scholarly journals Unprecedented strength of Hadley circulation in 2015–2016 impacts on CO<sub>2</sub> interhemispheric difference

2018 ◽  
Author(s):  
Jorgen S. Frederiksen ◽  
Roger J. Francey
Keyword(s):  
Global Warming ◽  
Hadley Circulation ◽  
Co2 Concentration ◽  
Transport Processes ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Advective Transport ◽  
Interhemispheric Difference ◽  
Eddy Transport ◽  
The Difference

Abstract. The extreme El Niño of 2015 and 2016 coincided with record global warming and unprecedented strength of the Hadley circulation with significant impact on mean interhemispheric (IH) transport of CO2 and on the difference in CO2 concentration between Mauna Loa and Cape Grim (Cmlo-cgo). The relative roles of eddy transport and mean advective transport on IH CO2 annual differences from 1992 through to 2016 is explored. Eddy transport processes occur mainly in boreal winter-spring when Cmlo-cgo is large; an important component is due to Rossby wave generation by the Himalayas and propagation through the equatorial Pacific westerly duct generating and transmitting turbulent kinetic energy. Mean transport occurs mainly in boreal summer-autumn and varies with the strength of the Hadley circulation. The timing of annual changes in Cmlo-cgo is found to coincide well with dynamical indices that we introduce to characterize the transports. During the unrivalled 2009–2010 step in Cmlo-cgo indices of eddy and mean transport reinforce. In contrast for the 2015 to 2016 change in Cmlo-cgo the mean transport counteracts the eddy transport and the record strength of the Hadley circulation determines the annual IH CO2 difference. The interaction of increasing global warming and extreme El Niños may have important implications for altering the balance between eddy and mean IH CO2 transfer.

scholarly journals Unprecedented strength of Hadley circulation in 2015–2016 impacts on CO<sub>2</sub> interhemispheric difference

2018 ◽  
Vol 18 (20) ◽  
pp. 14837-14850 ◽  
Author(s):  
Jorgen S. Frederiksen ◽  
Roger J. Francey
Keyword(s):  
Global Warming ◽  
Hadley Circulation ◽  
Co2 Concentration ◽  
Transport Processes ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Advective Transport ◽  
Mauna Loa ◽  
Interhemispheric Difference ◽  
Eddy Transport

Abstract. The extreme El Niño of 2015 and 2016 coincided with record global warming and unprecedented strength of the Hadley circulation with significant impact on mean interhemispheric (IH) transport of CO2. The relative roles of eddy transport and mean advective transport on interannual differences in CO2 concentration between Mauna Loa and Cape Grim (Cmlo−cgo), from 1992 through to 2016, are explored. Eddy transport processes occur mainly in boreal winter–spring when Cmlo−cgo is large; an important component is due to Rossby wave generation by the Himalayas and propagation through the equatorial Pacific westerly duct generating and transmitting turbulent kinetic energy. Mean transport occurs mainly in boreal summer–autumn and varies with the strength of the Hadley circulation. The timing of annual changes in Cmlo−cgo is found to coincide well with dynamical indices that we introduce to characterize the transport. During the unrivalled 2009–2010 step in Cmlo−cgo, the effects of the eddy and mean transport were reinforced. In contrast, for the 2015 to 2016 change in Cmlo−cgo, the mean transport counteracts the eddy transport and the record strength of the Hadley circulation determines the annual IH CO2 difference. The interaction of increasing global warming and extreme El Niños may have important implications for altering the balance between eddy and mean IH CO2 transfer. The effects of interannual changes in mean and eddy transport on interhemispheric gradients in other trace gases are also examined.

scholarly journals Changes of the Boreal Winter Hadley Circulation in the NCEP–NCAR and ECMWF Reanalyses: A Comparative Study

2007 ◽  
Vol 20 (20) ◽  
pp. 5191-5200 ◽  
Author(s):  
Hua Song ◽  
Minghua Zhang
Keyword(s):  
Radiative Forcing ◽  
Atmospheric Transport ◽  
Vertical Motion ◽  
Hadley Circulation ◽  
Western Pacific ◽  
Boreal Winter ◽  
Tropical Western Pacific ◽  
The Difference ◽  
Upper Level ◽  
Static Energy

