Power-Law Persistence in the Atmosphere: An Ideal Test Bed for Climate Models

2004 ◽  
Author(s):  
Armin Bunde ◽  
Jan Eichner
Keyword(s):  
Power Law ◽  
Climate Models ◽  
Rare Events ◽  
Global Climate ◽  
Temperature Fluctuations ◽  
Global Climate Models ◽  
Test Bed ◽  
Short Term ◽  
Weather Changes

We review recent results on the appearance of long-term persistence in climatic records and their relevance for the evaluation of global climate models and rare events. The persistence can be characterized, for example, by the correlation C(s) of temperature variations separated by s days. We show that, contrary to previous expectations, C(s) decays for large s as a power law, C(s) ~ s<sup>- γ</sup>. For continental stations, the exponent γ is always close to 0.7, while for stations on islands γ ≌ 0.4. In contrast to the temperature fluctuations, the fluctuations of the rainfall usually cannot be characterized by long-term power-law correlations but rather by pronounced short-term correlations. The universal persistence law for the temperature fluctuations on continental stations represents an ideal (and uncomfortable) test-bed for the state-of-the-art global climate models and allows us to evaluate their performance. In addition, the presence of long-term correlations leads to a noval approach for evaluating the statistics of rare events. The persistence of weather states on short terms is a well-known phenomenon: a warm day is more likely to be followed by a warm day than by a cold day and vice versa. The trivial forecast that the weather of tomorrow is the same as the weather of today was, in previous times, often used as a "minimum skill" forecast for assessing the usefulness of short-term weather forecasts. The typical time scale for weather changes is about one week, a time period which corresponds to the average duration of so-called "general weather regimes" or "Grosswetterlagen," so this type of short-term persistence usually stops after about one week. On larger scales, other types of persistence occur, one of them is related to circulation patterns associated with blocking [5]. A blocking situation occurs when a very stable high-pressure system is established over a particular region and remains in place for several weeks. As a result, the weather in the region of the high remains fairly persistent throughout this period. Furthermore, transient low-pressure systems are deflected around the blocking high so that the region downstream of the high experiences a larger than usual number of storms.

scholarly journals Global climatology and trends in convective environments from ERA5 and rawinsonde data

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Mateusz Taszarek ◽  
John T. Allen ◽  
Mattia Marchio ◽  
Harold E. Brooks
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Global Climate ◽  
Convective Available Potential Energy ◽  
Global Climate Models ◽  
Convective Precipitation ◽  
The Past ◽  
The Tropics ◽  
Rawinsonde Data

AbstractGlobally, thunderstorms are responsible for a significant fraction of rainfall, and in the mid-latitudes often produce extreme weather, including large hail, tornadoes and damaging winds. Despite this importance, how the global frequency of thunderstorms and their accompanying hazards has changed over the past 4 decades remains unclear. Large-scale diagnostics applied to global climate models have suggested that the frequency of thunderstorms and their intensity is likely to increase in the future. Here, we show that according to ERA5 convective available potential energy (CAPE) and convective precipitation (CP) have decreased over the tropics and subtropics with simultaneous increases in 0–6 km wind shear (BS06). Conversely, rawinsonde observations paint a different picture across the mid-latitudes with increasing CAPE and significant decreases to BS06. Differing trends and disagreement between ERA5 and rawinsondes observed over some regions suggest that results should be interpreted with caution, especially for CAPE and CP across tropics where uncertainty is the highest and reliable long-term rawinsonde observations are missing.

scholarly journals Surface matters: limitations of CALIPSO V3 aerosol typing in coastal regions

2014 ◽  
Vol 7 (7) ◽  
pp. 2061-2072 ◽  
Author(s):  
T. Kanitz ◽  
A. Ansmann ◽  
A. Foth ◽  
P. Seifert ◽  
U. Wandinger ◽  
...  
Keyword(s):  
Data Analysis ◽  
Climate Models ◽  
Global Climate ◽  
Coastal Areas ◽  
Global Climate Models ◽  
Important Input ◽  
High Fraction ◽  
Ground Based Lidar

