scholarly journals Can Climate Models Simulate the Observed Strong Summer Surface Cooling in the Equatorial Atlantic?

2018 ◽  
pp. 7-23
Author(s):  
Tina Dippe ◽  
Martin Krebs ◽  
Jan Harlaß ◽  
Joke F. Lübbecke
Keyword(s):  
Climate Models ◽  
Equatorial Atlantic ◽  
Surface Cooling

scholarly journals A satellite era warming hole in the equatorial Atlantic Ocean

2020 ◽  
Author(s):  
Hyacinth Nnamchi ◽  
Mojib Latif ◽  
Noel Keenlyside ◽  
Wonsun Park
Keyword(s):  
Surface Temperature ◽  
Ocean Circulation ◽  
Climate Models ◽  
Ocean Surface ◽  
Boreal Summer ◽  
Cold Tongue ◽  
Intrinsic Variability ◽  
Equatorial Atlantic ◽  
Surface Cooling ◽  
Surface Warming

<p>Although the globally averaged surface temperature of the Earth has considerably warmed since the beginning of global satellite measurements in 1979, a warming hole, with hardly any surface warming that is most pronounced in boreal summer, has been observed in the equatorial Atlantic region during this period. The warming hole occurs in an extended area of the equatorial Atlantic that includes the cold tongue, the region of locally cooler ocean surface waters that develops just south of the equator in boreal summer, partly reflecting the upwelling of deep cold waters by the action of the southeasterly trade winds. This lack of surface warming of the cold tongue denotes an 11% amplification of the mean annual cycle of the sea surface temperature during the satellite era. The warming hole is driven by an intensification of the equatorial upwelling of cold waters into the ocean surface layers and damped by the surface heat flux. In observations, the tendency for surface cooling appears to reflect intrinsic variability of the climate system and is not unusual during the instrumental period. The warming hole is associated with wind-induced ocean circulation changes to the south and north of the northward of the equator. Coupled model ensembles forced by the observed varying concentrations of atmospheric greenhouse gases and natural aerosols as well as unforced runs were analyzed. The ensembles suggest a strong role for atmospheric aerosols in the warming hole. However, although aerosols can cause a cooling of the cold tongue, intrinsic climate variability as represented in the unforced experiment can potentially cause larger cooling than has been observed during the satellite era. This study highlights the difficulty in reconciling observations and the climate models for the attribution of the warming hole.</p>

scholarly journals Extreme heat in India and anthropogenic climate change

2018 ◽  
Vol 18 (1) ◽  
pp. 365-381 ◽  
Author(s):  
Geert Jan van Oldenborgh ◽  
Sjoukje Philip ◽  
Sarah Kew ◽  
Michiel van Weele ◽  
Peter Uhe ◽  
...  
Keyword(s):  
Air Pollution ◽  
Global Warming ◽  
Health Effects ◽  
Climate Models ◽  
Decadal Variability ◽  
Heat Waves ◽  
Health Impact ◽  
Heat Index ◽  
Maximum Temperature ◽  
Surface Cooling

Abstract. On 19 May 2016 the afternoon temperature reached 51.0 °C in Phalodi in the northwest of India – a new record for the highest observed maximum temperature in India. The previous year, a widely reported very lethal heat wave occurred in the southeast, in Andhra Pradesh and Telangana, killing thousands of people. In both cases it was widely assumed that the probability and severity of heat waves in India are increasing due to global warming, as they do in other parts of the world. However, we do not find positive trends in the highest maximum temperature of the year in most of India since the 1970s (except spurious trends due to missing data). Decadal variability cannot explain this, but both increased air pollution with aerosols blocking sunlight and increased irrigation leading to evaporative cooling have counteracted the effect of greenhouse gases up to now. Current climate models do not represent these processes well and hence cannot be used to attribute heat waves in this area. The health effects of heat are often described better by a combination of temperature and humidity, such as a heat index or wet bulb temperature. Due to the increase in humidity from irrigation and higher sea surface temperatures (SSTs), these indices have increased over the last decades even when extreme temperatures have not. The extreme air pollution also exacerbates the health impacts of heat. From these factors it follows that, from a health impact point of view, the severity of heat waves has increased in India. For the next decades we expect the trend due to global warming to continue but the surface cooling effect of aerosols to diminish as air quality controls are implemented. The expansion of irrigation will likely continue, though at a slower pace, mitigating this trend somewhat. Humidity will probably continue to rise. The combination will result in a strong rise in the temperature of heat waves. The high humidity will make health effects worse, whereas decreased air pollution would decrease the impacts.

