Autumn Precipitation Trends over Southern Hemisphere Midlatitudes as Simulated by CMIP5 Models

Abstract In recent decades, Southern Hemisphere midlatitude regions such as southern Africa, southeastern Australia, and southern Chile have experienced a reduction in austral autumn precipitation; the cause of which is poorly understood. This study focuses on the ability of global climate models that form part of the Coupled Model Intercomparison Project phase 5 to simulate these trends, their relationship with extratropical and subtropical processes, and implications for future precipitation changes. Models underestimate both the historical autumn poleward expansion of the subtropical dry zone and the positive southern annular mode (SAM) trend. The multimodel ensemble (MME) is also unable to capture the spatial pattern of observed precipitation trends across semiarid midlatitude regions. However, in temperate regions that are located farther poleward such as southern Chile, the MME simulates observed precipitation declines. The MME shows a strong consensus in twenty-first-century declines in autumn precipitation across southern Chile in both the medium–low and high representative concentration pathway (RCP) scenarios and across southern Africa in the high RCP scenario, but little change across southeastern Australia. Projecting a strong positive SAM trend and continued subtropical dry-zone expansion, the models converge on large SAM and dry-zone-expansion-induced precipitation declines across southern midlatitudes. In these regions, the strength of future precipitation trends is proportional to the strength of modeled trends in these phenomena, suggesting that unabated greenhouse gas–induced climate change will have a large impact on austral autumn precipitation in such midlatitude regions.

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Reexamining the Relationship between Climate Sensitivity and the Southern Hemisphere Radiation Budget in CMIP Models

Journal of Climate ◽

10.1175/jcli-d-15-0031.1 ◽

2015 ◽

Vol 28 (23) ◽

pp. 9298-9312 ◽

Cited By ~ 17

Author(s):

Kevin M. Grise ◽

Lorenzo M. Polvani ◽

John T. Fasullo

Keyword(s):

Southern Ocean ◽

Southern Hemisphere ◽

Climate Sensitivity ◽

Climate Models ◽

Global Climate ◽

Global Climate Models ◽

Radiation Budget ◽

Cmip5 Models ◽

Net Radiation ◽

Subtropical Clouds

Abstract Recent efforts to narrow the spread in equilibrium climate sensitivity (ECS) across global climate models have focused on identifying observationally based constraints, which are rooted in empirical correlations between ECS and biases in the models’ present-day climate. This study reexamines one such constraint identified from CMIP3 models: the linkage between ECS and net top-of-the-atmosphere radiation biases in the Southern Hemisphere (SH). As previously documented, the intermodel spread in the ECS of CMIP3 models is linked to present-day cloud and net radiation biases over the midlatitude Southern Ocean, where higher cloud fraction in the present-day climate is associated with larger values of ECS. However, in this study, no physical explanation is found to support this relationship. Furthermore, it is shown here that this relationship disappears in CMIP5 models and is unique to a subset of CMIP models characterized by unrealistically bright present-day clouds in the SH subtropics. In view of this evidence, Southern Ocean cloud and net radiation biases appear inappropriate for providing observationally based constraints on ECS. Instead of the Southern Ocean, this study points to the stratocumulus-to-cumulus transition regions of the SH subtropical oceans as key to explaining the intermodel spread in the ECS of both CMIP3 and CMIP5 models. In these regions, ECS is linked to present-day cloud and net radiation biases with a plausible physical mechanism: models with brighter subtropical clouds in the present-day climate show greater ECS because 1) subtropical clouds dissipate with increasing CO2 concentrations in many models and 2) the dissipation of brighter clouds contributes to greater solar warming of the surface.

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Precipitation Associated with Cyclogenetic Hotspot Regions in the Extratropical Southern Hemisphere: CORDEX-CORE Projections

10.5194/egusphere-egu2020-3147 ◽

2020 ◽

Author(s):

Michelle Reboita ◽

Marco Reale ◽

Rosmeri da Rocha ◽

Graziano Giuliani ◽

Erika Coppola ◽

...