Abstract. In the CALIPSO data analysis, surface type (land/ocean) is used to augment the aerosol characterization. However, this surface-dependent aerosol typing prohibits a correct classification of marine aerosol over land that is advected from ocean to land. This might result in a systematic overestimation of the particle extinction coefficient and of the aerosol optical thickness (AOT) of up to a factor of 3.5 over land in coastal areas. We present a long-term comparison of CALIPSO and ground-based lidar observations of the aerosol conditions in the coastal environment of southern South America (Punta Arenas, Chile, 53° S), performed in December 2009–April 2010. Punta Arenas is almost entirely influenced by marine particles throughout the year, indicated by a rather low AOT of 0.02–0.04. However, we found an unexpectedly high fraction of continental aerosol in the aerosol types inferred by means of CALIOP observations and, correspondingly, too high values of particle extinction. Similar features of the CALIOP data analysis are presented for four other coastal areas around the world. Since CALIOP data serve as important input for global climate models, the influence of this systematic error was estimated by means of simplified radiative-transfer calculations.

scholarly journals Back to the Future: Using Long-Term Observational and Paleo-Proxy Reconstructions to Improve Model Projections of Antarctic Climate

Geosciences ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 255 ◽  
Author(s):  
Thomas J. Bracegirdle ◽  
Florence Colleoni ◽  
Nerilie J. Abram ◽  
Nancy A. N. Bertler ◽  
Daniel A. Dixon ◽  
...  
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Global Climate ◽  
Ice Core ◽  
Global Climate Models ◽  
Climate Projections ◽  
Past Performance ◽  
Wide Range ◽  
Proxy Reconstructions

Quantitative estimates of future Antarctic climate change are derived from numerical global climate models. Evaluation of the reliability of climate model projections involves many lines of evidence on past performance combined with knowledge of the processes that need to be represented. Routine model evaluation is mainly based on the modern observational period, which started with the establishment of a network of Antarctic weather stations in 1957/58. This period is too short to evaluate many fundamental aspects of the Antarctic and Southern Ocean climate system, such as decadal-to-century time-scale climate variability and trends. To help address this gap, we present a new evaluation of potential ways in which long-term observational and paleo-proxy reconstructions may be used, with a particular focus on improving projections. A wide range of data sources and time periods is included, ranging from ship observations of the early 20th century to ice core records spanning hundreds to hundreds of thousands of years to sediment records dating back 34 million years. We conclude that paleo-proxy records and long-term observational datasets are an underused resource in terms of strategies for improving Antarctic climate projections for the 21st century and beyond. We identify priorities and suggest next steps to addressing this.

scholarly journals Varying soil moisture-atmosphere feedbacks explain divergent temperature extremes and precipitation projections in Central Europe

2018 ◽  
Author(s):  
Martha M. Vogel ◽  
Jakob Zscheischler ◽  
Sonia I. Seneviratne
Keyword(s):  
Climate Change ◽  
Soil Moisture ◽  
Central Europe ◽  
Climate Models ◽  
Global Climate ◽  
Summer Precipitation ◽  
Global Climate Models ◽  
Temperature Extremes ◽  
Extreme Temperatures

Abstract. The frequency and intensity of climate extremes is expected to increase in many regions due to anthropogenic climate change. In Central Europe extreme temperatures are projected to change more strongly than global mean temperatures and soil moisture-temperature feedbacks significantly contribute to this regional amplification. Because of their strong societal, ecological and economic impacts, robust projections of temperature extremes are needed. Unfortunately, in current model projections, temperature extremes in Central Europe are prone to large uncertainties. In order to understand and potentially reduce uncertainties of extreme temperatures projections in Europe, we analyze global climate models from the CMIP5 ensemble for the business-as-usual high-emission scenario (RCP8.5). We find a divergent behavior in long-term projections of summer precipitation until the end of the 21st century, resulting in a trimodal distribution of precipitation (wet, dry and very dry). All model groups show distinct characteristics for summer latent heat flux, top soil moisture, and temperatures on the hottest day of the year (TXx), whereas for net radiation and large-scale circulation no clear trimodal behavior is detectable. This suggests that different land-atmosphere coupling strengths may be able to explain the uncertainties in temperature extremes. Constraining the full model ensemble with observed present-day correlations between summer precipitation and TXx excludes most of the very dry and dry models. In particular, the very dry models tend to overestimate the negative coupling between precipitation and TXx, resulting in a too strong warming. This is particularly relevant for global warming levels above 2 °C. The analysis allows for the first time to substantially reduce uncertainties in the projected changes of TXx in global climate models. Our results suggest that long-term temperature changes in TXx in Central Europe are about 20 % lower than projected by the multi-model median of the full ensemble. In addition, mean summer precipitation is found to be more likely to stay close to present-day levels. These results are highly relevant for improving estimates of regional climate-change impacts including heat stress, water supply and crop failure for Central Europe.