scholarly journals Mechanisms of Future Changes in Equatorial Upwelling: CMIP5 Intermodel Analysis

2020 ◽  
Vol 33 (2) ◽  
pp. 497-510 ◽  
Author(s):  
Mio Terada ◽  
Shoshiro Minobe ◽  
Curtis Deutsch
Keyword(s):  
Climate Models ◽  
Eastern Pacific ◽  
Trade Wind ◽  
Pacific Basin ◽  
Ekman Pumping ◽  
Equatorial Atlantic ◽  
Western Atlantic ◽  
Near Surface ◽  
The Pacific ◽  
Equatorial Upwelling

AbstractThe future change in equatorial upwelling between 1971–2000 and 2071–2100 is investigated using data from 24 coupled climate models. The multimodel ensemble (MME) mean exhibits substantial equatorial upwelling decrease in the eastern Pacific and weaker decrease in the western Atlantic Ocean. The MME mean of upwelling change and intermodel variation of that are decomposed into distinct isopycnal and diapycnal components. In the Pacific, the diapycnal upwelling decreases near the surface, associated with a weakened Ekman pumping. The isopycnal upwelling decreases at depths of 75–200 m around the core of the Equatorial Undercurrent (EUC) due to flattening of the density layer in which it flows. Both the weakened Ekman pumping and the EUC flattening are induced by the locally weakened trade wind over the eastern Pacific basin. In the equatorial Atlantic, both the change in MME mean and the intermodel variation of upwellings are significantly related to the weakened trade wind and enhanced stratification, although these drivers are not independent. The results for the Pacific Ocean imply that future reduction in upwelling may have impacts at different depths by different mechanisms. In particular, the rapid warming of sea surface temperature in the eastern Pacific basin may be mainly caused by the near-surface diapycnal upwelling reduction rather than isopycnal upwelling reduction associated EUC flattening, which is important at deeper levels.

scholarly journals Magnitude and timing of Equatorial Atlantic surface warming during the last glacial bipolar oscillations

2012 ◽  
Vol 8 (3) ◽  
pp. 1737-1762
Author(s):  
S. Weldeab
Keyword(s):  
Surface Water ◽  
Spatial Heterogeneity ◽  
Ocean Circulation ◽  
Close Correlation ◽  
Core Sample ◽  
Equatorial Atlantic ◽  
Surface Cooling ◽  
Last Glacial ◽  
Heinrich Events ◽  
The Last Glacial

Abstract. We present core top and down core sample analyses of Mg/Ca in tests of planktonic foraminifer Globigerinoides ruber (variety pink) from the eastern Tropical-Equatorial Atlantic. Multivariate analysis of the core top data shows that Mg/Ca varies by 8 ± 2% and 1 ± 0.9% per unit sea surface temperature (SST) (°C) and salinity (psu) changes, respectively, indicating that temperature exerts the most dominant control on planktonic foraminiferal Mg/Ca variation. A centennially resolved record of Mg/Ca-based SST estimates from the Eastern Equatorial Atlantic (EEA) exhibits a close correlation between episodes of equatorial surface water warming, the onset of massive melt-water inputs into the North Atlantic (Heinrich events H3–H6), and rapid drop of air temperature over Greenland, indicating that the Eastern Equatorial Atlantic responded very sensitively to millennial-scale bipolar oscillations of the last glacial and marine isotope stage 3. Rapid EEA SST rise between 0.8 °C and 2 °C synchronous with the onset of Heinrich events is consistent with the concept of Tropical Atlantic warmth in response to meltwater-induced perturbation of Atlantic meridional ocean circulation (AMOC). The persistence of elevated EEA SST after the abrupt termination of Heinrich events and the spatial heterogeneity pertaining the direction, magnitude, and duration of thermal changes in the Equatorial Atlantic, as indicated by our and other proxy records, is at variance with model results that suggest a basin-wide SST rise during and rapid surface cooling after the end of Heinrich events. Our study emphasizes that changes in wind fields and wind-induced low latitude zonal surface currents were crucial in shaping the spatial heterogeneity and duration of Equatorial Atlantic surface water warmth.