Abstract Both the ECMWF and the NCEP–NCAR reanalyses show a strengthening of the atmospheric Hadley circulation in boreal winter over the last 50 years, but the intensification is much stronger in the ECMWF than in the NCEP–NCAR reanalysis. This study focuses on the difference of these trends in the two reanalyses. It is shown that trends in the Hadley circulation in the two reanalyses differ mainly over the tropical western Pacific. This difference is found to be consistent with respective trends of the atmospheric transport of moist static energy, longwave cloud radiative forcing, and upper-level clouds in the two reanalyses. Two independent datasets of upper-level cloud cover and sea level pressure from ship-based measurements are then used to evaluate the reanalyses over the tropical western Pacific. They are found to be more consistent with the trends in the NCEP–NCAR reanalysis than those in the ECMWF reanalysis. The results suggest a weakening of the vertical motion associated with the Hadley circulation in the tropical western Pacific.

scholarly journals Variability in a four-network composite of atmospheric CO<sub>2</sub> differences between three primary baseline sites

2019 ◽  
Author(s):  
Roger J. Francey ◽  
Jorgen S. Frederiksen ◽  
L. Paul Steele ◽  
Ray L. Langenfelds
Keyword(s):  
Northern Hemisphere ◽  
Hadley Circulation ◽  
Enso Event ◽  
Surface Fluxes ◽  
Boreal Summer ◽  
Monitoring Networks ◽  
Carbon Cycle Model ◽  
Co2 Partial Pressure ◽  
Interhemispheric Difference ◽  
Order Of Magnitude

Abstract. Spatial differences in the monthly baseline CO2 since 1992 from Mauna Loa, (mlo, 19.5° N, 155.6° W, 3379 m), Cape Grim (cgo, 40.7° S, 144.7° E, 94 m) and South Pole (spo, 90° S, 2810 m), are examined for consistency between four monitoring networks. For each site pair, a composite based on the average of NOAA, CSIRO and two independent SIO analysis methods is presented. Averages of the monthly standard deviations are 0.25, 0.23 and 0.16 ppm for mlo-cgo, mlo-spo and cgo-spo respectively. This high degree of consistency and near-monthly temporal differentiation (compared to CO2 growth rates) provides an opportunity to use the composite differences for verification of global carbon cycle model simulations. Interhemispheric CO2 variation is predominantly imparted by the mlo data. The peaks and dips of the seasonal variation in interhemispheric difference act largely independently. The peaks mainly occur in May, near the peak of Northern Hemisphere terrestrial respiration. Boreal spring is when interhemispheric exchange via eddy processes dominates, with increasing contributions from mean transport into boreal summer. The dips occur in September, when the CO2 partial pressure difference is near zero, just after the peak in the mean interhemispheric exchange via the Hadley circulation. Surface-air terrestrial flux anomalies would need to be up to an order of magnitude larger than found in order to explain the peak and dip CO2 variations (large enough to significantly influence short-term northern hemisphere growth rate variations). Recent features in the composite records, inconsistent in timing and amplitude with air-surface fluxes, are largely consistent with interhemispheric transport variations. These include the remarkable stability in annual CO2 inter-hemispheric difference in the 5-year relatively ENSO-quiet period 2010–2014, and the 2017 recovery in the CO2 interhemispheric gradient from the unprecedented ENSO event in 2015–16.

Hemispherical Asymmetry of Tropical Precipitation in ECHAM5/MPI-OM during El Niño and under Global Warming

2008 ◽  
Vol 21 (6) ◽  
pp. 1309-1332 ◽  
Author(s):  
Chia Chou ◽  
Jien-Yi Tu
Keyword(s):  
Global Warming ◽  
El Niño ◽  
El Nino ◽  
Hadley Circulation ◽  
Seasonal Migration ◽  
Boreal Summer ◽  
Max Planck ◽  
Tropical Precipitation ◽  
Precipitation Anomalies ◽  
Precipitation Changes

