scholarly journals The Resolution Sensitivity of Northern Hemisphere Blocking in Four 25-km Atmospheric Global Circulation Models

2017 ◽  
Vol 30 (1) ◽  
pp. 337-358 ◽  
Author(s):  
Reinhard Schiemann ◽  
Marie-Estelle Demory ◽  
Len C. Shaffrey ◽  
Jane Strachan ◽  
Pier Luigi Vidale ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Horizontal Resolution ◽  
Model Ensemble ◽  
Grid Spacing ◽  
Atmospheric Blocking ◽  
Global Circulation ◽  
Global Circulation Models ◽  
Northern European ◽  
The Mean ◽  
Mean State

The aim of this study is to investigate if the representation of Northern Hemisphere blocking is sensitive to resolution in current-generation atmospheric global circulation models (AGCMs). An evaluation is conducted of how well atmospheric blocking is represented in four AGCMs whose horizontal resolution is increased from a grid spacing of more than 100 km to about 25 km. It is shown that Euro-Atlantic blocking is simulated overall more credibly at higher resolution (i.e., in better agreement with a 50-yr reference blocking climatology created from the reanalyses ERA-40 and ERA-Interim). The improvement seen with resolution depends on the season and to some extent on the model considered. Euro-Atlantic blocking is simulated more realistically at higher resolution in winter, spring, and autumn, and robustly so across the model ensemble. The improvement in spring is larger than that in winter and autumn. Summer blocking is found to be better simulated at higher resolution by one model only, with little change seen in the other three models. The representation of Pacific blocking is not found to systematically depend on resolution. Despite the improvements seen with resolution, the 25-km models still exhibit large biases in Euro-Atlantic blocking. For example, three of the four 25-km models underestimate winter northern European blocking frequency by about one-third. The resolution sensitivity and biases in the simulated blocking are shown to be in part associated with the mean-state biases in the models’ midlatitude circulation.

scholarly journals MJO Simulation Diagnostics

2009 ◽  
Vol 22 (11) ◽  
pp. 3006-3030 ◽  
Keyword(s):  
Model Performance ◽  
Diagnostic Techniques ◽  
Life Cycles ◽  
Global Circulation ◽  
Orthogonal Function ◽  
Global Circulation Models ◽  
Wide Range ◽  
Weather And Climate ◽  
The Mean

Abstract The Madden–Julian oscillation (MJO) interacts with and influences a wide range of weather and climate phenomena (e.g., monsoons, ENSO, tropical storms, midlatitude weather), and represents an important, and as yet unexploited, source of predictability at the subseasonal time scale. Despite the important role of the MJO in climate and weather systems, current global circulation models (GCMs) exhibit considerable shortcomings in representing this phenomenon. These shortcomings have been documented in a number of multimodel comparison studies over the last decade. However, diagnosis of model performance has been challenging, and model progress has been difficult to track, because of the lack of a coherent and standardized set of MJO diagnostics. One of the chief objectives of the U.S. Climate Variability and Predictability (CLIVAR) MJO Working Group is the development of observation-based diagnostics for objectively evaluating global model simulations of the MJO in a consistent framework. Motivation for this activity is reviewed, and the intent and justification for a set of diagnostics is provided, along with specification for their calculation, and illustrations of their application. The diagnostics range from relatively simple analyses of variance and correlation to more sophisticated space–time spectral and empirical orthogonal function analyses. These diagnostic techniques are used to detect MJO signals, to construct composite life cycles, to identify associations of MJO activity with the mean state, and to describe interannual variability of the MJO.

Does ocean resolution affect the rate of AMOC weakening?