scholarly journals Antarctic surface temperature and elevation during the Last Glacial Maximum

Science ◽  
2021 ◽  
Vol 372 (6546) ◽  
pp. 1097-1101
Author(s):  
Christo Buizert ◽  
T. J. Fudge ◽  
William H. G. Roberts ◽  
Eric J. Steig ◽  
Sam Sherriff-Tadano ◽  
...  
Keyword(s):  
Stable Isotopes ◽  
Last Glacial Maximum ◽  
Climate Models ◽  
Global Climate ◽  
Ice Cores ◽  
Temperature Inversion ◽  
Glacial Maximum ◽  
Global Climate Models ◽  
Surface Cooling ◽  
Last Glacial

Water-stable isotopes in polar ice cores are a widely used temperature proxy in paleoclimate reconstruction, yet calibration remains challenging in East Antarctica. Here, we reconstruct the magnitude and spatial pattern of Last Glacial Maximum surface cooling in Antarctica using borehole thermometry and firn properties in seven ice cores. West Antarctic sites cooled ~10°C relative to the preindustrial period. East Antarctic sites show a range from ~4° to ~7°C cooling, which is consistent with the results of global climate models when the effects of topographic changes indicated with ice core air-content data are included, but less than those indicated with the use of water-stable isotopes calibrated against modern spatial gradients. An altered Antarctic temperature inversion during the glacial reconciles our estimates with water-isotope observations.

scholarly journals Impact of Equatorial Atlantic Variability on ENSO Predictive Skill

2021 ◽  
Author(s):  
Eleftheria Exarchou ◽  
Pablo Ortega ◽  
Maria Belén Rodrıguez de Fonseca ◽  
Teresa Losada Doval ◽  
Irene Polo Sanchez ◽  
...  
Keyword(s):  
Climate Models ◽  
Southern Oscillation ◽  
Sensitivity Study ◽  
Tropical Pacific ◽  
Climate Impacts ◽  
Equatorial Atlantic ◽  
Predictive Capacity ◽  
Predictive Skill ◽  
The Impact ◽  
The Tropical Pacific

<p>El Niño–Southern Oscillation (ENSO) is a key mode of climate variability with worldwide climate impacts. Recent studies have highlighted the impact of other tropical oceans on its variability. In particular, observations have demonstrated that summer Atlantic Niños (Niñas) favor the development of Pacific Niñas (Niños) the following winter, but it is unclear how well climate models capture this teleconnection and its role in defining the seasonal predictive skill of ENSO. Here we use an ensemble of seasonal forecast systems to demonstrate that a better representation of equatorial Atlantic variability in summer and its lagged teleconnection mechanism with the Pacific relates to enhanced predictive capacity of autumn/winter ENSO. An additional sensitivity study further shows that correcting SST variability in equatorial Atlantic improves different aspects of forecast skill in the Tropical Pacific, boosting ENSO skill. This study thus emphasizes that new efforts to improve the representation of equatorial Atlantic variability, a region with long standing systematic model biases, can foster predictive skill in the region, the Tropical Pacific and beyond, through the global impacts of ENSO.</p>

Environmental Response in Coupled Energy and Water Cloud Impact Parameters Derived from A-Train Satellite, ERA-Interim and MERRA-2

