ◽

X. Fettweis ◽

R. Datta

Keyword(s):

Mass Balance ◽

Temperature Increase ◽

Climate Models ◽

Regional Climate ◽

Cmip5 Models ◽

Surface Mass Balance ◽

Initial State ◽

Sea Ice Extent ◽

Surface Mass ◽

The Antarctic

Abstract. The Antarctic surface mass balance (SMB) cannot be reliably deduced from global climate models (GCMs), both because their spatial resolution is insufficient and because their physics are not adapted for cold and snow-covered regions. By contrast, regional climate models (RCMs) adapted for polar regions can physically and dynamically downscale surface mass balance components over the ice-sheet using large scale forcing at their boundaries. Polar-oriented RCMs require appropriate GCM fields for forcing because the response of the cryosphere to a warming climate is dependent on its initial state and is not linear with respect to temperature increase. In this context, we evaluate current climate in 41 climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) dataset over Antarctica by focusing on forcing fields which may have the greatest impact on SMB components simulated by RCMs. Our inter-comparison includes 5 reanalyses, among which ERA-Interim reanalysis is chosen as a reference over 1979–2014. Model efficiency is assessed taking into account the multi-decadal variability of the fields over the 1850–1980 period. We show that less than 10 CMIP5 models show reasonable biases compared to ERA-Interim, among which ACCESS1-3 seems to be the most pertinent choice for regional climate modeling over Antarctica, followed by CMCC-CM, MIROC-ESM/MIROC-ESM-CHEM and NorESM1-M. Finally, climate change over the Southern Ocean is much more dependent on the initial state of winter sea-ice extent and on the local feedback between air temperature increase and winter sea-ice extent decrease than on the global warming signal.

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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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Evaluation of Organized Convection Parameterization in Global Climate Models

10.5194/egusphere-egu2020-3758 ◽

2020 ◽

Author(s):

Chih-Chieh Chen ◽

Changhai Liu ◽

Mitch Moncrieff ◽

Yaga Richter

Keyword(s):

Climate Models ◽

Global Climate ◽

Earth System Model ◽

Global Climate Models ◽

System Model ◽

Moist Convection ◽

Earth System ◽

Mesoscale Convective ◽

Convective Organization ◽

Organized Convection

The importance of convective organization on the global circulation has been recognized for a long time, but parameterizations of the associated processes are missing in global climate models. Contemporary convective parameterizations commonly use a convective plume model (or a spectrum of plumes). This is perhaps appropriate for unorganized convection but the assumption of a gap between the small cumulus scale and the large-scale motion fails to recognize mesoscale dynamics manifested in mesoscale convective systems (MCSs) and multi-scale cloud systems associated with the MJO. Organized convection is abundant in environments featuring vertical wind shear, and significantly modulates the life cycle of moist convection, the transport of heat and momentum, and accounts for a large percentage of precipitation in the tropics. Mesoscale convective organization is typically associated with counter-gradient momentum transport, and distinct heating profiles between the convective and stratiform regions.Moncrieff, Liu and Bogenschutz (2017) recently developed a dynamical based parameterization of organized moisture convection, referred to as multiscale coherent structure parameterization (MCSP), for global climate models. A prototype version of MCSP has been implemented in the NCAR Community Earth System Model (CESM) and the Energy Exascale Earth System Model (E3SM), positively affecting the distribution of tropical precipitation, convectively coupled tropical waves, and the Madden-Julian oscillation. We will show the further development of the MCSP and its impact on the simulation of mean precipitation and variability in the two global climate models.

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