2020 ◽  
Author(s):  
Helene Hewitt ◽  
Laura Jackson ◽  
Malcolm Roberts ◽  
Dorotea Iovino ◽  
Torben Koenigk ◽  
...  
Keyword(s):  
Deep Water ◽  
Horizontal Resolution ◽  
Meridional Overturning Circulation ◽  
Subpolar Gyre ◽  
Deep Water Formation ◽  
North Atlantic Current ◽  
The North ◽  
Water Formation ◽  
The Mean ◽  
Mean State

<p>We examine the weakening of the Atlantic Meridional Overturning Circulation (AMOC) in response to increasing CO<sub>2</sub> at different horizontal resolutions in HadGEM3-GC3.1 and in a small ensemble of models with differing resolutions. There is a strong influence of the ocean mean state on the AMOC weakening: models with a more saline western subpolar gyre have a greater formation of deep water there. This makes the AMOC more susceptible to weakening from an increase in CO<sub>2</sub> since weakening ocean heat transports weaken the contrast between ocean and atmospheric temperatures and hence weaken the buoyancy loss. In models with a greater proportion of deep water formation further north (in the Greenland-Iceland-Norwegian basin), deep-water formation can be maintained by shifting further north to where there is a greater ocean-atmosphere temperature contrast.</p><p>We show that ocean horizontal resolution can have an impact on the mean state, and hence AMOC weakening. In the models examined, those with higher resolutions tend to have a more westerly path of the North Atlantic Current and hence greater impact of the warm, saline subtropical Atlantic waters on the western subpolar gyre. This results in greater dense water formation in the western subpolar gyre. Although there is some improvement of the higher resolution models over the lower resolution models in terms of the mean state, both still have biases and it is not clear which biases are the most important for influencing the AMOC strength and response to increasing CO<sub>2</sub>.</p><p> </p>

scholarly journals An Explanation for the Sensitivity of the Mean State of the Community Atmosphere Model to Horizontal Resolution on Aquaplanets

2017 ◽  
Vol 30 (13) ◽  
pp. 4781-4797 ◽  
Author(s):  
Adam R. Herrington ◽  
Kevin A. Reed
Keyword(s):  
Moisture Transport ◽  
General Circulation ◽  
Large Scale ◽  
General Circulation Models ◽  
Horizontal Resolution ◽  
Hadley Cell ◽  
Community Atmosphere Model ◽  
The Mean ◽  
Atmosphere Model ◽  
Mean State

The sensitivity of the mean state of the Community Atmosphere Model to horizontal resolutions typical of present-day general circulation models is investigated in an aquaplanet configuration. Nonconvergence of the mean state is characterized by a progressive drying of the atmosphere and large reductions in cloud coverage with increasing resolution. Analyses of energy and moisture budgets indicate that these trends are balanced by variations in moisture transport by the resolved circulation, and a reduction in activity of the convection scheme. In contrast, the large-scale precipitation rate increases with resolution, which is approximately balanced by greater advection of dry static energy associated with more active resolved vertical motion in the ascent region of the Hadley cell. An explanation for the sensitivity of the mean state to horizontal resolution is proposed, based on linear Boussinesq theory. The authors hypothesize that an increase in horizontal resolution in the model leads to a reduction in horizontal scale of the diabatic forcing arising from the column physics, facilitating finescale flow and faster resolved convective updrafts within the dynamical core, and steering the coupled system toward a new mean state. This hypothesis attempts to explain the underlying mechanism driving the variations in moisture transport observed in the simulations.

scholarly journals Deterministic methods for prediction of tropical cyclone tracks

MAUSAM ◽  
2021 ◽  
Vol 48 (2) ◽  
pp. 257-272
Author(s):  
U.C. MOHANTY ◽  
AKHILESH GUPTA
Keyword(s):  
Tropical Cyclone ◽  
Weather Prediction ◽  
Horizontal Resolution ◽  
Limited Area ◽  
Deterministic Models ◽  
Global Circulation ◽  
Global Circulation Models ◽  
Structure And Motion ◽  
Cyclone Tracks ◽  
Tropical Cyclone Tracks

