Equatorial Warming Research Articles

Equatorward shift of the boreal summer intertropical convergence zone in Maritime Continent and the impacts on surface black carbon concentration and public health

In Maritime Continent, the shift of intertropical convergence zone (ITCZ) location directly regulates the distribution of black carbon and hence affects public health in the region, but the mechanism and human health impacts have not yet been comprehensively revealed. Here we used multiple reanalysis datasets to investigate the long-term shift of seasonal-mean zonal-mean ITCZ location in this region from 1980 to 2014, and to assess the influences on black carbon distribution and the resultant health impact in terms of premature mortality. Results show that recent human-related equatorial warming contributed to an equatorward shift (∼2.1°) of ITCZ location in Maritime Continent. Spatially, the equatorward shift of ITCZ reduced surface black carbon concentration over the maritime area by enhancing updrafts and wet deposition, but raised the concentration in the continental area by inhibiting updrafts. Meanwhile, anomalous low-level northeasterlies weakened summer circulation and prevented black carbon from being transported to the Philippines. Our results also suggest that the equatorward shift decreased ∼13% of black carbon-associated monthly premature mortality in maritime countries, but increased ∼6% of that in continental countries based on the population and mortality rate in 2010. We therefore recommend considering climate change impacts in the design of adaptation strategies against regional air pollution.

Boosting effect of strong western pole of the Indian Ocean Dipole on the decay of El Niño events

The Indian Ocean Basin (IOB) mode is believed to favor the decay of El Niño via modulating the zonal wind anomalies in the western equatorial Pacific, while the contribution of the Indian Ocean Dipole (IOD) mode to the following year’s El Niño remains highly controversial. In this study, we use the evolution of fast and slow decaying El Niño events during 1950–2020 to demonstrate that the positive IOD with a strong western pole prompts the termination of El Niño, whereas a weak western pole has no significant effect. The strong western pole of a positive IOD leads to a strong IOB pattern peaking in the late winter (earlier than normal), enhancing local convection and causing anomalous rising motions over the tropical Indian Ocean and sinking motions over the western tropical Pacific. The surface equatorial easterly wind anomalies on the western flank of the sinking motions stimulate oceanic equatorial upwelling Kelvin waves, which shoal the thermocline in the eastern equatorial Pacific and rapidly terminate the equatorial warming during El Niño. However, a weak western pole of the IOD induces a weak IOB mode that peaks in the late spring, and the above-mentioned cross-basin physical processes do not occur.

The Effect of an Exponentially Decaying Upper-Ocean Vertical Mixing on the Pacific Tropical Sea Surface Temperature

Abstract We investigate the mechanisms with which the sea surface temperature (SST) in the tropical Pacific responds to the perturbation of an exponential form to the background vertical mixing of the upper ocean. For a surface value of 0.005 m2 s−1 and a scale depth of 10 m (as typically used in the so-called nonbreaking wave parameterization), it is found that only ocean temperature within the equatorial eastern Pacific (EEP) is directly impacted; surface cooling and thermocline warming anomalies are produced. These signals propagate poleward as coastal Kelvin waves and then westward as equatorial Rossby waves. The surface cooling is severely damped while the thermocline warming is able to reach the western coast. This warm anomaly is brought up to the surface by equatorial upwelling more strongly around 110°W than at other places. In the coupled model, such equatorial warming induces an El Niño–like large-scale warming through Bjerknes feedback. Increasing the surface value of vertical mixing by a factor of 10 does not increase the equatorial surface warming while increasing the scale depth to 20 m does. Increasing the scale depth generates thermocline warming also in the subtropical region, which then propagates to the equatorial thermocline and enhances the warming there. Moreover, the off-equatorial cooling is enhanced, which makes the final warming anomaly narrower meridionally compared to an El Niño pattern.

