scholarly journals A Weather-Pattern-Based Evaluation of the Performance of CMIP5 Models over Mexico

Climate ◽  
2020 ◽  
Vol 8 (1) ◽  
pp. 5 ◽  
Author(s):  
Yanet Díaz-Esteban ◽  
Graciela B. Raga ◽  
Oscar Onoe Díaz Rodríguez
Keyword(s):  
Sea Level ◽  
Climate Models ◽  
Weather Type ◽  
Specific Humidity ◽  
Cmip5 Models ◽  
Model Errors ◽  
Sea Level Pressure ◽  
Low Level ◽  
Level Pressure ◽  
Synoptic Conditions

The fifth phase of the Coupled Model Inter-Comparison Project (CMIP5) is frequently used to force regional climate models for dynamic downscaling and projections, which decision makers in turn use for future plans in different sectors. It is, therefore, highly important to assess their performance in order to use them as reliable tools. A weather-type approach for the evaluation of the performance of CMIP5 models is employed in this study, with the objective of providing insight into model errors under a set of distinct synoptic conditions and circulation types associated with the rainy season over Mexico and Central America. The Self-Organizing Maps algorithm is used to identify the main weather regimes (constructed from sea level pressure, specific humidity, and low-level winds at a daily time-scale), which are then evaluated against reanalysis. The results show that model performance depends on the weather type in all of the variables except for sea level pressure, which confirms the usefulness of this approach. The models simulate better the humidity patterns that show weak deviations from the climatological norm. In addition, the wind pattern representing the Caribbean Low Level Jet is well reproduced by all the models. The results show the capacity of this methodology for determining the extent to which climate models represent the main circulation patterns that characterize the climate and local weather in Mexico.

scholarly journals Simulation and Interpretation of the Genesis of Tropical Storm Gert (2005) as Part of the NASA Tropical Cloud Systems and Processes Experiment

2010 ◽  
Vol 67 (4) ◽  
pp. 999-1025 ◽  
Author(s):  
Scott A. Braun ◽  
Michael T. Montgomery ◽  
Kevin J. Mallen ◽  
Paul D. Reasor
Keyword(s):  
Sea Level ◽  
Tropical Storm ◽  
Sea Level Pressure ◽  
Cloud Systems ◽  
Low Level ◽  
Level Pressure ◽  
Stratiform Region ◽  
Stratiform Precipitation ◽  
Precipitation Processes ◽  
The Mean

Abstract Several hypotheses have been put forward for the mechanisms of generation of surface circulation associated with tropical cyclones. This paper examines high-resolution simulations of Tropical Storm Gert (2005), which formed in the Gulf of Mexico during NASA’s Tropical Cloud Systems and Processes Experiment, to investigate the development of low-level circulation and its relationship to the precipitation evolution. Two simulations are examined: one that better matches available observations but underpredicts the storm’s minimum sea level pressure and a second one that somewhat overintensifies the storm but provides a set of simulations that encapsulates the overall genesis and development characteristics of the observed storm. The roles of convective and stratiform precipitation processes within the mesoscale precipitation systems that formed Gert are discussed. During 21–25 July, two episodes of convective system development occurred. In each, precipitation system evolution was characterized by intense and deep convective upward motions followed by increasing stratiform-type vertical motions (upper-level ascent, low-level descent). Potential vorticity (PV) in convective regions was strongest at low levels while stratiform-region PV was strongest at midlevels, suggesting that convective processes acted to spin up lower levels prior to the spinup of middle levels by stratiform processes. Intense vortical hot towers (VHTs) were prominent features of the low-level cyclonic vorticity field. The most prominent PV anomalies persisted more than 6 h and were often associated with localized minima in the sea level pressure field. A gradual aggregation of the cyclonic PV occurred as existing VHTs near the center continually merged with new VHTs, gradually increasing the mean vorticity near the center. Nearly concurrently with this VHT-induced development, stratiform precipitation processes strongly enhanced the mean inflow and convergence at middle levels, rapidly increasing the midlevel vorticity. However, the stratiform vertical motion profile is such that while it increases midlevel vorticity, it decreases vorticity near the surface as a result of low-level divergence. Consequently, the results suggest that while stratiform precipitation regions may significantly increase cyclonic circulation at midlevels, convective vortex enhancement at low to midlevels is likely necessary for genesis.

scholarly journals What Surface Observations Are Important for Separating the Influences of Anthropogenic Aerosols from Other Forcings?

