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 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.

The Hadley Circulation Regime Change: Combined Effect of the Western Pacific Warming and Increased ENSO Amplitude

2018 ◽  
Vol 31 (23) ◽  
pp. 9739-9751 ◽  
Author(s):  
Yi-Peng Guo ◽  
Zhe-Min Tan
Keyword(s):  
Regime Change ◽  
Southern Oscillation ◽  
Hadley Circulation ◽  
Warming Trend ◽  
Combined Effect ◽  
Western Pacific ◽  
South Pacific Convergence Zone ◽  
Boreal Winter ◽  
Enso Events

The variation in the interannual relationship between the boreal winter Hadley circulation (HC) and El Niño–Southern Oscillation (ENSO) during 1948–2014 is investigated. The interannual variability of the HC is dominated by two principal modes: the equatorial asymmetric mode (AM) and the equatorial symmetric mode (SM). The AM of the HC during ENSO events mainly results from a combined effect of the ENSO sea surface temperature (SST) anomalies and the climatological background SST over the South Pacific convergence zone. Comparatively, the SM shows a steady and statistically significant relationship with ENSO; however, the interannual relationship between the AM and ENSO is strengthened during the mid-1970s, which leads to a HC regime change—that is, the interannual pulse of the HC intensity and its response to ENSO are stronger after the mid-1970s than before. The long-term warming trend of the tropical western Pacific since the 1950s and the increased ENSO amplitude play vital roles in the HC regime change. Although the tropical eastern Pacific also experienced a long-term warming trend, it has little influence on the HC regime change due to the climatologically cold background SST over the cold tongue region.

Quasi-Biweekly Oscillation over the tropical western Pacific in boreal winter： Its climate influences on North America

2020 ◽  
Author(s):  
Zizhen Dong ◽  
Lin Wang
Keyword(s):  
North America ◽  
Energy Conversion ◽  
Rossby Wave ◽  
Time Scale ◽  
Wave Train ◽  
Western Pacific ◽  
Boreal Winter ◽  
The South ◽  
Tropical Western Pacific ◽  
South Of Japan

&lt;p&gt;&lt;span lang=&quot;EN-US&quot;&gt;The Quasi-Biweekly Oscillation (QBWO) mode with 10-20-day time scale over the tropical western Pacific (TWP) in boreal winter (December-February), characterized by westward-northwestward propagation from the dateline to the east coast of Philippines (EPH) identified by the first two EEOF modes, is investigated based on the daily mean OLR and ERA-Interim reanalysis datasets from 1979 to 2015. The suppressive (active) QBWO-related convection heating located near EPH at peak day (day 0), results in anomalous divergence (convergence) wind to the south of Japan at upper troposphere due to the heat release. The divergent circulations can advect climatological absolute vorticity, then leads to positive (negative) Rossby wave source, which could propagate eastward. Therefore, a Rossby wave train (RWT) with equivalent barotropical structure over Pacific originated from the south of Japan is observed one/two days later. This wave train propagates northeastward into Alaska and then southeastward into southern North America. The meridional wind associated with the cyclonic/anticyclonic anomalies of RWT advects climatological thermal condition dominating the local temperature tendency over North America. Thus, a significant warming (cooling) over central North America is found at day +4 consistent to the anomalous southerlies (northerlies). In addition, both the barotropical energy conversion (CK) and baroclinic energy conversion (CP) contribute to the RWT on a time scale of 10-20 days maintained against dissipation.&lt;/span&gt;&lt;/p&gt;

Idealized Simulations of the Intertropical Convergence Zone and Its Multilevel Flows

2010 ◽  
Vol 67 (12) ◽  
pp. 4028-4053 ◽  
Author(s):  
David S. Nolan ◽  
Scott W. Powell ◽  
Chidong Zhang ◽  
Brian E. Mapes
Keyword(s):  
Surface Temperature ◽  
Dynamic Instability ◽  
Vertical Motion ◽  
Sea Breeze ◽  
Return Flow ◽  
Eddy Fluxes ◽  
Convergence Zones ◽  
Upper Level ◽  
Static Energy ◽  
Regional Budgets