Influencing factors associated with the second dominant pattern of the Indian summer monsoon

AbstractThe interannual variation of the Indian summer monsoon (ISM) affects millions of people in India and the global weather and climate. The teleconnections that affect this variation are not stable. The recent four decades of the second dominant mode of ISM rainfall show a unique north–south tripole pattern, with above‐normal rainfall in the north and peninsular India sandwiching suppressed rainfall in central‐east India. The pattern relates to extending the Indo‐Pacific warm‐pool's warmer sea‐surface temperature (SST) towards the south of the equatorial eastern Indian Ocean. Most of the time, this warming and the extension of the warm‐pool's warmer SST are associated with La Niña events, which activate more in situ vigorous convection. The Rossby‐gyres generated west of the equatorial heating increase the tropospheric height over north India, shifting and strengthening the Tibetan High northwards, facilitating heavy rainfall in the north. Meanwhile, the more vigorous convection south of the equatorial eastern Indian Ocean produces compensatory subsidence over central‐east India, suppressing rainfall. The northern hemispheric Rossby‐gyres brings anomalous cyclonic circulation over peninsular India, producing excess rainfall. Also, the dipole pressure anomaly between the northwest Pacific and south tropical Indian Ocean generates anomalous lower‐level easterly winds over the Bay of Bengal. It supplies excess moisture to the north India convections. The co‐occurrence of the active Atlantic intertropical convergence zone supports this tripole rainfall pattern. This teleconnection could further be examined in climate models.

The Effect of Tropical Pacific Air‐Sea Coupling on the Rainfall Response to Quadrupled CO2 Forcing

AbstractWe perform quadrupled CO2 climate simulations with the Community Earth System Model version 1 (CESM1) to study how air‐sea coupling affects the response of tropical rainfall under global warming. We use a hierarchy of ocean models to separate the effects of seasonal mixed‐layer entrainment, wind‐driven Ekman flows directed perpendicular to the wind, and the near‐equator frictional flows directed in the same direction as the wind. We show that the Pacific Ocean's enhanced equatorial warming pattern (EEW) and equatorward ITCZ contraction observed in previous climate simulations emerge when the ocean model includes wind‐driven Ekman and frictional flows. Furthermore, the near‐equator frictional flow contributes more than half of the heat convergence in the equatorial Pacific Ocean. Finally, we show that although Ekman flow and near‐equator frictional flow can both result in EEW, their coupled interactions with the Hadley circulation lead to opposite feedbacks on EEW's strength.

Rainfall and Salinity Effects on Future Pacific Climate Change

AbstractMost climate models simulate an intensified eastern equatorial Pacific warming in response to increasing greenhouse gas concentrations. So far, the proposed mechanisms have focused on thermodynamic aspects such as the spatial inhomogeneity of evaporative feedbacks, and future increases in upper ocean thermal stratification, partly intensified by projected Walker circulation weakening. Here we show, using earth system model freshwater perturbation experiments, that the simulated future rainfall intensification along the equator plays an important role in tropical climate change. Associated negative equatorial salinity anomalies of about −0.6 permil, which are very similar to the projected late 21st century salinity anomalies in CMIP6 SSP585 scenario, strengthen upper ocean stratification in the Pacific which leads to a flattening of the thermocline, shoaling of the equatorial undercurrent, and major shifts in tropical ocean dynamics. The resulting eastern basin equatorial warming also contributes to a marked weakening of the Pacific Walker circulation. Our analysis illustrates the importance of rainfall and salinity changes in the tropical climate system with relevance for understanding both, patterns of future climate change as well as the El Niño Southern Oscillation phenomenon.

Excitation of the Madden‐Julian Oscillation in Response to Transient Ocean Warming in SPCAM

AbstractRecent studies have suggested that the Madden‐Julian oscillation (MJO) could be generated as part of atmospheric adjustment to localized equatorial heating in models properly resolving moist convection. Here we use the Super‐parameterized Community Atmosphere Model (SPCAM) to study atmospheric response to transient sea surface warming in the equatorial Indian Ocean, which leads to the excitation of an MJO event, robust across different experiments, in addition to the expected equatorial Rossby and Kelvin waves. A moist static energy (MSE) budget analysis suggests that longwave and surface turbulent latent heat flux anomalies are predominantly responsible for the MJO excitation; however, these terms oppose its eastward propagation. In contrast, advection of MSE generally weakens the MJO amplitude, but contributes to its eastward propagation. These results highlight the role of the MJO in the moist atmospheric adjustment to localized tropical heating, with implications for the MJO mechanisms and prediction.

