scholarly journals A Mass and Energy Conservation Analysis of Drift in the CMIP6 Ensemble

2021 ◽  
Author(s):  
Damien Irving
Keyword(s):  
Climate Models ◽  
Heat Content ◽  
Moisture Flux ◽  
Cmip5 Models ◽  
Energy Budgets ◽  
Freshwater Flux ◽  
Atmospheric Moisture ◽  
State Variables ◽  
Conservation Of Energy ◽  
Ocean Mass

Coupled climate models are prone to ‘drift’ (long-term unforced trends in state variables) due to incomplete spin-up and non-closure of the global mass and energy budgets. Here we assess model drift and the associated conservation of energy, mass and salt in CMIP6 and CMIP5 models. For most models, drift in globally-integrated ocean mass and heat content represents a small but non-negligible fraction of recent historical trends, while drift in atmospheric water vapor is negligible. Model drift tends to be much larger in time-integrated ocean heat and freshwater flux, net top-of-the-atmosphere radiation (netTOA) and moisture flux into the atmosphere (evaporation minus precipitation), indicating a substantial leakage of mass and energy in the simulated climate system. Most models are able to achieve approximate energy budget closure after drift is removed, but ocean mass budget closure eludes a number of models even after de-drifting and none achieve closure of the atmospheric moisture budget. The magnitude of the drift in the CMIP6 ensemble represents an improvement over CMIP5 in some cases (salinity and time-integrated netTOA) but is worse (time-integrated ocean freshwater and atmospheric moisture fluxes) or little changed (ocean heat content, ocean mass and time-integrated ocean heat flux) for others, while closure of the ocean mass and energy budgets after drift removal has improved.

scholarly journals A Mass and Energy Conservation Analysis of Drift in the CMIP6 Ensemble

2020 ◽  
pp. 1-43
Author(s):  
Damien Irving ◽  
Will Hobbs ◽  
John Church ◽  
Jan Zika
Keyword(s):  
Climate Models ◽  
Heat Content ◽  
Moisture Flux ◽  
Cmip5 Models ◽  
Energy Budgets ◽  
Freshwater Flux ◽  
Atmospheric Moisture ◽  
State Variables ◽  
Conservation Of Energy ◽  
Ocean Mass

AbstractCoupled climate models are prone to ‘drift’ (long-term unforced trends in state variables) due to incomplete spin-up and non-closure of the global mass and energy budgets. Here we assess model drift and the associated conservation of energy, mass and salt in CMIP6 and CMIP5 models. For most models, drift in globally-integrated ocean mass and heat content represents a small but non-negligible fraction of recent historical trends, while drift in atmospheric water vapor is negligible. Model drift tends to be much larger in time-integrated ocean heat and freshwater flux, net top-of-the-atmosphere radiation (netTOA) and moisture flux into the atmosphere (evaporation minus precipitation), indicating a substantial leakage of mass and energy in the simulated climate system. Most models are able to achieve approximate energy budget closure after drift is removed, but ocean mass budget closure eludes a number of models even after de-drifting and none achieve closure of the atmospheric moisture budget. The magnitude of the drift in the CMIP6 ensemble represents an improvement over CMIP5 in some cases (salinity and time-integrated netTOA) but is worse (time-integrated ocean freshwater and atmospheric moisture fluxes) or little changed (ocean heat content, ocean mass and time-integrated ocean heat flux) for others, while closure of the ocean mass and energy budgets after drift removal has improved.

Estimating the Thermodynamic and Dynamic Contributions to Hydroclimatic Change over Peninsular Florida

2020 ◽  
Author(s):  
Vasubandhu Misra ◽  
Amit Bhardwaj
Keyword(s):  
Climate Models ◽  
Model Simulation ◽  
Global Climate ◽  
Moisture Flux ◽  
Global Climate Models ◽  
Freshwater Flux ◽  
Late 20Th Century ◽  
Florida Shelf ◽  
Projected Change ◽  
Hydroclimatic Change