Abstract A mesoscale numerical model with an idealized tropical channel environment is used to study the dynamics of intertropical convergence zones (ITCZs) and the recently identified shallow return flow (SRF) and midlevel inflow (MLI). Four idealized sea surface temperature (SST) distributions are used: a meridionally symmetric SST profile with a sharply peaked SST maximum at the equator, a similar profile with the maximum SST shifted off the equator, a cosine-shaped SST profile with zero gradient at the equator, and an idealized SST profile modeled after the observed SST of the eastern Pacific. The simulations show that both the SRF and the MLI are robust features of the ITCZ. The prior result that the SRF is a sea-breeze-like response to surface temperature gradients is further supported, whereas the MLI is caused by the upper-level maxima in diabatic heating and vertical motion. Simulations with the SST maximum at the equator generate long-lasting, convectively coupled Kelvin waves. When the SST maximum is off the equator, the meridional circulations become highly asymmetric with strong cross-equatorial flow. Tropical cyclones are frequently generated by dynamic instability of the off-equatorial ITCZs. The contributions of the multilevel circulations to regional budgets of mass, water, and moist static energy (MSE) are computed. About 10% of the total water transported into the ITCZ region is transported out by the SRF. The water transport of the MLI is minimal, but its mass and MSE transports are significant, accounting for about ⅓ of the mass and MSE entering the ITCZ region. Eddy fluxes are found to be a large component of the net vertically integrated transport of MSE out of the ITCZ.

scholarly journals Seasonal Modulations of the Active MJO Cycle Characterized by Nonlinear Principal Component Analysis

2011 ◽  
Vol 139 (7) ◽  
pp. 2259-2275 ◽  
Author(s):  
Johannes Jenkner ◽  
William W. Hsieh ◽  
Alex J. Cannon
Keyword(s):  
Longwave Radiation ◽  
Principal Component ◽  
Boreal Winter ◽  
Convective Activity ◽  
Marginal Contributions ◽  
The Indian Ocean ◽  
The Mean ◽  
The Difference ◽  
Upper Level ◽  
Mean Cycle

Abstract A novel methodology is presented for the identification of the mean cycle of the Madden–Julian oscillation (MJO) along the equator. The methodology is based on a nonlinear principal component (NLPC) computed with a neural network model. The bandpass-filtered input data encompass 30 yr with zonal winds at 850 and 200 hPa plus outgoing longwave radiation (OLR). The NLPC is conditioned on a sufficiently strong MJO activity and is computed both for the pooled dataset and for the dataset stratified into seasons. The NLPC for all data depicts a circular mode formed by the first two linear principal components (LPCs) with marginal contributions by the higher-order LPCs. Hence, the mean MJO cycle throughout the year is effectively captured by the amplitude of the leading two LPCs varying in quadrature. The NLPC for individual seasons shows additional variability, which mainly arises from a subordinate oscillation of the second pair of LPCs superimposed on the annual MJO signal. In reference to the all-year solution, the difference in resolved variability approximately accounts for 9% in solstitial seasons and 3% in equinoctial seasons. The phasing of the third LPC is such that convective activity oscillations over the Maritime Continent as well as wind oscillations over the Indian Ocean appear enhanced (suppressed) during boreal winter (summer). Also, convective activity oscillations appear more pronounced at the date line during both winter and summer. The phasing of the fourth LPC is such that upper-level westerlies over the Atlantic region are more persistent during boreal spring than during other seasons.

scholarly journals Energetic Constraints on the Width of the Intertropical Convergence Zone

2016 ◽  
Vol 29 (13) ◽  
pp. 4709-4721 ◽  
Author(s):  
Michael P. Byrne ◽  
Tapio Schneider
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Hadley Circulation ◽  
Intertropical Convergence Zone ◽  
Future Climate Change ◽  
Convergence Zone ◽  
Moist Static Energy ◽  
Wide Range ◽  
Gross Moist Stability ◽  
Static Energy