Abstract Similarities and differences between El Niño and global warming are examined in hemispherical and zonal tropical precipitation changes of the ECHAM5/Max Planck Institute Ocean Model (MPI-OM) simulations. Similarities include hemispherical asymmetry of tropical precipitation changes. This precipitation asymmetry varies with season. In the boreal summer and autumn (winter and spring), positive precipitation anomalies are found over the Northern (Southern) Hemisphere and negative precipitation anomalies are found over the Southern (Northern) Hemisphere. This precipitation asymmetry in both the El Niño and global warming cases is associated with the seasonal migration of the Hadley circulation; however, their causes are different. In El Niño, a meridional moisture gradient between convective and subsidence regions is the fundamental basis for inducing the asymmetry. Over the ascending branch of the Hadley circulation, convection is enhanced by less effective static stability. Over the margins of the ascending branch, convection is suppressed by the import of dry air from the descending branch. In global warming, low-level moisture is enhanced significantly due to warmer tropospheric temperatures. This enhances vertical moisture transport over the ascending branch of the Hadley circulation, so convection is strengthened. Over the descending branch, the mean Hadley circulation tends to transport relatively drier air downward, so convection is reduced.

scholarly journals Heavy Precipitation Events in a Warmer Climate: Results from CMIP5 Models

2013 ◽  
Vol 26 (20) ◽  
pp. 7902-7911 ◽  
Author(s):  
Enrico Scoccimarro ◽  
Silvio Gualdi ◽  
Alessio Bellucci ◽  
Matteo Zampieri ◽  
Antonio Navarra
Keyword(s):  
Heavy Precipitation ◽  
First Century ◽  
Cmip5 Models ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Precipitation Distribution ◽  
Twenty First Century ◽  
The Difference ◽  
The Right ◽  
Precipitation Events

Abstract In this work, the authors investigate possible changes in the distribution of heavy precipitation events under a warmer climate, using the results of a set of 20 climate models taking part in phase 5 of Coupled Model Intercomparison Project (CMIP5). Future changes are evaluated as the difference between the last four decades of the twenty-first century and the twentieth century, assuming the representative concentration pathway 8.5 (RCP8.5) scenario. As a measure of the width of the right tail of the precipitation distribution, the authors use the difference between the 99th and the 90th percentiles. Despite a slight tendency to underestimate the observed heavy precipitation, the considered CMIP5 models well represent the observed patterns in terms of the ensemble average, during both boreal summer and winter seasons for the 1997–2005 period. Future changes in average precipitation are consistent with previous findings based on models from phase 3 of CMIP (CMIP3). CMIP5 models show a projected increase for the end of the twenty-first century of the width of the right tail of the precipitation distribution, particularly pronounced over India, Southeast Asia, Indonesia, and central Africa during boreal summer, as well as over South America and southern Africa during boreal winter.

scholarly journals Variability in a four-network composite of atmospheric CO<sub>2</sub> differences between three primary baseline sites

2019 ◽  
Vol 19 (23) ◽  
pp. 14741-14754
Author(s):  
Roger J. Francey ◽  
Jorgen S. Frederiksen ◽  
L. Paul Steele ◽  
Ray L. Langenfelds
Keyword(s):  
Northern Hemisphere ◽  
El Niño ◽  
El Nino ◽  
Hadley Circulation ◽  
Surface Fluxes ◽  
Boreal Summer ◽  
Monitoring Networks ◽  
Carbon Cycle Model ◽  
Co2 Partial Pressure ◽  
Interhemispheric Difference

Abstract. Spatial differences in the monthly baseline CO2 since 1992 from Mauna Loa (mlo, 19.5∘ N, 155.6∘ W, 3379 m), Cape Grim (cgo, 40.7∘ S, 144.7∘ E, 94 m), and South Pole (spo, 90∘ S, 2810 m) are examined for consistency between four monitoring networks. For each site pair, a composite based on the average of NOAA, CSIRO, and two independent Scripps Institution of Oceanography (SIO) analysis methods is presented. Averages of the monthly standard deviations are 0.25, 0.23, and 0.16 ppm for mlo–cgo, mlo–spo, and cgo–spo respectively. This high degree of consistency and near-monthly temporal differentiation (compared to CO2 growth rates) provide an opportunity to use the composite differences for verification of global carbon cycle model simulations. Interhemispheric CO2 variation is predominantly imparted by the mlo data. The peaks and dips of the seasonal variation in interhemispheric difference act largely independently. The peaks mainly occur in May, near the peak of Northern Hemisphere (NH) terrestrial photosynthesis/respiration cycle. February–April is when interhemispheric exchange via eddy processes dominates, with increasing contributions from mean transport via the Hadley circulation into boreal summer (May–July). The dips occur in September, when the CO2 partial pressure difference is near zero. The cross-equatorial flux variation is large and sufficient to significantly influence short-term Northern Hemisphere growth rate variations. However, surface–air terrestrial flux anomalies would need to be up to an order of magnitude larger than found to explain the peak and dip CO2 difference variations. Features throughout the composite CO2 difference records are inconsistent in timing and amplitude with air–surface fluxes but are largely consistent with interhemispheric transport variations. These include greater variability prior to 2010 compared to the remarkable stability in annual CO2 interhemispheric difference in the 5-year relatively El Niño-quiet period 2010–2014 (despite a strong La Niña in 2011), and the 2017 recovery in the CO2 interhemispheric gradient from the unprecedented El Niño event in 2015–2016.