Keyword(s):

Southern Hemisphere ◽

Climate Models ◽

Climate Model ◽

Global Climate ◽

Regional Climate ◽

Winter Season ◽

Coupled Model ◽

Global Climate Models ◽

Precipitation Intensity ◽

Southeastern Australia

Projections of the precipitation associated with cyclones in the main cyclogenetic regions of the Extratropical Southern Hemisphere domains (Africa - AFR, Australia - AUS and South America - SAM) are here analyzed during the winter season (JJA). The projections were obtained with the Regional Climate Model version 4 (RegCM4) nested in three global climate models (GCMs) from the Coupled Model Intercomparison Project phase 5 (CMIP5) under the Representative Concentration Pathway 8.5. RegCM4 simulations were executed with horizontal grid spacing of 25 km and for the period 1979-2100. As reference period, we consider the interval 1995-2014 and as future climate, the period 2080-2099. Cyclones are identified using an algorithm based on the neighbor nearest approach applied to 6 hourly mean sea level pressure (SLP) fields. In SAM and AUS domains, two hotspot regions for cyclogenesis are selected while for AFR only one is considered. First, in each hotspot region, the cyclogeneses are identified and, then, the mean precipitation from the previous day (day-1) to the day after (day+1) of these processes is calculated. A general negative trend in the cyclone's frequency is projected for the period 2080-2099. However, for the same period, it is projected an increase of precipitation intensity for AFR domain, mainly near the southwestern coast of the continent. In AUS the increase is observed between southeastern Australia and New Zeland, and over north New Zealand. For SAM there is an expansion of the area with a maximum precipitation intensity close to southern Brazil and Uruguay and to the east of 60oW near 40oS. Summarizing, the precipitation associated with individual cyclones will increase on average in the future (for example 30% in the SAM domain), being the storms less frequent but more intense.

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Multi-Decadal Variability and Future Changes in Precipitation over Southern Africa

Atmosphere ◽

10.3390/atmos12060742 ◽

2021 ◽

Vol 12 (6) ◽

pp. 742

Author(s):

Kenny Thiam Choy Lim Kam Sian ◽

Jianhong Wang ◽

Brian Odhiambo Ayugi ◽

Isaac Kwesi Nooni ◽

Victor Ongoma

Keyword(s):

Southern Africa ◽

Climate Models ◽

Decadal Variability ◽

Global Climate ◽

Spatial Scales ◽

Precipitation Amount ◽

High Elevation ◽

Global Climate Models ◽

Initial Increase ◽

Precipitation Trends

The future planning and management of water resources ought to be based on climate change projections at relevant temporal and spatial scales. This work uses the new regional demarcation for Southern Africa (SA) to investigate the spatio-temporal precipitation variability and trends of centennial-scale observation and modeled data, based on datasets from the sixth phase of the Coupled Model Intercomparison Project (CMIP6). The study employs several statistical methods to rank the models according to their precipitation simulation ability. The Theil–Sen slope estimator is used to assess precipitation trends, with a Student’s t-test for the significance test. The comparison of observation and model historical data enables identification of the best-performing global climate models (GCMs), which are then employed in the projection analysis under two Shared Socioeconomic Pathways (SSPs): SSP2-4.5 and SSP5-8.5. The GCMs adequately capture the annual precipitation variation but with a general overestimation, especially over high-elevation areas. Most of the models fail to capture precipitation over the Lesotho-Eswatini area. The three best-performing GCMs over SA are FGOALS-g3, MPI-ESM1-2-HR and NorESM2-LM. The sub-regions demonstrate that precipitation trends cannot be generalized and that localized studies can provide more accurate findings. Overall, precipitation in the wet and dry seasons shows an initial increase during the near future over western and eastern SA, followed by a reduction in precipitation during the mid- and far future under both projection scenarios. Madagascar is expected to experience a decrease in precipitation amount throughout the twenty-first century.

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Drivers of Twenty-First Century U.S. Winter Precipitation Trends in CMIP6 Models: A Storyline-Based Approach

Journal of Climate ◽

10.1175/jcli-d-21-0080.1 ◽

2021 ◽

pp. 1-48

Author(s):

Daniel F. Schmidt ◽

Kevin M. Grise

Keyword(s):

Climate Models ◽

Southern Oscillation ◽

Global Climate ◽

The United States ◽

Winter Precipitation ◽

Global Climate Models ◽

First Century ◽

Precipitation Trend ◽

Twenty First Century ◽

Precipitation Trends

AbstractClimate change during the twenty-first century has the potential to substantially alter geographic patterns of precipitation. However, regional precipitation changes can be very difficult to project, and in some regions, global climate models do not even agree on the sign of the precipitation trend. Since some of this uncertainty is due to internal variability rather than model bias, models cannot be used to narrow the possibilities to a single outcome, but they can usefully quantify the range of plausible outcomes and identify the combination of dynamical drivers that would be likely to produce each.This study uses a storylines approach—a type of regression-based analysis—to identify some of the key dynamical drivers that explain the variance in 21st century U.S. winter precipitation trends across CMIP6 models under the SSP3-7.0 emissions scenario. This analysis shows that the spread in precipitation trends is not primarily driven by differences in modeled climate sensitivity. Key drivers include global-mean surface temperature, but also tropical upper-troposphere temperature, the El Niño-Southern Oscillation (ENSO), the Pacific-North America (PNA) pattern, and the East Pacific (EP) dipole (a dipole pattern in geopotential heights over North America’s Pacific coast). Combinations of these drivers can reinforce or cancel to produce various high- or low-impact scenarios for winter precipitation trends in various regions of the United States. For example, the most extreme winter precipitation trends in the southwestern U.S. result from opposite trends in ENSO and EP, whereas the wettest winter precipitation trends in the midwestern U.S. result from a combination of strong global warming and a negative PNA trend.