Abstract The intertropical convergence zone (ITCZ) has been the focus of considerable research in recent years, with much of this work concerned with how the latitude of maximum tropical precipitation responds to natural climate variability and to radiative forcing. The width of the ITCZ, however, has received little attention despite its importance for regional climate and for understanding the general circulation of the atmosphere. This paper investigates the ITCZ width in simulations with an idealized general circulation model over a wide range of climates. The ITCZ, defined as the tropical region where there is time-mean ascent, displays rich behavior as the climate varies, widening with warming in cool climates, narrowing in temperate climates, and maintaining a relatively constant width in hot climates. The mass and energy budgets of the Hadley circulation are used to derive expressions for the area of the ITCZ relative to the area of the neighboring descent region, and for the sensitivity of the ITCZ area to changes in climate. The ITCZ width depends primarily on four quantities: the net energy input to the tropical atmosphere, the advection of moist static energy by the Hadley circulation, the transport of moist static energy by transient eddies, and the gross moist stability. Different processes are important for the ITCZ width in different climates, with changes in gross moist stability generally having a weak influence relative to the other processes. The results are likely to be useful for analyzing the ITCZ width in complex climate models and for understanding past and future climate change in the tropics.

scholarly journals Initialized Decadal Predictions by LASG/IAP Climate System Model FGOALS-s2: Evaluations of Strengths and Weaknesses

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Bo Wu ◽  
Xiaolong Chen ◽  
Fengfei Song ◽  
Yong Sun ◽  
Tianjun Zhou
Keyword(s):  
Indian Ocean ◽  
Radiative Forcing ◽  
Climate Model ◽  
Initial Conditions ◽  
Global Climate Model ◽  
Western Pacific ◽  
Decadal Prediction ◽  
Climate System Model ◽  
Tropical Western Pacific ◽  
The Indian Ocean

Decadal prediction experiments are conducted by using the coupled global climate model FGOALS-s2, following the CMIP 5 protocol. The paper documents the initialization procedures for the decadal prediction experiments and summarizes the predictive skills of the experiments, which are assessed through indicators adopted by the IPCC AR5. The observational anomalies of surface and subsurface ocean temperature and salinity are assimilated through a modified incremental analysis update (IAU) scheme. Three sets of 10-year-long hindcast and forecast runs were started every five years in the period of 1960–2005, with the initial conditions taken from the assimilation runs. The decadal prediction experiment by FGOALS-s2 shows significant high predictive skills in the Indian Ocean, tropical western Pacific, and Atlantic, similar to the results of the CMIP5 multimodel ensemble. The predictive skills in the Indian Ocean and tropical western Pacific are primarily attributed to the model response to the external radiative forcing associated with the change of atmospheric compositions. In contrast, the high skills in the Atlantic are attributed, at least partly, to the improvements in the prediction of the Atlantic multidecadal variability coming from the initialization.

scholarly journals Tropical atmospheric circulation response to the G1 sunshade geoengineering radiative forcing experiment

2018 ◽  
Vol 18 (12) ◽  
pp. 8689-8706 ◽  
Author(s):  
Anboyu Guo ◽  
John C. Moore ◽  
Duoying Ji
Keyword(s):  
Radiative Forcing ◽  
Hadley Circulation ◽  
Walker Circulation ◽  
Static Stability ◽  
Solar Radiation Management ◽  
Management Scenario ◽  
The Difference ◽  
Radiation Management ◽  
Different Response ◽  
The Walker Circulation

Abstract. We investigate the multi-Earth system model response of the Walker circulation and Hadley circulations under the idealized solar radiation management scenario (G1) and under abrupt4xCO2. The Walker circulation multi-model ensemble mean shows changes in some regions but no significant change in intensity under G1, while it shows a 4∘ eastward movement and 1.9 × 109 kg s−1 intensity decrease in abrupt4xCO2. Variation in the Walker circulation intensity has the same high correlation with sea surface temperature gradient between the eastern and western Pacific under both G1 and abrupt4xCO2. The Hadley circulation shows significant differences in behavior between G1 and abrupt4xCO2, with intensity reductions in the seasonal maximum northern and southern cells under G1 correlated with equatorward motion of the Intertropical Convergence Zone (ITCZ). Southern and northern cells have a significantly different response, especially under abrupt4xCO2 when impacts on the southern Ferrel cell are particularly clear. The southern cell is about 3 % stronger under abrupt4xCO2 in July, August and September than under piControl, while the northern is reduced by 2 % in January, February and March. Both circulations are reduced under G1. There are significant relationships between northern cell intensity and land temperatures, but not for the southern cell. Changes in the meridional temperature gradients account for changes in Hadley intensity better than changes in static stability in G1 and especially in abrupt4xCO2. The difference in the response of the zonal Walker circulation and the meridional Hadley circulations under the idealized forcings may be driven by the zonal symmetric relative cooling of the tropics under G1.

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