scholarly journals The Atmospheric Response to a Thermohaline Circulation Collapse: Scaling Relations for the Hadley Circulation and the Response in a Coupled Climate Model

2010 ◽  
Vol 23 (3) ◽  
pp. 757-774 ◽  
Author(s):  
Sybren S. Drijfhout
Keyword(s):  
Thermohaline Circulation ◽  
Climate Model ◽  
Baroclinic Instability ◽  
Hadley Circulation ◽  
Relative Strength ◽  
Hadley Cell ◽  
Boreal Summer ◽  
Coupled Climate Model ◽  
The Difference ◽  
Hadley Cells

Abstract The response of the tropical atmosphere to a collapse of the thermohaline circulation (THC) is investigated by comparing two 5-member ensemble runs with a coupled climate model (CCM), the difference being that in one ensemble a hosing experiment was performed. An extension of the Held–Hou–Lindzen model for the Hadley circulation is developed to interpret the results. The forcing associated with a THC collapse is qualitatively similar to, but smaller in amplitude than, the solstitial shift from boreal summer to winter. This forcing results from reduced ocean heat transport creating an anomalous cross-equatorial SST gradient. The small amplitude of the forcing makes it possible to arrive at analytical expressions using standard perturbation theory. The theory predicts the latitudinal shift between the Northern Hemisphere (NH) and Southern Hemisphere (SH) Hadley cells, and the relative strength of the anomalous cross-equatorial Hadley cell compared to the solstitial cell. The poleward extent of the Hadley cells is controlled by other physics. In the NH the Hadley cell contracts, while zonal velocities increase and the subtropical jet shifts equatorward, whereas in the SH cell the opposite occurs. This behavior can be explained by assuming that the poleward extent of the Hadley cell is determined by baroclinic instability: it scales with the inverse of the isentropic slopes. Both theory and CCM results indicate that a THC collapse and changes in tropical circulation do not act in competition, as a possible explanation for abrupt climate change; they act in concert.

scholarly journals A Global Tropical Survey of Mid-Tropospheric Cyclones

2021 ◽  
Author(s):  
Pradeep Kushwaha ◽  
Jai Sukhatme ◽  
Ravi Nanjundiah
Keyword(s):  
Temperature Anomaly ◽  
Central Africa ◽  
Lower Troposphere ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Natural Tendency ◽  
West And Central Africa ◽  
The Difference ◽  
The Tropics ◽  
Cold Core

AbstractMid-Tropospheric Cyclones (MTCs) are moist synoptic systems with distinct mid-tropospheric vorticity maxima and weak signatures in the lower troposphere. Composites and statistics of tropical MTCs are constructed and compared with monsoon lows and depressions (together, lower troposphere cyclones; LTCs). We begin with South Asia, where tracking reveals that MTCs change character during their life, i.e., their track is composed of MTC and LTC phases. The highest MTC-phase density and least motion is over the Arabian Sea, followed by the Bay of Bengal and the South China Sea. An MTC-phase composite shows an east-west tilted warm above deep cold-core temperature anomaly with maximum vorticity at 600 hPa. In contrast, the LTC-phase shows a shallow cold-core below 800 hPa and a warm upright temperature anomaly with a lower tropospheric vorticity maximum. Globally, systems with MTC-like morphology are observed over the west and central Africa, east and west Pacific in boreal summer. In boreal winter, regions that support MTCs include northern Australia, the southern Indian Ocean, and South Africa. MTC fraction is higher equatorward where there is a cross-equatorial low-level jet that advects oppositely signed vorticity. Whereas LTCs are more prevalent further poleward. Finally, a histogram of differential vorticity (the difference between middle and lower levels) versus the height of peak vorticity for cyclonic centers is shown to be bimodal. One peak, around 600 hPa, corresponds to MTCs, while the second, at approximately 900 hPa, comes from LTCs. Thus, moist cyclonic systems in the tropics have a natural tendency to reside in either the MTC or LTC category.