ABSTRACT. The paper presents a state-of-art review of different objective techniques available for tropical cyclone track prediction. A brief description of current theories of tropical cyclone motion is given. Deterministic models with statistical and dynamical methods have been discussed. Recent advances in the understanding of cyclone structure and motion aspects have led to improved prediction of tropical cyclones. There has been considerable progress in the field of prediction by dynamical methods. High resolution Limited Area Models (LAM) as well as Global Circulation Models (GCM) are now being used extensively by most of the leading operational numerical weather prediction (NWP) centres in the world The major achievements towards improvement of such models have come from improved horizontal resolution of the models, inclusion of physical processes, use of synthetic and other non-conventional data in the data assimilation schemes and nudging method for initial matching of analysed cyclone centres with corresponding observations. A brief description of further improvement in deterministic approach for prediction of tropical cyclone tracks is outlined.  

scholarly journals AMM15: a new high-resolution NEMO configuration for operational simulation of the European north-west shelf

2018 ◽  
Vol 11 (2) ◽  
pp. 681-696 ◽  
Author(s):  
Jennifer A. Graham ◽  
Enda O'Dea ◽  
Jason Holt ◽  
Jeff Polton ◽  
Helene T. Hewitt ◽  
...  
Keyword(s):  
High Resolution ◽  
Horizontal Resolution ◽  
Bias Reduction ◽  
Small Scale ◽  
Operational System ◽  
North West ◽  
The North ◽  
European North ◽  
The Mean ◽  
Mean State

Abstract. This paper describes the next-generation ocean forecast model for the European north-west shelf, which will become the basis of operational forecasts in 2018. This new system will provide a step change in resolution and therefore our ability to represent small-scale processes. The new model has a resolution of 1.5 km compared with a grid spacing of 7 km in the current operational system. AMM15 (Atlantic Margin Model, 1.5 km) is introduced as a new regional configuration of NEMO v3.6. Here we describe the technical details behind this configuration, with modifications appropriate for the new high-resolution domain. Results from a 30-year non-assimilative run using the AMM15 domain demonstrate the ability of this model to represent the mean state and variability of the region.Overall, there is an improvement in the representation of the mean state across the region, suggesting similar improvements may be seen in the future operational system. However, the reduction in seasonal bias is greater off-shelf than on-shelf. In the North Sea, biases are largely unchanged. Since there has been no change to the vertical resolution or parameterization schemes, performance improvements are not expected in regions where stratification is dominated by vertical processes rather than advection. This highlights the fact that increased horizontal resolution will not lead to domain-wide improvements. Further work is needed to target bias reduction across the north-west shelf region.

scholarly journals AMM15: A new high resolution NEMO configuration for operational simulation of the European North West Shelf

2017 ◽  
Author(s):  
Jennifer A. Graham ◽  
Enda O’Dea ◽  
Jason Holt ◽  
Jeff Polton ◽  
Helene T. Hewitt ◽  
...  
Keyword(s):  
High Resolution ◽  
Horizontal Resolution ◽  
Bias Reduction ◽  
Small Scale ◽  
Operational System ◽  
North West ◽  
The North ◽  
European North ◽  
The Mean ◽  
Mean State

Abstract. This paper describes the next generation ocean forecast model for the European North West Shelf, which will become the basis of operational forecasts in 2018. This new system will provide a step change in resolution, and therefore our ability to represent small scale processes. The new model has a resolution of 1.5 km, compared with a grid spacing of 7 km in the current operational system. AMM15 (Atlantic Margin Model, 1.5 km) is introduced as a new regional configuration of NEMO v3.6. Here we describe the technical details behind this configuration, with modifications appropriate for the new high resolution domain. Results from a 30 year non-assimilative run, using the AMM15 domain, demonstrate the ability of this model to represent the mean state and variability of the region. Overall, there is an improvement in the representation of the mean state across the region, suggesting similar improvements may be seen in the future operational system. However, the reduction in seasonal bias is greater off-shelf than on-shelf. In the North Sea, biases are largely unchanged. Since there has been no change to the vertical resolution or parameterisation schemes, performance improvements are not expected in regions where stratification is dominated by vertical processes, rather than advection. This highlights the fact that increased horizontal resolution will not lead to domain-wide improvements. Further work is needed to target bias reduction across the North West Shelf region.