2016 ◽  
Vol 29 (11) ◽  
pp. 4165-4184 ◽  
Author(s):  
Xiaoqin Yan ◽  
Timothy DelSole ◽  
Michael K. Tippett
Keyword(s):  
Spatial Structure ◽  
Surface Temperature ◽  
Sea Level ◽  
Climate Models ◽  
Accurate Estimate ◽  
Forced Response ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol ◽  
Sea Level Pressure ◽  
Level Pressure

Abstract This paper shows that joint temperature–precipitation information over a global domain provides a more accurate estimate of aerosol forced responses in climate models than does any other combination of temperature, precipitation, or sea level pressure. This fact is demonstrated using a new quantity called potential detectability, which measures the extent to which a forced response can be detected in a model. In particular, this measure can be evaluated independently of observations and therefore permits efficient exploration of a large number of variable combinations before performing optimal fingerprinting on observations. This paper also shows that the response to anthropogenic aerosol forcing can be separated from that of other forcings using only spatial structure alone, leaving the time variation of the response to be inferred from data, thereby demonstrating that temporal information is not necessary for detection. The spatial structure of the forced response is derived by maximizing the signal-to-noise ratio. For single variables, the north–south hemispheric gradient and equator-to-pole latitudinal gradient are important spatial structures for detecting anthropogenic aerosols in some models but not all. Sea level pressure is not an independent detection variable because it is derived partly from surface temperature. In no case does sea level pressure significantly enhance potential detectability beyond that already possible using surface temperature. Including seasonal or land–sea contrast information does not significantly enhance detectability of anthropogenic aerosol responses relative to annual means over global domains.

scholarly journals Changes in atmospheric variability in a glacial climate and the impacts on proxy data: a model intercomparison

2009 ◽  
Vol 5 (3) ◽  
pp. 489-502 ◽  
Author(s):  
F. S. R. Pausata ◽  
C. Li ◽  
J. J. Wettstein ◽  
K. H. Nisancioglu ◽  
D. S. Battisti
Keyword(s):  
Sea Level ◽  
North Atlantic ◽  
Climate Models ◽  
Atmospheric Variability ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
The North ◽  
Surface Climate ◽  
Leading Mode ◽  
The North Atlantic Oscillation

Abstract. Using four different climate models, we investigate sea level pressure variability in the extratropical North Atlantic in the preindustrial climate (1750 AD) and at the Last Glacial Maximum (LGM, 21 kyrs before present) in order to understand how changes in atmospheric circulation can affect signals recorded in climate proxies. In general, the models exhibit a significant reduction in interannual variance of sea level pressure at the LGM compared to pre-industrial simulations and this reduction is concentrated in winter. For the preindustrial climate, all models feature a similar leading mode of sea level pressure variability that resembles the leading mode of variability in the instrumental record: the North Atlantic Oscillation (NAO). In contrast, the leading mode of sea level pressure variability at the LGM is model dependent, but in each model different from that in the preindustrial climate. In each model, the leading (NAO-like) mode of variability explains a smaller fraction of the variance and also less absolute variance at the LGM than in the preindustrial climate. The models show that the relationship between atmospheric variability and surface climate (temperature and precipitation) variability change in different climates. Results are model-specific, but indicate that proxy signals at the LGM may be misinterpreted if changes in the spatial pattern and seasonality of surface climate variability are not taken into account.

scholarly journals Projected Significant Increase in the Number of Extreme Extratropical Cyclones in the Southern Hemisphere

2017 ◽  
Vol 30 (13) ◽  
pp. 4915-4935 ◽  
Author(s):  
Edmund K. M. Chang
Keyword(s):  
Sea Level ◽  
Southern Hemisphere ◽  
Cmip5 Models ◽  
General Interest ◽  
Extratropical Cyclones ◽  
The South ◽  
Sea Level Pressure ◽  
Near Surface ◽  
Level Pressure ◽  
South Indian

