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 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.

scholarly journals How Does El Niño Affect the Interannual Variability of the Boreal Summer Hadley Circulation?

2014 ◽  
Vol 27 (7) ◽  
pp. 2622-2642 ◽  
Author(s):  
Yong Sun ◽  
Tianjun Zhou
Keyword(s):  
Interannual Variability ◽  
El Niño ◽  
El Nino ◽  
Asian Summer Monsoon ◽  
Hadley Circulation ◽  
Department Of Energy ◽  
Hadley Cell ◽  
Boreal Summer ◽  
Interannual Variations ◽  
Sst Forcing

Abstract Analyses of 30-yr four reanalysis datasets [NCEP–NCAR reanalysis (NCEP1), NCEP–Department of Energy reanalysis (NCEP2), Japanese 25-year Reanalysis Project (JRA-25), and Interim ECMWF Re-Analysis (ERA-Interim)] reveal remarkably interannual variability of the Hadley circulation (HC) in boreal summer (June–August). The two leading modes of interannual variability of boreal summer HC are obtained by performing empirical orthogonal function (EOF) analysis on the mass streamfunction. A general intensification of boreal summer HC is seen in EOF-1 mode among NCEP1, NCEP2, and JRA-25 but the corresponding EOF-2 mode in ERA-Interim, while a weakened northern Hadley cell and remarkable regional variation of a southern Hadley cell are captured by the EOF-2 mode (from NCEP1, NCEP2, and JRA-25) and EOF-1 mode (from ERA-Interim), as evidenced by the enhanced (decreased) southern Hadley cell in the southern tropics (the northern tropics and southern subtropics). Both modes are driven by El Niño–like SST forcing in boreal summer, but are relevant to different phases of El Niño events. The EOF-1 (or EOF-2 derived from ERA-Interim) [EOF-2 (or EOF-1 derived from ERA-Interim)] mode is driven by SST anomalies in developing (decaying) El Niño summers. The interannual variations of the northern Hadley cell in both modes are driven by El Niño through modulating the interannual variations of the East Asian summer monsoon, while anomalous local Hadley circulation (LHC) in the regions 30°S–20°N, 110°E–180° and 30°S–20°N, 160°E–120°W in response to El Niño forcing largely determine the interannual variations of southern Hadley cell in both modes, respectively. The different behaviors of the southern Hadley cell between two leading modes can be well explained by the southward shift of the tropical heating center from north of 10°N in developing El Niño summers to south of 10°N in decaying El Niño summers.

scholarly journals Global Monsoon Precipitation: Trends, Leading Modes, and Associated Drought and Heat Wave in the Northern Hemisphere

2018 ◽  
Vol 31 (17) ◽  
pp. 6947-6966 ◽  
Author(s):  
Kaiqiang Deng ◽  
Song Yang ◽  
Mingfang Ting ◽  
Yaheng Tan ◽  
Shan He
Keyword(s):  
Northern Hemisphere ◽  
El Niño ◽  
El Nino ◽  
Boreal Summer ◽  
Soil Conditions ◽  
Monsoon Precipitation ◽  
Central Pacific ◽  
Global Monsoon ◽  
Cp El Niño ◽  
Ep El Niño

Global monsoon precipitation (GMP) brings the majority of water for the local agriculture and ecosystem. The Northern Hemisphere (NH) GMP shows an upward trend over the past decades, while the trend in the Southern Hemisphere (SH) GMP is weak and insignificant. The first three singular value decomposition modes between NH GMP and global SST during boreal summer reflect, in order, the Atlantic multidecadal oscillation (AMO), eastern Pacific (EP) El Niño, and central Pacific (CP) El Niño, when the AMO dominates the NH climate and contributes to the increased trend. However, the first three modes between SH GMP and global SST during boreal winter are revealed as EP El Niño, the AMO, and CP El Niño, when the EP El Niño becomes the most significant driver of the SH GMP, and the AMO-induced rainfall anomalies may cancel out each other within the SH global monsoon domain and thus result in a weak trend. The intensification of NH GMP is proposed to favor the occurrences of droughts and heat waves (HWs) in the midlatitudes through a monsoon–desert-like mechanism. That is, the diabatic heating associated with the monsoonal rainfall may drive large-scale circulation anomalies and trigger intensified subsidence in remote regions. The anomalous descending motions over the midlatitudes are usually accompanied by clear skies, which result in less precipitation and more downward solar radiation, and thus drier and hotter soil conditions that favor the occurrences of droughts and HWs. In comparison, the SH GMP may exert much smaller impacts on the NH extremes in spring and summer, probably because the winter signals associated with SH GMP cannot sufficiently persist into the following seasons.