The Double-ITCZ Bias in CMIP6 Models

2020 ◽  
Author(s):  
Baijun Tian
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Coupled Model ◽  
Global Climate Models ◽  
Cmip5 Models ◽  
Tropical Precipitation ◽  
Double Itcz ◽  
Intercomparison Project ◽  
Fully Coupled

&lt;p&gt;The double-Intertropical Convergence Zone (ITCZ) bias is one of the most outstanding problems in climate models. This study seeks to examine the double-ITCZ bias in the latest state-of-the-art fully coupled global climate models that participated in Coupled Model Intercomparison Project (CMIP) Phase 6 (CMIP6) in comparison to their previous generations (CMIP3 and CMIP5 models). To that end, we have analyzed the long-term annual mean tropical precipitation distributions and several precipitation bias indices that quantify the double-ITCZ biases in 75 climate models including 24 CMIP3 models, 25 CMIP3 models, and 26 CMIP6 models. We find that the double-ITCZ bias and its big inter-model spread persist in CMIP6 models but the double-ITCZ bias is slightly reduced from CMIP3 or CMIP5 models to CMIP6 models.&lt;/p&gt;

Comparison of Short-Term and Long-Term Radiative Feedbacks and Variability in Twentieth-Century Global Climate Model Simulations

2013 ◽  
Vol 26 (24) ◽  
pp. 10051-10070 ◽  
Author(s):  
Meghan M. Dalton ◽  
Karen M. Shell
Keyword(s):  
Twentieth Century ◽  
Water Vapor ◽  
Climate Sensitivity ◽  
Surface Albedo ◽  
Global Climate ◽  
Global Climate Model ◽  
Atmospheric Temperature ◽  
Global Climate Models ◽  
Short Term

Abstract The climate sensitivity uncertainty of global climate models (GCMs) is partly due to the spread of individual feedbacks. One approach to constrain long-term climate sensitivity is to use the relatively short observational record, assuming there exists some relationship in feedbacks between short and long records. The present work tests this assumption by regressing short-term feedback metrics, characterized by the 20-yr feedback as well as interannual and intra-annual metrics, against long-term longwave water vapor, longwave atmospheric temperature, and shortwave surface albedo feedbacks calculated from 13 twentieth-century GCM simulations. Estimates of long-term feedbacks derived from reanalysis observations and statistically significant regressions are consistent with but no more constrained than earlier estimates. For the interannual metric, natural variability contributes to the feedback uncertainty, reducing the ability to estimate the interannual behavior from one 20-yr time slice. For both the interannual and intra-annual metrics, uncertainty in the intermodel relationships between 20-yr metrics and 100-yr feedbacks also contributes to the feedback uncertainty. Because of differences in time scales of feedback processes, relationships between the 20-yr interannual metric and 100-yr water vapor and atmospheric temperature feedbacks are significant for only one feedback calculation method. The intra-annual and surface albedo relationships show more complex behavior, though positive correspondence between Northern Hemisphere surface albedo intra-annual metrics and 100-yr feedbacks is consistent with previous studies. Many relationships between 20-yr metrics and 100-yr feedbacks are sensitive to the specific GCMs included, highlighting that care should be taken when inferring long-term feedbacks from short-term observations.

scholarly journals Blue Water in Europe: Estimates of Current and Future Availability and Analysis of Uncertainty

Water ◽  
2019 ◽  
Vol 11 (3) ◽  
pp. 420 ◽  
Author(s):  
Alvaro Sordo-Ward ◽  
Isabel Granados ◽  
Ana Iglesias ◽  
Luis Garrote
Keyword(s):  
High Resolution ◽  
Water Availability ◽  
Climate Models ◽  
Climate Model ◽  
Global Climate ◽  
Baseline Period ◽  
Global Climate Models ◽  
Blue Water ◽  
Large Area

This study presents a regional assessment of future blue water availability in Europe under different assumptions. The baseline period (1960 to 1999) is compared to the near future (2020 to 2059) and the long-term future (2060 to 2099). Blue water availability is estimated as the maximum amount of water supplied at a certain point of the river network that satisfies a defined demand, taking into account specified reliability requirements. Water availability is computed with the geospatial high-resolution Water Availability and Adaptation Policy Assessment (WAAPA) model. The WAAPA model definition for this study extends over 6 million km2 in Europe and considers almost 4000 sub-basins in Europe. The model takes into account 2300 reservoirs larger than 5 hm3, and the dataset of Hydro 1k with 1700 sub-basins. Hydrological scenarios for this study were taken from the Inter-Sectoral Impact Model Inter-Comparison Project and included simulations of five global climate models under different Representative Concentration Pathways scenarios. The choice of method is useful for evaluating large area regional studies that include high resolution on the systems´ characterization. The results highlight large uncertainties associated with a set of local water availability estimates across Europe. Climate model uncertainties for mean annual runoff and potential water availability were found to be higher than scenario uncertainties. Furthermore, the existing hydraulic infrastructure and its management have played an important role by decoupling water availability from hydrologic variability. This is observed for all climate models, the emissions scenarios considered, and for near and long-term future. The balance between water availability and withdrawals is threatened in some regions, such as the Mediterranean region. The results of this study contribute to defining potential challenges in water resource systems and regional risk areas.