AbstractIn this study we examine the thermodynamically and dynamically forced hydroclimatic changes in the four representative seasons over Peninsular Florida (PF) from an unprecedented pair of high resolution regional coupled ocean-atmosphere model simulations conducted at 10km grid spacing for both the atmospheric and the oceanic components forced by one of the global climate models that participated in CMIP5. The model simulation verifies reasonably well with the observations and captures the distinct seasonal cycle of the region. The projected change in the freshwater flux in the mid-21st century (2041-2060) relative to the late 20th century (1986-2005) shows a precipitation deficit in the summer over PF, which is statistically significant. This projected change in freshwater flux over PF is enabled by the strengthening of the anticyclonic North Atlantic Subtropical High Circulation with corresponding changes in divergence of moisture, advection of moisture from changes in the winds and in the change in humidity gradient, and from the change in moisture flux convergence by the transient eddies. These changes suggest that a future warm climate could witness a drier summer over PF at the expense of a wetter West Florida Shelf. The analysis conducted in this study reveals that the changes in atmospheric circulation have a significant impact on the hydroclimate, far more than that implied by the Clausius Clapeyron Equation from changes in temperature.

scholarly journals An Energy Conservation Analysis of Ocean Drift in the CMIP5 Global Coupled Models*

2016 ◽  
Vol 29 (5) ◽  
pp. 1639-1653 ◽  
Author(s):  
Will Hobbs ◽  
Matthew D. Palmer ◽  
Didier Monselesan
Keyword(s):  
Energy Budget ◽  
Climate Model ◽  
Heat Content ◽  
Ocean Model ◽  
Future Climate Change ◽  
Energy Budgets ◽  
State Variables ◽  
Coupled Models ◽  
Significant Disagreement ◽  
Climate Model Simulations

Abstract Climate model simulations of changes to Earth’s energy budget are fundamental to improve understanding of both historical and future climate change. However, coupled models are prone to “drift” (i.e., they contain spurious unforced trends in state variables) due to incomplete spinup or nonclosure of the energy budget. This work assesses the globally integrated energy budgets of 25 models in phase 5 of CMIP (CMIP5). It is shown that for many of the models there is a significant disagreement between ocean heat content changes and net top-of-atmosphere radiation. The disagreement is largely time-constant and independent of forcing scenario. Furthermore, most of the nonconservation seems to occur as a result of energy leaks external to the ocean model realm. After drift correction, the time-varying energy budget is consistent at decadal time scales, and model responses to climate forcing are not sensitive to the magnitude of their drift. This demonstrates that, although drift terms can be significant, model output can be corrected post hoc without biasing results.

scholarly journals Boundary condition and oceanic impacts on the atmospheric water balance in limited area climate model ensembles

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Klaus Goergen ◽  
Stefan Kollet
Keyword(s):  
Boundary Conditions ◽  
Climate Models ◽  
Climate Model ◽  
Regional Climate ◽  
Moisture Flux ◽  
Limited Area ◽  
Atmospheric Moisture ◽  
Atmospheric Water ◽  
Flux Divergence ◽  
Water Budgets

AbstractRegional climate models (RCMs) are indispensable in climate research, albeit often characterized by biased terrestrial precipitation and water budgets. This study identifies excess oceanic evaporation, in conjunction with the RCMs’ boundary conditions, as drivers contributing to these biases in RCMs with forced sea surface temperatures in a CORDEX RCM ensemble over Europe. The RCMs are relaxed to the prescribed lateral boundary conditions originating from a global model, effectively matching the driving model's overall atmospheric moisture flux divergence. As a consequence, excess oceanic evaporation results in positive precipitation biases over land due to forced internal recycling of moisture to maintain the overall flux divergence prescribed by the boundary conditions. This systematic behaviour is shown through an analysis of long-term atmospheric water budgets and atmospheric moisture exchange between oceanic and continental areas in a multi-model ensemble.

Austral Summer Droughts and their Driving Mechanisms in Observations and Present-day Climate Simulations across Malawi

2021 ◽  
Author(s):  
Emmanuel Likoya ◽  
Cathryn Birch ◽  
Sarah Chapman ◽  
Andrew Dougill
Keyword(s):  
Atmospheric Circulation ◽  
Climate Models ◽  
Moisture Flux ◽  
Development Planning ◽  
Global Climate Models ◽  
Cmip5 Models ◽  
Atmospheric Circulation Patterns ◽  
Societal Relevance ◽  
Circulation Patterns ◽  
Moisture Fluxes