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 Contrasting terrestrial carbon cycle responses to the two strongest El Niño events: 1997–98 and 2015–16 El Niños

2017 ◽  
Author(s):  
Jun Wang ◽  
Ning Zeng ◽  
Meirong Wang ◽  
Fei Jiang ◽  
Hengmao Wang ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Northern Hemisphere ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Carbon Cycle Model ◽  
Geographical Regions ◽  
El Niño Events ◽  
The Tropics ◽  
El Nino Events

Abstract. The large interannual CO2 variability is dominated by the response of terrestrial biosphere to El Niño-Southern Oscillation (ENSO). However, behaviors of terrestrial ecosystems differ in patterns and biological processes in different El Niño events. Here we conduct a comprehensive comparison of the two strongest El Niño events in history, namely, the recent 2015–16 event, and the earlier 1997–98 event in the context of multi-event composite El Niño. We analyze Mauna Loa CO2 concentration, surface carbon fluxes from three atmospheric inversions, and a mechanistic carbon cycle model VEGAS. We find large differences in the carbon cycle responses, even though the two El Nino events are of similar magnitude. We find that the land-atmosphere carbon flux (FTA) anomaly in 1997–98 El Niño was 1.95 Pg C yr–1 globally, but two times smaller during 2015–16 El Niño at 0.79 Pg C yr–1. We also find that FTA had no obvious lagged response in 2015–16 El Niño, in contrast to that in 1997–98 El Niño. Separating the global flux by major geographical regions, during 1997–98, the fluxes in the tropics and extratropical northern hemisphere were 1.98 and 0.04 Pg C yr–1, respectively. During 2015–16, these were 1.07 and 0.4 Pg C yr–1. Analysis of the mechanism shows that in the tropics, the widespread drier and warmer conditions caused the decrease in gross primary productivity (GPP, 1.11 Pg C yr–1) and increase in terrestrial ecosystem respiration (TER, 0.49 Pg C yr–1) in 1997–98 El Niño. During 2015–16, in contrast, anomalously wet conditions occurred in Sahel and East Africa that caused increase in GPP, compensating its decrease over other tropical regions. As a result, the total 2015–16 tropical GPP and TER anomalies were 0.29 and 1.23 Pg C yr–1. GPP dominance during 1997–98 and TER dominance during 2015–16 accounted for the phase difference in their FTA. In extratropical northern hemisphere, we find that temperature was warmer both in 1997–98 and 2015–16 El Niños over North America, contributing to enhancements in GPP and TER. However, temperature over Eurasia was warmer in 2015–16 El Niño, opposing to the cooler in 1997–98 and composite El Niño events. This warmer condition enhanced GPP and TER over the Eurasia in 2015–16 El Niño, compared to their suppressions in 1997–98 El Niño. The total extratropical northern hemisphere GPP and TER anomalies were 0.86 and 0.74 Pg C yr–1 in 1997–98 El Niño and 1.8 and 1.47 Pg C yr–1 in 2015–16 El Niño. Additionally, we find that wildfires played less important roles in 2015–16 El Niño than in 1997–98 El Niño.

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.

scholarly journals ENSO’s Impact on the Gap Wind Regions of the Eastern Tropical Pacific Ocean*

2012 ◽  
Vol 25 (10) ◽  
pp. 3549-3565 ◽  
Author(s):  
Michael A. Alexander ◽  
Hyodae Seo ◽  
Shang Ping Xie ◽  
James D. Scott
Keyword(s):  
Pacific Ocean ◽  
Boundary Conditions ◽  
El Niño ◽  
El Nino ◽  
Tropical Pacific ◽  
Surface Fluxes ◽  
Ocean Dynamics ◽  
Tropical Pacific Ocean ◽  
Variable Surface ◽  
Sst Anomalies

Abstract The recently released NCEP Climate Forecast System Reanalysis (CFSR) is used to examine the response to ENSO in the northeast tropical Pacific Ocean (NETP) during 1979–2009. The normally cool Pacific sea surface temperatures (SSTs) associated with wind jets through the gaps in the Central American mountains at Tehuantepec, Papagayo, and Panama are substantially warmer (colder) than the surrounding ocean during El Niño (La Niña) events. Ocean dynamics generate the ENSO-related SST anomalies in the gap wind regions as the surface fluxes damp the SSTs anomalies, while the Ekman heat transport is generally in quadrature with the anomalies. The ENSO-driven warming is associated with large-scale deepening of the thermocline; with the cold thermocline water at greater depths during El Niño in the NETP, it is less likely to be vertically mixed to the surface, particularly in the gap wind regions where the thermocline is normally very close to the surface. The thermocline deepening is enhanced to the south of the Costa Rica Dome in the Papagayo region, which contributes to the local ENSO-driven SST anomalies. The NETP thermocline changes are due to coastal Kelvin waves that initiate westward-propagating Rossby waves, and possibly ocean eddies, rather than by local Ekman pumping. These findings were confirmed with regional ocean model experiments: only integrations that included interannually varying ocean boundary conditions were able to simulate the thermocline deepening and localized warming in the NETP during El Niño events; the simulation with variable surface fluxes, but boundary conditions that repeated the seasonal cycle, did not.