2021 ◽  
Keyword(s):  
Climate Models ◽  
Water Cycle ◽  
Cloud Microphysics ◽  
Dynamic Regime ◽  
Radiative Heating ◽  
Radiative Effects ◽  
Surface Cooling ◽  
Heating Efficiency ◽  
Cloud Radiative Effects ◽  
Impact Parameters

Abstract Understanding the connections between latent heating from precipitation and cloud radiative effects is essential for accurately parameterizing cross-scale links between cloud microphysics and global energy and water cycles in climate models. While commonly examined separately, this study adopts two cloud impact parameters (CIPs), the surface radiative cooling efficiency, Rc, and atmospheric radiative heating efficiency, Rh, that explicitly couple cloud radiative effects and precipitation to characterize how efficiently precipitating cloud systems influence the energy budget and water cycle using A-Train observations and two reanalyses. These CIPs exhibit distinct global distributions that suggest cloud energy and water cycle coupling are highly dependent on cloud regime. The dynamic regime (ω500) controls the sign of Rh, while column water vapor (CWV) appears to be the larger control on the magnitude. The magnitude of Rc is highly coupled to the dynamic regime. Observations show that clouds cool the surface very efficiently per unit rainfall at both low and high sea surface temperature (SST) and CWV, but reanalyses only capture the former. Reanalyses fail to simulate strong Rh and moderate Rc in deep convection environments but produce stronger Rc and Rh than observations in shallow, warm rain systems in marine stratocumulus regions. While reanalyses generate fairly similar climatologies in the frequency of environmental states, the response of Rc and Rh to SST and CWV results in systematic differences in zonal and meridional gradients of cloud atmospheric heating and surface cooling relative to A-Train observations that may have significant implications for global circulations and cloud feedbacks.

Weakened impact of the Atlantic Niño on the future Guinean coast rainfall

2021 ◽  
Author(s):  
Koffi Worou ◽  
Hugues Goosse ◽  
Thierry Fichefet
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Rainfall Variability ◽  
Coupled Model ◽  
Sea Surface ◽  
Boreal Summer ◽  
Tropical Atlantic ◽  
Equatorial Atlantic ◽  
Sea Level Pressure ◽  
Guinean Coast

<p>Much of the rainfall variability in the Guinean coast area during the boreal summer is driven by the sea surface temperature (SST) variations in the eastern equatorial Atlantic, amplified by land-atmosphere interactions. This oceanic region corresponds to the center of action of the Atlantic Equatorial mode, also termed Atlantic Niño (ATL3), which is the leading SST mode of variability in the tropical Atlantic basin. In years of positive ATL3, above normal SST conditions in the ATL3 area weaken the sea level pressure gradient between the West African lands and the ocean, which in turn reduces the monsoon flow penetration into Sahel. Subsequently, the rainfall increases over the Guinean coast area. According to observations and climate models, the relation between the Atlantic Niño and the rainfall in coastal Guinea is stationary over the 20<sup>th</sup> century. While this relation remains unchanged over the 21<sup>st</sup> century in climate model projections, the strength of the teleconnection is reduced in a warmer climate. The weakened ATL3 effect on the rainfall over the tropical Atlantic (in years of positive ATL3) has been attributed to the stabilization of the atmosphere column above the tropical Atlantic. Analysis of historical and high anthropogenic emission scenario (the Shared Socioeconomic Pathways 5-8.5) simulations from 31 models participating in the sixth phase of the Coupled Model Intercomparison Project suggests an additional role of the Bjerkness feedback. A weakened SST amplitude related to ATL3 positive phases reduces the anomalous westerlies, which in turn increases the upwelling cooling effect on the sea surface. Both the Guinean coast region and the equatorial Atlantic experiment the projected rainfall reduction associated with ATL3, with a higher confidence over the ocean than over the coastal lands.</p>

The interaction between the nocturnal Amazonian low-level jet and convection in CESM

2021 ◽  
pp. 1-37
Author(s):  
Hedanqiu Bai ◽  
Courtney Schumacher
Keyword(s):  
Air Temperature ◽  
Climate Models ◽  
Coupled Model ◽  
Reanalysis Data ◽  
Equatorial Atlantic ◽  
Cold Air ◽  
Low Level ◽  
Temperature Bias ◽  
Early Afternoon ◽  
Low Level Jet