Extratropical cyclones are responsible for much of the extreme weather in the midlatitudes; thus, how these cyclones may change under increasing greenhouse gas forcing is of much general interest. Previous studies have suggested a poleward shift in the location of these cyclones, but how the intensity may change remains uncertain, especially in terms of maximum wind speed. In this study, projected changes in extreme cyclones in the Southern Hemisphere, based on 26 models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5), are presented. Multiple definitions of extreme cyclones have been examined, including intensity exceeding constant thresholds of sea level pressure perturbations, 850-hPa vorticity, and 850-hPa winds, as well as variable thresholds corresponding to a top-5 or top-1 cyclone per winter month in these three parameters and the near-surface winds. Results presented show that CMIP5 models project a significant increase in the frequency of extreme cyclones in all four seasons regardless of the definition, with over 88% of the models projecting an increase. Spatial patterns of increase are also consistent, with the largest increase projected between 45° and 60°S, extending from the South Atlantic across the south Indian Ocean into the Pacific. The projected increases in cyclone statistics are consistent with those in Eulerian statistics, such as sea level pressure (SLP) variance. However, while the projected increase in SLP variance can be linked to increase in the mean available potential energy (MAPE), the increases in cyclone statistics are not well correlated with those in MAPE.

scholarly journals Simulations of Arctic Temperature and Pressure by Global Coupled Models

2007 ◽  
Vol 20 (4) ◽  
pp. 609-632 ◽  
Author(s):  
William L. Chapman ◽  
John E. Walsh
Keyword(s):  
Sea Level ◽  
Climate Models ◽  
Barents Sea ◽  
Global Climate ◽  
Global Climate Models ◽  
First Century ◽  
The Arctic ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
Twenty First Century

Abstract Simulations of Arctic surface air temperature and sea level pressure by 14 global climate models used in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change are synthesized in an analysis of biases and trends. Simulated composite GCM surface air temperatures for 1981–2000 are generally 1°–2°C colder than corresponding observations with the exception of a cold bias maximum of 6°–8°C in the Barents Sea. The Barents Sea bias, most prominent in winter and spring, occurs in 12 of the 14 GCMs and corresponds to a region of oversimulated sea ice. All models project a twenty-first-century warming that is largest in the autumn and winter, although the rates of the projected warming vary considerably among the models. The across-model and across-scenario uncertainties in the projected temperatures are comparable through the first half of the twenty-first century, but increases in variability associated with the choice of scenario begin to outpace increases in across-model variability by about the year 2070. By the end of the twenty-first century, the cross-scenario variability is about 50% greater than the across-model variability. The biases of sea level pressure are smaller than in the previous generation of global climate models, although the models still show a positive bias of sea level pressure in the Eurasian sector of the Arctic Ocean, surrounded by an area of negative pressure biases. This bias is consistent with an inability of the North Atlantic storm track to penetrate the Eurasian portion of the Arctic Ocean. The changes of sea level pressure projected for the twenty-first century are negative over essentially the entire Arctic. The most significant decreases of pressure are projected for the Bering Strait region, primarily in autumn and winter.

scholarly journals Spatial Distribution And Synoptic Conditions Of Snow Accumulation And Snow Ablation In The West Siberian Plain

2015 ◽  
Vol 34 (3) ◽  
pp. 5-15 ◽  
Author(s):  
Ewa Bednorz ◽  
Joanna Wibig
Keyword(s):  
Sea Level ◽  
Cold Season ◽  
Snow Accumulation ◽  
West Siberian Plain ◽  
The West ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
The North ◽  
Synoptic Conditions ◽  
Air Circulation

Abstract The mean duration of snow coverage in the West Siberian Plain is approximately eight months in the north to about five months in the south. While the period of intense snow melting is short (one or two months between March and May), snow accumulation persists for most of the cold season. Snow accumulation is associated with negative anomalies of sea level pressure, which means increased cyclonal activity and weaker than normal Siberian High. Much lower anomalies of sea level pressure occur during snow ablation. This suggests smaller influence of air circulation on snow cover reduction in spring.