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 The relationship between intraseasonal tropical variability and ENSO and its modulation at seasonal to decadal timescales

2011 ◽  
Vol 3 (2) ◽  
Author(s):  
Daria Gushchina ◽  
Boris Dewitte
Keyword(s):  
El Niño ◽  
General Circulation ◽  
Rossby Waves ◽  
El Nino ◽  
General Circulation Models ◽  
Wave Radiation ◽  
Boreal Summer ◽  
Central Pacific ◽  
Tropical Variability ◽  
Intraseasonal Tropical Variability

AbstractThe intraseasonal tropical variability (ITV) patterns in the tropical troposphere are documented using double space-time Fourier analysis. Madden and Julian oscillations (MJO) as well as equatorial coupled waves (Kelvin and Rossby) are investigated based on the NCEP/NCAR Reanalysis data for the 1977–2006 period and the outputs of an intermediate ocean-atmosphere coupled model named LODCA-OTCM. A strong seasonal dependence of the ITV/ENSO relationship is evidenced. The leading relationship for equatorial Rossby waves (with the correlation of the same order than for the MJO) is documented; namely, it is shown that intensification of Rossby waves in the central Pacific during boreal summer precedes by half a year the peak of El Niño. The fact that MJO activity in spring-summer is associated to the strength of subsequent El Niño is confirmed. It is shown that LODCA-QTCM is capable of simulating the convectively coupled equatorial waves in outgoing long wave radiation and zonal wind at 850 hPa fields with skill comparable to other Coupled General Circulation Models. The ITV/ENSO relationship is modulated at low frequency. In particular the periods of low ENSO amplitude are associated with weaker MJO activity and a cancellation of MJO at the ENSO development phase. In opposition, during the decaying phase, MJO signal is strong. The periods of strong ENSO activity are associated with a marked coupling between MJO, Kelvin and equatorially Rossby waves and ENSO; the precursor signal of MJO (Rossby waves) in the western (central) Pacific is obvious. The results provide material for the observed change in ENSO characteristics in recent years and question whether the characteristics of the ITV/ENSO relationship may be sensitive to the observed warming in the central tropical Pacific.

scholarly journals Diagnosis of Tropospheric Moisture over Saudi Arabia and Influences of IOD and ENSO

2006 ◽  
Vol 134 (2) ◽  
pp. 598-617 ◽  
Author(s):  
Arun Chakraborty ◽  
Swadhin K. Behera ◽  
Milind Mujumdar ◽  
Ryohji Ohba ◽  
Toshio Yamagata
Keyword(s):  
Saudi Arabia ◽  
Correlation Coefficient ◽  
Red Sea ◽  
El Niño ◽  
El Nino ◽  
Moisture Flux ◽  
Boreal Summer ◽  
Atmospheric Moisture ◽  
Middle Troposphere ◽  
Peak Correlation

Abstract A diagnostic study of atmospheric moisture data over Saudi Arabia derived from a 43-yr National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis revealed that moisture convergence in the lower troposphere and divergence in and above the middle troposphere occurs throughout the year. Although the amount of precipitable water content in the middle troposphere is high, precipitation is less than expected over this semiarid region during a boreal summer monsoon season because of strong moisture divergence. The net tropospheric moisture flux over the arid and semiarid regions of Saudi Arabia shows seasonal and interannual variability. The seasonal variability has a strong semiannual signal with its primary peak February–April and its secondary peak June–August. This pattern is consistent with a similar semiannual signal observed in rainfall climatology. The restricted moisture supply to southwestern Saudi Arabia during summer presumably explains the lack of precipitation in other areas of the country. Winter precipitation, however, is widespread. The increased transport of net atmospheric moisture flux is higher during El Niño and positive Indian Ocean dipole (IOD) phenomena. During these events, influx across the Red Sea (west) side of Saudi Arabia increases. The net flux to the region is reduced by a slight increase of outflux across the Persian Gulf (east) side. Reanalysis data and model-sensitivity experiments show that El Niño or a concurrent positive IOD and El Niño event more strongly amplify net transport than does an independent positive IOD event. The partial-lag correlation analysis with net moisture flux from the Red Sea side shows that the positive IOD mode has a peak correlation coefficient of ∼0.5 with close to a 5-month lead and that El Niño has a peak correlation coefficient of ∼0.6 with close to a 2-month lead.

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