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Southern Hemisphere Continental Temperature Responses to Major Volcanic Eruptions Since 1883 in CMIP5 Models

10.21203/rs.3.rs-310211/v1 ◽

2021 ◽

Author(s):

Pamela J Harvey ◽

Stefan W Grab

Keyword(s):

Southern Hemisphere ◽

Temperature Response ◽

Volcanic Eruptions ◽

Lag Time ◽

Cmip5 Models ◽

Seasonal Temperature ◽

Near Surface ◽

Santa Maria ◽

Temperature Responses ◽

Austral Autumn

Abstract Although global and Northern Hemisphere (NH) temperature responses to volcanic forcing have been extensively investigated, knowledge of such responses over Southern Hemisphere (SH) continental regions is still limited. Here we use an ensemble of CMIP5 models to explore SH temperature responses to four major volcanic eruptions: Krakatau (1883), Santa Maria (1902), Agung (1963) and Pinatubo (1991). Focus is on near-surface temperature responses over southern continental landmasses including southern South America (SSA), southern Africa (SAF) and Australia and their seasonal differences. Findings indicate that for all continents, temperature responses were strongest and lasted longest following the Krakatau eruption. Responses in Australia had the shortest lag time, strongest maximum seasonal response, as well as the most significant monthly anomalies. In contrast, SSA records the longest lag time, weakest maximum seasonal temperature response, and lowest number of monthly negative anomalies following these eruptions. In most cases, the strongest single-season response occurred in austral autumn or winter, and the weakest in summer or spring. We tentatively propose that cooler temperature responses are likely caused, at least in part, by the intensification of the westerlies and associated mid-latitude cyclones and anti-cyclones.

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Fidelity of the Observational/Reanalysis Datasets and Global Climate Models in Representation of Extreme Precipitation in East China

Journal of Climate ◽

10.1175/jcli-d-18-0104.1 ◽

2018 ◽

Vol 32 (1) ◽

pp. 195-212 ◽

Cited By ~ 9

Author(s):

Sicheng He ◽

Jing Yang ◽

Qing Bao ◽

Lei Wang ◽

Bin Wang

Keyword(s):

Extreme Precipitation ◽

Climate Models ◽

Climate Model ◽

Global Climate ◽

Yangtze River Basin ◽

Global Climate Model ◽

Global Climate Models ◽

Global Ocean ◽

East China ◽

Cmip5 Models

AbstractRealistic reproduction of historical extreme precipitation has been challenging for both reanalysis and global climate model (GCM) simulations. This work assessed the fidelities of the combined gridded observational datasets, reanalysis datasets, and GCMs [CMIP5 and the Chinese Academy of Sciences Flexible Global Ocean–Atmospheric Land System Model–Finite-Volume Atmospheric Model, version 2 (FGOALS-f2)] in representing extreme precipitation over East China. The assessment used 552 stations’ rain gauge data as ground truth and focused on the probability distribution function of daily precipitation and spatial structure of extreme precipitation days. The TRMM observation displays similar rainfall intensity–frequency distributions as the stations. However, three combined gridded observational datasets, four reanalysis datasets, and most of the CMIP5 models cannot capture extreme precipitation exceeding 150 mm day−1, and all underestimate extreme precipitation frequency. The observed spatial distribution of extreme precipitation exhibits two maximum centers, located over the lower-middle reach of Yangtze River basin and the deep South China region, respectively. Combined gridded observations and JRA-55 capture these two centers, but ERA-Interim, MERRA, and CFSR and almost all CMIP5 models fail to capture them. The percentage of extreme rainfall in the total rainfall amount is generally underestimated by 25%–75% in all CMIP5 models. Higher-resolution models tend to have better performance, and physical parameterization may be crucial for simulating correct extreme precipitation. The performances are significantly improved in the newly released FGOALS-f2 as a result of increased resolution and a more realistic simulation of moisture and heating profiles. This work pinpoints the common biases in the combined gridded observational datasets and reanalysis datasets and helps to improve models’ simulation of extreme precipitation, which is critically important for reliable projection of future changes in extreme precipitation.