scholarly journals Summertime circumglobal Rossby waves in climate models: Small biases in upper-level circulation create substantial biases in surface imprint

2021 ◽  
Author(s):  
Fei Luo ◽  
Frank Selten ◽  
Kathrin Wehrli ◽  
Kai Kornhuber ◽  
Philippe Le Sager ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Sea Level ◽  
General Circulation ◽  
Climate Models ◽  
Rossby Waves ◽  
Boreal Summer ◽  
Sea Level Pressure ◽  
Near Surface ◽  
Level Pressure ◽  
Upper Level

Abstract. In boreal summer, circumglobal Rossby waves can promote stagnating weather systems that favor extreme events like heatwaves or droughts. Recent work highlighted the risks associated with amplified Rossby wavenumber 5 and 7 in triggering simultaneous warm anomalies in specific agricultural breadbaskets in the Northern Hemisphere. These type of wave patterns thus pose potential risks for food production, as well as human health, and other impacts. The representation of such summertime wave events and their surface imprints in general circulation models (GCMs) has not been  systematically analyzed. Here we validate three state-of-the-art global climate models (EC-Earth, CESM, and MIROC), quantify their biases and provide insights into the underlying physical reasons for the biases. To do so, the ExtremeX  experiments output data were used, which are (1) historic simulations (1979–2015/2016) of a freely running atmosphere with prescribed ocean, and experiments that additionally nudge toward the observed (2) upper-level horizontal winds in the atmosphere, (3) soil moisture conditions, or (4) both. The nudged experiments are used to trace the sources of the model biases to either the large-scale atmospheric circulation or surface feedback processes. We show that while the wave position and magnitude is represented well compared to ERA5 reanalysis data. During high amplitudes (> 1.5 s.d.) wave-5 and wave- 7 events, the imprint on surface variables temperature, precipitation and sea level pressure is substantially underestimated: typically, by a factor of 1.5 in correlation and normalized standard deviations (n.s.d.) for near-surface temperature and mean sea level pressure. As for the precipitation, it’s still a factor of 1.5 for n.s.d. but 2 for correlation. The correlations and n.s.d. for surface variables do not improve if only the soil moisture is prescribed, but considerably increased when the upper-level atmosphere circulation is nudged. The underestimation factors are corrected almost entirely. When applying both soil moisture prescription and the nudging of upper-level atmosphere, both the correlation and n.s.d. values are quite similar to  only atmosphere component is nudged experiments. Hence, the near-surface biases can be substantially improved when nudging the upper-level circulation providing evidence that relatively small biases in the models’ representation of the upper-level waves can strongly affect associated temperature and rainfall anomalies.

scholarly journals Analysis of synoptic conditions for tornadic days over Western Greece

2014 ◽  
Vol 2 (3) ◽  
pp. 2215-2243
Author(s):  
P. T. Nastos ◽  
I. T. Matsangouras
Keyword(s):  
Sea Level ◽  
Sea Level Pressure ◽  
Vulnerable Area ◽  
Atmospheric Research ◽  
Level Pressure ◽  
Synoptic Conditions ◽  
Environmental Prediction ◽  
Western Greece

Abstract. Tornadoes have been reported in Greece during the last decades and recent studies have given evidence that west Greece is a vulnerable area for tornadoes, waterspouts and funnel clouds to occur. In this study, the composite means and anomalies of synoptic conditions for tornadic events (tornadoes, waterspouts and funnel clouds) over west Greece are analyzed and discussed. The daily composite means of synoptic conditions were based on National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP/NCAR) reanalysis datasets, for the period 12 August 1953 to 31 December 2012. The daily composite anomalies were calculated with respect to 30 years climatology (1981–2010) of the synoptic conditions. The analysis was carried out in terms of seasonal and monthly variability of composite means and anomalies of synoptic conditions for specific isobaric levels of 500, 700, 850, 925 hPa and the sea level pressure (SLP). In addition, an analysis and discussion about the dynamic Lifted Index from NCEP/NCAR Reanalysis datasets is presented.