<p>The societal relevance of droughts in Africa underscores the need for improved understanding of the atmospheric processes that drive them. This study examined drought characteristics across Malawi, and the associated atmospheric circulation patterns, in observations, reanalysis and global climate models. Droughts were identified using the Standardised Precipitation and Evapotranspiration Index (SPEI) for the period 1965 to 2018. Atmospheric circulation patterns during droughts were examined and the main moisture fluxes into Malawi were identified. Despite differences in the frequency, and events being asynchronous at times, droughts exhibited characteristics that were statistically similar between northern and southern Malawi. Droughts in both regions were associated with anomalous circulation that typically worked to diminish moisture advection and thus convection. Differences in the structure of the anomalies were indicative of differences in mechanisms associated with droughts in the north and south of Malawi. Three main moisture flux pathways were identified, and categorized as northeasterly, southeasterly, and northwesterly, each with a unique correlation structure with precipitation and global SSTs. Positive and negative biases of varying magnitudes were noted for drought and rainfall characteristics across the range of CMIP5 models. Such biases can be attributed to biases in moisture fluxes whose variability was found to be a key driver of summer precipitation variability across Malawi. Despite biases in moisture fluxes and their influence on precipitation biases, the majority of models exhibited moisture flux-precipitation correlations consistent with observations and reanalysis. Results from the study highlight the extent to which climate models are reliable in simulating droughts and therefore of value in developing narratives of climate variability essential for long-term development planning.</p>

scholarly journals Antarctic moisture flux and net accumulation from global atmospheric analyses

1995 ◽  
Vol 21 ◽  
pp. 149-156 ◽  
Author(s):  
W.F. Budd ◽  
P. A. Reid ◽  
L.J. Minty
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Moisture Flux ◽  
Global Climate Models ◽  
Atmospheric Moisture ◽  
Prediction Scheme ◽  
Moisture Fluxes ◽  
New Generation ◽  
The Antarctic

Previous attempts to derive the Antarctic surface net accumulation distribution from atmospheric-moisture fluxes, in reasonable agreement with the observed distribution, have encountered many difficulties. The present analysis uses the Australian Bureau of Meteorology Global Atmospheric Assimilation and Prediction Scheme (GASP), which has been operational since 1989, to derive the net air-mass and moisture fluxes over the Antarctic. It is shown that the annual mean net surface accumulation closely resembles the glaciologically observed distribution and provides a physical basis for the observed pattern, through the moisture transports. The variations with latitude and elevation and through the annual cycle are also well reproduced. Although some mass-closure errors still exist, they are expected to become insignificant with the new generation of improved analysis schemes. Consequently the atmospheric analyses can provide a sound basis for both assessing the performance of global climate models in simulating Antarctic accumulation rates and monitoring long-term changes which may occur with global warming.

scholarly journals Antarctic moisture flux and net accumulation from global atmospheric analyses

1995 ◽  
Vol 21 ◽  
pp. 149-156 ◽  
Author(s):  
W.F. Budd ◽  
P. A. Reid ◽  
L.J. Minty
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Moisture Flux ◽  
Global Climate Models ◽  
Atmospheric Moisture ◽  
Prediction Scheme ◽  
Moisture Fluxes ◽  
New Generation ◽  
The Antarctic

Previous attempts to derive the Antarctic surface net accumulation distribution from atmospheric-moisture fluxes, in reasonable agreement with the observed distribution, have encountered many difficulties. The present analysis uses the Australian Bureau of Meteorology Global Atmospheric Assimilation and Prediction Scheme (GASP), which has been operational since 1989, to derive the net air-mass and moisture fluxes over the Antarctic. It is shown that the annual mean net surface accumulation closely resembles the glaciologically observed distribution and provides a physical basis for the observed pattern, through the moisture transports. The variations with latitude and elevation and through the annual cycle are also well reproduced. Although some mass-closure errors still exist, they are expected to become insignificant with the new generation of improved analysis schemes. Consequently the atmospheric analyses can provide a sound basis for both assessing the performance of global climate models in simulating Antarctic accumulation rates and monitoring long-term changes which may occur with global warming.