scholarly journals Southern Hemisphere Jet Variability in the IPSL GCM at Varying Resolutions

2012 ◽  
Vol 69 (12) ◽  
pp. 3788-3799 ◽  
Author(s):  
Ara Arakelian ◽  
Francis Codron
Keyword(s):  
Southern Hemisphere ◽  
Intraseasonal Variability ◽  
Co2 Concentration ◽  
Southern Annular Mode ◽  
Horizontal Resolution ◽  
Dominant Mode ◽  
The Mean ◽  
Jet Variability ◽  
The Relationship ◽  
Mean State

Abstract Fluctuations of the Southern Hemisphere eddy-driven jet are studied in a suite of experiments with the Laboratoire de Météorologie Dynamique, version 4 (LMDZ4) atmospheric GCM with varying horizontal resolution, in coupled mode and with imposed SSTs. The focus is on the relationship between changes in the mean state brought by increasing resolution, and the intraseasonal variability and response to increasing CO2 concentration. In summer, the mean jet latitude moves poleward when the resolution increases in latitude, converging toward the observed one. Most measures of the jet dynamics, such as skewness of the distribution or persistence time scale of jet movements, exhibit a simple dependence on the mean jet latitude and also converge to the observed values. In winter, the improvement of the mean-state biases with resolution is more limited. In both seasons, the relationship between the dominant mode of variability—the southern annular mode (SAM)—and the mean state remains the same as in observations, except in the most biased winter simulation. The jet fluctuations—latitude shifts or splitting—just occur around a different mean position. Both the model biases and the response to increasing CO2 project strongly onto the SAM structure. No systematic relation between the amplitude of the response and characteristics of the control simulation was found, possibly due to changing dynamics or impacts of the physical parameterizations with different resolutions.

scholarly journals Increased water deficit decreases Douglas fir growth throughout western US forests

2016 ◽  
Vol 113 (34) ◽  
pp. 9557-9562 ◽  
Author(s):  
Christina M. Restaino ◽  
David L. Peterson ◽  
Jeremy Littell
Keyword(s):  
Tree Mortality ◽  
Vapor Pressure Deficit ◽  
Douglas Fir ◽  
Evaporative Demand ◽  
Global Circulation ◽  
Global Circulation Models ◽  
Western Us ◽  
The Mean ◽  
Related Stress ◽  
Global Carbon

Changes in tree growth rates can affect tree mortality and forest feedbacks to the global carbon cycle. As air temperature increases, evaporative demand also increases, increasing effective drought in forest ecosystems. Using a spatially comprehensive network of Douglas fir (Pseudotsuga menziesii) chronologies from 122 locations that represent distinct climate environments in the western United States, we show that increased temperature decreases growth via vapor pressure deficit (VPD) across all latitudes. Using an ensemble of global circulation models, we project an increase in both the mean VPD associated with the lowest growth extremes and the probability of exceeding these VPD values. As temperature continues to increase in future decades, we can expect deficit-related stress to increase and consequently Douglas fir growth to decrease throughout its US range.

Mean-state dependence of future tropical-Atlantic sector climate projections

2020 ◽  
Author(s):  
Wonsun Park ◽  
Mojib Latif ◽  
Arielle Stela Imbol Nkwinkwa Njouodo
Keyword(s):  
Global Warming ◽  
Climate Model ◽  
Horizontal Resolution ◽  
Tropical Pacific ◽  
Climate Projections ◽  
Tropical Atlantic ◽  
Atlantic Sector ◽  
Sst Bias ◽  
The Mean ◽  
Mean State