A multivariate assessment of climate change projections over South America using CMIP5 models

2020 ◽  
Author(s):  
Paul Loikith ◽  
Valerie Thaler ◽  
Luana Albertani Pampuch ◽  
C. Roberto Mechoso ◽  
Armineh Barkhordarian ◽  
...  
Keyword(s):  
Climate Change ◽  
South America ◽  
Sea Level ◽  
Storm Track ◽  
Northeastern Brazil ◽  
Cmip5 Models ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
Poleward Shift ◽  
Model Agreement

<p>A multivariate assessment of climate model projections over South America from the CMIP5 archive is presented. Change in near-surface temperature, precipitation, evapotranspiration, integrated water vapor transport (IVT), sea level pressure, and wind at multiple pressure levels is quantified across the multi-model suite and an assessment of model-to-model agreement on projected change performed. All models project warming by the mid- and late-21<sup>st</sup> century throughout the continent, with the highest magnitude projected over tropical regions. The CMIP5 models are in strong agreement that precipitation will decrease in all seasons over portions of Patagonia, especially along the northern portions of the current-climate mid-latitude storm track. This is consistent with a robustly projected poleward shift of the Pacific extratropical high and mid-latitude storm track indicated by a systematic increase in sea level pressure and decrease in westerly wind over Patagonia. Decreased precipitation for the months of September, October, and November is also projected, with strong model agreement, over portions of northern and northeastern Brazil, coincident with decreases in sea level pressure and increases in evapotranspiration. IVT is broadly projected to decrease over southern South America, coincident with the projected poleward shift of the mid-latitude storm track indicators, with increases projected in the vicinity of the South Atlantic Convergence Zone in austral spring and summer. Further decomposition of the thermodynamic and dynamic components to this change in IVT indicate that the projected decreases in the mid-latitudes are primarily driven by changes in circulation (i.e. dynamic) while the sub-tropical and tropical changes have a predominantly thermodynamic origin. Results provide a comprehensive picture of climate change across South America and highlight where projections should be interpreted with the most confidence.</p>

scholarly journals Changes in atmospheric variability in a glacial climate and the impacts on proxy data: a model intercomparison

2009 ◽  
Vol 5 (2) ◽  
pp. 911-936 ◽  
Author(s):  
F. S. R. Pausata ◽  
C. Li ◽  
J. J. Wettstein ◽  
K. H. Nisancioglu ◽  
D. S. Battisti
Keyword(s):  
Sea Level ◽  
North Atlantic ◽  
Climate Models ◽  
Atmospheric Variability ◽  
Proxy Data ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
The North ◽  
Temperature And Precipitation ◽  
Leading Mode

Abstract. We investigate sea level pressure variability in the extratropical North Atlantic in the preindustrial climate (1750 A.D.) and at the Last Glacial Maximum (LGM, 21 kyr before present) using four climate models. In general, the models exhibit a significant reduction in interannual variance of sea level pressure during the LGM compared to pre-industrial simulations and this reduction is concentrated in winter. For the preindustrial climate, all the models feature a similar leading mode (EOF) of sea level pressure variability that is also similar to the leading mode of variability in the instrumental record: the North Atlantic Oscillation (NAO). In contrast, the leading mode of sea level pressure variability during the LGM is model dependent, but in each model different from that in the preindustrial climate. In each model, the leading (NAO-like) mode of variability explains a smaller fraction of the variance and also less absolute variance in the LGM than in the preindustrial. The leading (NAO-like) mode of sea level pressure variability is shifted southward in the LGM simulations relative to the preindustrial simulations. Finally, we correlate the leading mode of sea level pressure variability with surface temperature and precipitation within each model and for the two time periods. In the preindustrial climate, the leading mode of sea level pressure variability is similar from model to model and the temperature and precipitation correlation patterns are also similar. In contrast, since the models find different dominant modes of sea level pressure variability for the LGM climate, they also disagree on the associated patterns of temperature and precipitation variability. Assuming stationarity of the relationship between surface climate and the leading mode of sea level pressure variability could lead to a misinterpretation of signals recorded in proxy data.

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