Effects of mesoscale ocean flows on multidecadal climate variability

2020 ◽  
Author(s):  
André Jüling ◽  
Anna von der Heydt ◽  
Henk Dijkstra
Keyword(s):  
Climate Variability ◽  
Surface Temperature ◽  
Climate Models ◽  
Heat Content ◽  
Global Climate Models ◽  
Cmip5 Models ◽  
Multidecadal Variability ◽  
Global Mean Surface Temperature ◽  
Ocean Flows ◽  
Global Mean

<div> <div>Climate variability on decadal to multidecadal time scales appears to be organized in pronounced patterns with clear expressions in sea surface temperature, such as the Pacific Multidecadal Variability and the Atlantic Multidecadal Variability. These patterns are now well studied both in observations and in global climate models and are important in the attribution of climate change. Results in CMIP5 models have indicated large biases in these patterns with consequences for ocean heat storage variability and eventually the global mean surface temperature.</div> <div>We use two multi-century Community Earth System Model simulations at coarse (1°) and fine (0.1°) ocean model horizontal grid spacing and study the effect of the representation of mesoscale ocean flows on major patterns of multidecadal variability. We find that resolving mesoscale ocean flows both improves the characteristics of the modes of variability with respect to observations and increases the amplitude of the heat content variability in the individual ocean basins. However, the effect on the global mean surface temperature is relatively minor.</div> </div>

scholarly journals A Coupled Dynamic Index for ENSO Periodicity

2018 ◽  
Vol 31 (6) ◽  
pp. 2361-2376 ◽  
Author(s):  
Bo Lu ◽  
Fei-Fei Jin ◽  
Hong-Li Ren
Keyword(s):  
Climate Models ◽  
Southern Oscillation ◽  
Heat Content ◽  
Dominant Mode ◽  
Cmip5 Models ◽  
Model Simulations ◽  
Dynamic Index ◽  
F Factor ◽  
Time Space ◽  
Recent Climate

El Niño–Southern Oscillation (ENSO) is the most active interannual climatic mode, with great global impacts. The state-of-the-art climate models can simulate this dominant mode variability to a large extent. Nevertheless, some of ENSO’s fundamental time–space characteristics still have a large spread in the simulations across the array of recent climate models. For example, the large biases of ENSO periodicity still exist among model simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5). Based on the recharge oscillator framework, a coupled dynamic index for ENSO periodicity is proposed in this study, referred to as the Wyrtki index, in parallel to the Bjerknes index for ENSO instability. The Wyrtki index provides an approximate dynamic measure for ENSO linear periodicity. It has two main contribution terms: the thermocline and zonal advective feedbacks (or F factor) multiplied by the efficiency factor B of discharging–recharging of the equatorial heat content driven by ENSO wind stress anomalies. It is demonstrated that the diversity of simulated ENSO periodicity in CMIP5 models results from the biases in mean state and several key parameters that control ENSO dynamics. A larger F factor would result in a shorter ENSO period [e.g., BCC_CSM1.1(m)], whereas a smaller B factor would lead to a longer ENSO period (e.g., HadGEM2-ES). The Wyrtki index serves as a useful tool for a quantitative assessment of the sources for ENSO periodicity in reanalysis data and its biases in CMIP5 model simulations.

scholarly journals A seamless approach to understanding and predicting Arctic sea ice in Met Office modelling systems

2015 ◽  
Vol 373 (2045) ◽  
pp. 20140161 ◽  
Author(s):  
Helene T. Hewitt ◽  
Jeff K. Ridley ◽  
Ann B. Keen ◽  
Alex E. West ◽  
K. Andrew Peterson ◽  
...  
Keyword(s):  
Sea Ice ◽  
Seasonal Cycle ◽  
Climate Models ◽  
Early Summer ◽  
Arctic Sea Ice ◽  
Heat Fluxes ◽  
Cmip5 Models ◽  
Energy Budgets ◽  
Arctic Sea ◽  
Use Of Models

Recent CMIP5 models predict large losses of summer Arctic sea ice, with only mitigation scenarios showing sustainable summer ice. Sea ice is inherently part of the climate system, and heat fluxes affecting sea ice can be small residuals of much larger air–sea fluxes. We discuss analysis of energy budgets in the Met Office climate models which point to the importance of early summer processes (such as clouds and meltponds) in determining both the seasonal cycle and the trend in ice decline. We give examples from Met Office modelling systems to illustrate how the seamless use of models for forecasting on time scales from short range to decadal might help to unlock the drivers of high latitude biases in climate models.

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