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Numerical simulation of surface solar radiation over Southern Africa. Part 1: Evaluation of regional and global climate models

Climate Dynamics ◽

10.1007/s00382-018-4143-1 ◽

2018 ◽

Vol 52 (1-2) ◽

pp. 457-477 ◽

Cited By ~ 9

Author(s):

Chao Tang ◽

Béatrice Morel ◽

Martin Wild ◽

Benjamin Pohl ◽

Babatunde Abiodun ◽

...

Keyword(s):

Numerical Simulation ◽

Solar Radiation ◽

Southern Africa ◽

Climate Models ◽

Global Climate ◽

Global Climate Models ◽

Surface Solar Radiation

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The Double-ITCZ Bias in CMIP6 Models

10.5194/egusphere-egu2020-21375 ◽

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

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.

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Regionally Varying Assessments of Upper-Level Tropical Width in Reanalyses and CMIP5 Models Using a Tropopause Break Metric

Journal of Climate ◽

10.1175/jcli-d-19-0629.1 ◽

2020 ◽

Vol 33 (14) ◽

pp. 5885-5903 ◽

Cited By ~ 1

Author(s):

Elinor R. Martin ◽

Cameron R. Homeyer ◽

Roarke A. McKinzie ◽

Kevin M. McCarthy ◽

Tao Xian

Keyword(s):

Climate Models ◽

Climate Model ◽

Global Climate ◽

Global Climate Models ◽

Cmip5 Models ◽

The Past ◽

East Pacific ◽

Change Climate ◽

Upper Level ◽

The Tropics

AbstractChanges in tropical width can have important consequences in sectors including ecosystems, agriculture, and health. Observations suggest tropical expansion over the past 30 years although studies have not agreed on the magnitude of this change. Climate model projections have also indicated an expansion and show similar uncertainty in its magnitude. This study utilizes an objective, longitudinally varying, tropopause break method to define the extent of the tropics at upper levels. The location of the tropopause break is associated with enhanced stratosphere–troposphere exchange and thus its structure influences the chemical composition of the stratosphere. The method shows regional variations in the width of the upper-level tropics in the past and future. Four modern reanalyses show significant contraction of the tropics over the eastern Pacific between 1981 and 2015, and slight but significant expansion in other regions. The east Pacific narrowing contributes to zonal mean narrowing, contradicting prior work, and is attributed to the use of monthly and zonal mean data in prior studies. Six global climate models perform well in representing the climatological location of the tropical boundary. Future projections show a spread in the width trend (from ~0.5° decade−1 of narrowing to ~0.4° decade−1 of widening), with a narrowing projected across the east Pacific and Northern Hemisphere Americas. This study illustrates that this objective tropopause break method that uses instantaneous data and does not require zonal averaging is appropriate for identifying upper-level tropical width trends and the break location is connected with local and regional changes in precipitation.

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Effects of Convective Gravity Wave Drag in the Southern Hemisphere Winter Stratosphere

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-12-0238.1 ◽

2013 ◽

Vol 70 (7) ◽

pp. 2120-2136 ◽

Cited By ~ 20

Author(s):

Hyun-Joo Choi ◽

Hye-Yeong Chun

Keyword(s):

Gravity Wave ◽

Southern Hemisphere ◽

Climate Models ◽

Climate Model ◽

Global Climate ◽

Storm Track ◽

Wave Drag ◽

Global Climate Models ◽

Systematic Biases ◽

Hemisphere Winter

Abstract The excessively strong polar jet and cold pole in the Southern Hemisphere winter stratosphere are systematic biases in most global climate models and are related to underestimated wave drag in the winter extratropical stratosphere—namely, missing gravity wave drag (GWD). Cumulus convection is strong in the winter extratropics in association with storm-track regions; thus, convective GWD could be one of the missing GWDs in models that do not adopt source-based nonorographic GWD parameterizations. In this study, the authors use the Whole Atmosphere Community Climate Model (WACCM) and show that the zonal-mean wind and temperature biases in the Southern Hemisphere winter stratosphere of the model are significantly alleviated by including convective GWD (GWDC) parameterizations. The reduction in the wind biases is due to enhanced wave drag in the winter extratropical stratosphere, which is caused directly by the additional GWDC and indirectly by the increased existing nonorographic GWD and resolved wave drag in response to the GWDC. The cold temperature biases are alleviated by increased downwelling in the winter polar stratosphere, which stems from an increased poleward motion due to enhanced wave drag in the winter extratropical stratosphere. A comparison between two simulations separately using the ray-based and columnar GWDC parameterizations shows that the polar night jet with a ray-based GWDC parameterization is much more realistic than that with a columnar GWDC parameterization.

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