<p>Mean state and internal variability in the tropics are crucially linked to air-sea interactions. State-of-the-art climate models exhibit long-standing problems not only in simulating tropical mean climate, such as too cold sea surface temperature (SST) over the central tropical Pacific and too warm SST over the eastern tropical Pacific and Atlantic, but also with respect to seasonal and longer variability. These biases question the credibility of future climate projections with the models, and it has not been shown to date whether or how such SST biases affect the projections. Here we focus on the tropical Atlantic (TA) and investigate how the mean state influences climate projections over the region.</p><p>We use two versions of the Kiel Climate Model (KCM) in global warming simulations, in which only atmosphere model resolution differs: one version carries ECHAM5 with a horizontal resolution of T42 (~2.8°) and 31 vertical levels, and the other ECHAM5 with a horizontal resolution of T255 (~0.47°) and 62 levels. Although only the atmospheric resolutions differ, the two KCM versions exhibit very different mean states over the tropical TA, with the higher-resolution version, among others, featuring much reduced warm SST bias over the eastern basin.</p><p>The response to increasing atmospheric carbon dioxide levels is found to be sensitive to the mean state. The model employing high atmospheric resolution and featuring a small SST bias projects an eastward-amplified SST warming over the TA, consistent with the pattern of interannual SST variability simulated under present-day conditions and in line with the observed SST trends since the mid-20<sup>th</sup> century. The model employing low-resolution and exhibiting a large SST bias projects more uniform SST change. Atmospheric changes also vastly differ among the two model versions.</p><p>Analysis of models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) support the KCM’s results: models with small SST bias project stronger warming over the eastern TA, while models with large SST bias either project uniform warming across the equator or largest warming in the west. This study suggests that reducing model bias may enhance global warming projections over the TA sector.</p>

scholarly journals Uncertainty of simulated groundwater recharge at different global warming levels: A global-scale multi-model ensemble study

2020 ◽  
Author(s):  
Robert Reinecke ◽  
Hannes Müller Schmied ◽  
Tim Trautmann ◽  
Peter Burek ◽  
Martina Flörke ◽  
...  
Keyword(s):  
Global Warming ◽  
Groundwater Recharge ◽  
Global Scale ◽  
Model Ensemble ◽  
Uncertainty Range ◽  
Groundwater Availability ◽  
Global Circulation ◽  
Global Circulation Models ◽  
Groundwater Systems ◽  
Simulated Groundwater

Abstract. Billions of people rely on groundwater as an accessible source for drinking water and irrigation, especially in times of drought. Its importance will likely increase with a changing climate. It is still unclear, however, how climate change will impact groundwater systems globally and thus the availability of this vital resource. This study investigates uncertainties in groundwater recharge projections using a multi-model ensemble of eight global hydrological models (GHMs) that are driven by the bias-adjusted output of four global circulation models (GCMs). Preindustrial and current groundwater recharge values are compared with recharge for different global warming (GW) levels as a result of three representative concentration pathways (RCPs). Results suggest that the uncertainty range is extensive, and projections with confidence can only be made for specific regions of the world. In some regions, reversals of groundwater recharge trends can be observed with global warming. On average, a consistent median increase of groundwater recharge in northern Europe of 19 % and a decrease of 10 % in the Amazon at 3 °C GW compared to preindustrial levels are simulated. In the Mediterranean, a 2 °C GW leads to a reduction of GWR of 38 %. Because most GHMs do not include CO2 driven vegetation processes, we investigate how, including the effect of evolving CO2 concentrations into the calculation of future groundwater recharge impacts the results. In some regions, the inclusion of these processes leads to differences in groundwater recharge changes of up to 100 mm year−1. Overall, models that include CO2 driven vegetation processes simulate less severe decreases of groundwater recharge and in some regions even increases instead of decreases. In regions where GCMs predict decreases in precipitation, and groundwater availability is most important, the model agreement among GHMs with dynamic vegetation is lowest in contrast to GHMs without, which show a high agreement.

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