scholarly journals Atlantic Niño/Niña Prediction Skills in NMME Models

Atmosphere ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 803
Author(s):  
Ran Wang ◽  
Lin Chen ◽  
Tim Li ◽  
Jing-Jia Luo
Keyword(s):  
Sea Surface ◽  
Prediction Skill ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Equatorial Atlantic ◽  
Multimodel Ensemble ◽  
Spring Predictability Barrier ◽  
Anomaly Correlation Coefficient ◽  
Earth’S Climate ◽  
Atlantic Niño

The Atlantic Niño/Niña, one of the dominant interannual variability in the equatorial Atlantic, exerts prominent influence on the Earth’s climate, but its prediction skill shown previously was unsatisfactory and limited to two to three months. By diagnosing the recently released North American Multimodel Ensemble (NMME) models, we find that the Atlantic Niño/Niña prediction skills are improved, with the multi-model ensemble (MME) reaching five months. The prediction skills are season-dependent. Specifically, they show a marked dip in boreal spring, suggesting that the Atlantic Niño/Niña prediction suffers a “spring predictability barrier” like ENSO. The prediction skill is higher for Atlantic Niña than for Atlantic Niño, and better in the developing phase than in the decaying phase. The amplitude bias of the Atlantic Niño/Niña is primarily attributed to the amplitude bias in the annual cycle of the equatorial sea surface temperature (SST). The anomaly correlation coefficient scores of the Atlantic Niño/Niña, to a large extent, depend on the prediction skill of the Niño3.4 index in the preceding boreal winter, implying that the precedent ENSO may greatly affect the development of Atlantic Niño/Niña in the following boreal summer.

scholarly journals Changes in Spread and Predictability Associated with ENSO in an Ensemble Coupled GCM

2006 ◽  
Vol 19 (17) ◽  
pp. 4378-4396 ◽  
Author(s):  
Renguang Wu ◽  
Ben P. Kirtman
Keyword(s):  
Surface Pressure ◽  
El Niño ◽  
El Nino ◽  
Tropical Pacific ◽  
La Niña ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Central Pacific ◽  
La Nina ◽  
Signal Change

Abstract The present study documents the influence of El Niño and La Niña events on the spread and predictability of rainfall, surface pressure, and 500-hPa geopotential height, and contrasts the relative contribution of signal and noise changes to the predictability change based on a long-term integration of an interactive ensemble coupled general circulation model. It is found that the pattern of the El Niño–Southern Oscillation (ENSO)-induced noise change for rainfall follows closely that of the corresponding signal change in most of the tropical regions. The noise for tropical Pacific surface pressure is larger (smaller) in regions of lower (higher) mean pressure. The ENSO-induced noise change for 500-hPa height displays smaller spatial scales compared to and has no systematic relationship with the signal change. The predictability for tropical rainfall and surface pressure displays obvious contrasts between the summer and winter over the Bay of Bengal, the western North Pacific, and the tropical southwestern Indian Ocean. The predictability for tropical 500-hPa height is higher in boreal summer than in boreal winter. In the equatorial central Pacific, the predictability for rainfall is much higher in La Niña years than in El Niño years. This occurs because of a larger percent reduction in the amplitude of noise compared to the percent decrease in the magnitude of signal from El Niño to La Niña years. A consistent change is seen in the predictability for surface pressure near the date line. In the western North and South Pacific, the predictability for boreal winter rainfall is higher in El Niño years than in La Niña years. This is mainly due to a stronger signal in El Niño years compared to La Niña years. The predictability for 500-hPa height increases over most of the Tropics in El Niño years. Over western tropical Pacific–Australia and East Asia, the predictability for boreal winter surface pressure and 500-hPa height is higher in El Niño years than in La Niña years. The predictability change for 500-hPa height is primarily due to the signal change.

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