AbstractA nocturnal Amazonian low-level jet (ALLJ) was recently diagnosed using reanalysis data. This work assesses the ability of CESM1.2.2 to reproduce the jet and explores the mechanisms by which the ALLJ influences convection in the Amazon. The coupled CESM simulates the nocturnal ALLJ realistically, while CAM5 does not. A low-level cold air temperature bias in the eastern Amazon exists in CAM5, thus the ALLJ is weaker than observed. However, a cold SST bias over the equatorial North Atlantic in the coupled model offsets the cold air temperature bias, producing a realistic ALLJ. Climate models significantly underestimate March-April-May (MAM) precipitation over the eastern Amazon. We ran two sensitivity experiments using the coupled CESM by adding bottom-heavy diabatic heating at noon and midnight for 2.5 hours along the coastal Amazon during MAM to mimic the occurrence of shallow precipitating convection. When heating is added during the early afternoon, coastal convection deepens and the ALLJ transports moisture inland from the ocean, preconditioning the environment for deep convective development during the ensuing hours. The increased convection over the eastern Amazon also moderately alleviates the equatorial Atlantic westerly wind bias, leading to deepening of the east Atlantic thermocline in the following months and partially improving the simulated June-July-August (JJA) Atlantic cold tongue in the coupled model. When heating is added at night, coastal convection does not strengthen as much and the ALLJ transports less moisture. Improvements in the simulated Atlantic winds and SST are negligible. Therefore, diurnal circulations matter to the organization of convection and rain across the Amazon, with impacts over the equatorial Atlantic.

scholarly journals Impact of a new emission inventory on CAM5 simulations of aerosols and aerosol radiative effects in eastern China

2016 ◽  
Author(s):  
Tianyi Fan ◽  
Xiaohong Liu ◽  
Po-Lun Ma ◽  
Qiang Zhang ◽  
Zhanqing Li ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
Atmospheric Aerosols ◽  
Radiative Forcing ◽  
Emission Inventory ◽  
Climate Models ◽  
Eastern China ◽  
Radiative Effects ◽  
Surface Cooling ◽  
Climate Effect ◽  
Aerosol Distribution

Abstract. Emissions of aerosols and gas precursors in China have increased significantly over the past three decades with the rapid economic growth. These increases might have a large climate effect. However, global aerosol-climate models often show large biases in aerosol distribution and radiative forcing in China, and these biases are often attributed to uncertainties and biases associated with the emission inventory used to drive the models. In this study, an energy-statics and technology-based emission inventory, Multi-scale Emission Inventory for China (MEIC), was compiled and used to drive the Community Atmosphere Model Version 5 (CAM5) to evaluate aerosol distribution and radiative effects in China against observations, compared with the model simulations with the widely-used IPCC AR5 emission inventory. We found that the new MEIC emission improves the annual mean AOD simulations in eastern China by 12.9 % compared with MODIS observations and 14.7 % compared with MISR observations, and explains 22 %–28 % of the AOD low bias simulated with the AR5 emission. Seasonal variation of the MEIC emission leads to a better agreement with the observed surface concentrations of primary aerosols (i.e., primary organic carbon and black carbon) than the AR5 emission, while the seasonal variation of secondary aerosols (i.e., sulfate and secondary organic aerosol) depends less on the emission. The new emission inventory estimates the annual averaged aerosol direct radiative effect at TOA, surface, and atmosphere to be −0.50, −12.76, and 12.26 W m−2 respectively over eastern China, which are enhanced by −0.19, −2.42, and 2.23 W m−2 compared with the AR5 emission. Due to higher winter BC emission in MEIC, the atmospheric warming effect and the surface cooling of BC are twice as much as those using the AR5 emission. This study highlights the importance of improving the aerosol and gas precursor emissions in modeling the atmospheric aerosols and their radiative effects.

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