scholarly journals Black Carbon Measurements in the Arctic Get an Upgrade

Eos ◽  
2017 ◽  
Author(s):  
Sarah Stanley
Keyword(s):  
Black Carbon ◽  
Climate Models ◽  
Global Climate ◽  
Global Climate Models ◽  
Arctic Climate ◽  
The Arctic ◽  
Term Data

Long-term data of higher accuracy could help improve global climate models and reveal trends in black carbon’s influence on Arctic climate.

Long-term variability of shortwave absorption under abrupt-4xCO2 climate forcing and its visible and near-IR contributions

2020 ◽  
Author(s):  
Maria Z. Hakuba ◽  
Alejandro Bodas-Salcedo ◽  
Graeme Stephens
Keyword(s):  
Global Warming ◽  
Near Infrared ◽  
Climate Models ◽  
Global Climate ◽  
Global Climate Models ◽  
Climate Forcing ◽  
Shortwave Radiation ◽  
Hemispheric Differences ◽  
Climate Feedbacks

&lt;p&gt;While ongoing global warming is largely the result of reduced outgoing longwave radiation (OLR), climate feedbacks associated with changes in atmospheric water vapor and surface albedo are expected to enhance the absorption of shortwave radiation (ASR) and to sustain global warming on centennial time scales beyond the OLR modulations. These feedbacks as well as positive cloud feedbacks reduce the reflected shortwave (SW) flux at the top-of-atmosphere (TOA) and are a result of scattering and absorbing processes that differ by their near-infrared (NIR) and visible (VIS) contributions. Since direct measurements of broadband NIR (~0.7-5 mm) and VIS (~0.2-0.7 mm) radiation flux do not exist, we utilize UKESM1 simulations to study SW, NIR, and VIS climate feedbacks under preindustrial and abrupt-4xCO&lt;sub&gt;2&lt;/sub&gt; climate forcing.&lt;/p&gt;&lt;p&gt;Besides its global long-term behavior, the spatial variability and key physical controls of ASR are not well characterized either. A prominent example is the unexplained hemispheric symmetry in planetary albedo that is consistently missed by current global climate models yielding unrealistic precipitation and circulation patterns. Although energetically equivalent, the observed hemispheric albedos differ spectrally, reflecting the uneven distribution of clouds and land masses. We use the same UKESM1 simulations to contrast inter-hemispheric differences in SW, NIR and VIS, and their relation to changes in clouds, the gaseous atmosphere and surface properties to shed light on processes relevant to the present-day symmetry, model biases, and potential future changes.&lt;/p&gt;

scholarly journals Updated world map of the Köppen-Geiger climate classification

2007 ◽  
Vol 11 (5) ◽  
pp. 1633-1644 ◽  
Author(s):  
M. C. Peel ◽  
B. L. Finlayson ◽  
T. A. McMahon
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Global Climate Models ◽  
Monthly Precipitation ◽  
Climate Type ◽  
Data Set ◽  
Supplementary Material ◽  
Global Data

Abstract. Although now over 100 years old, the classification of climate originally formulated by Wladimir Köppen and modified by his collaborators and successors, is still in widespread use. It is widely used in teaching school and undergraduate courses on climate. It is also still in regular use by researchers across a range of disciplines as a basis for climatic regionalisation of variables and for assessing the output of global climate models. Here we have produced a new global map of climate using the Köppen-Geiger system based on a large global data set of long-term monthly precipitation and temperature station time series. Climatic variables used in the Köppen-Geiger system were calculated at each station and interpolated between stations using a two-dimensional (latitude and longitude) thin-plate spline with tension onto a 0.1°×0.1° grid for each continent. We discuss some problems in dealing with sites that are not uniquely classified into one climate type by the Köppen-Geiger system and assess the outcomes on a continent by continent basis. Globally the most common climate type by land area is BWh (14.2%, Hot desert) followed by Aw (11.5%, Tropical savannah). The updated world Köppen-Geiger climate map is freely available electronically in the Supplementary Material Section.

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