Western and Central Tropical Pacific Rainfall Response to Climate Change: Sensitivity to Projected Sea Surface Temperature Patterns

Abstract Rainfall projections from the Coupled Model Intercomparison Project (CMIP) models are strongly tied to projected sea surface temperature (SST) spatial patterns through the “warmer-gets-wetter” mechanism. While these models consistently project an enhanced equatorial warming, they, however, indicate much more uncertain changes in zonal SST gradients. That translates into large uncertainties on rainfall projections. Here, we force an atmospheric model with synthetic SSTs whose zonal SST gradient changes span the range of CMIP5 uncertainties in the presence and in the absence of the robust equatorially enhanced warming. Our results confirm that projected rainfall changes are dominated by the effect of circulation changes, which are tied to SST through the “warmer-gets-wetter” mechanism. We show that SPCZ rainfall changes are entirely driven by the uncertain zonal SST gradient changes. The western equatorial Pacific rainfall increase is largely controlled by the robust enhanced equatorial warming for modest zonal SST gradient changes. However, for larger values, the effect of the zonal SST gradient change on rainfall projections becomes dominant due to nonlinear interactions with the enhanced equatorial warming. Overall, our study demonstrates that uncertainties in the zonal SST gradient changes strongly contribute to uncertainties in rainfall projections over both the South Pacific convergence zone and western equatorial Pacific. It is thus critical to reduce these uncertainties to produce more robust precipitation estimates.

Seasonally and Regionally Dependent Shifts of the Atmospheric Westerly Jets under Global Warming

Abstract A distinct feature of the atmospheric circulation response to increasing greenhouse gas forcing is the poleward shift of the zonal-mean westerly jet. The dynamical mechanisms of the zonal-mean poleward jet shift have been extensively studied in literature. At seasonal/regional scales, however, the westerly jets can shift equatorward, such as in the early-summer Asia–Pacific region, the late-winter America–Atlantic region, and the winter/spring east Pacific. These equatorward jet shifts imply climate impacts distinct from those of the poleward shifts, yet their causes are not well understood. Here, based on a hierarchy of coupled, prescribed-SST, and aquaplanet simulations, we attribute the seasonal/regional equatorward jet shifts to the enhanced tropical upper-level warming (ETUW), which arises from both the tropical moist adiabat and the enhanced equatorial surface warming. By steepening the meridional temperature gradient in the subtropical upper-to-middle level and assisted by positive eddy feedback, the ETUW increases the zonal wind equatorward of the climatological jet. When the regional/seasonal meridional temperature gradients (or equivalently the westerly jets) are weak and peak close to the tropics, the ETUW effect overcomes the poleward jet-shift mechanisms and leads to the equatorward jet shifts. This climatological-state dependency is consistently seen in the decomposed jet responses to uniform warming and surface warming pattern, and further demonstrated through idealized aquaplanet experiments with designed climatological states. For uniform warming, the ETUW arising from moist adiabat makes the general poleward jet shifts insignificant in the aforementioned favorable regions/seasons. For warming pattern, the ETUW from enhanced equatorial warming drives substantial equatorward jet shifts in these favorable seasons/regions.

Correction to: Role of the eastern equatorial Indian Ocean warming in the Indian summer monsoon rainfall trend

Correction to: Role of the eastern equatorial Indian Ocean warming in the Indian summer monsoon rainfall trend

Global Warming Pattern Formation: The Role of Ocean Heat Uptake

Abstract This study investigates the formation mechanism of the ocean surface warming pattern in response to a doubling CO2 with a focus on the role of ocean heat uptake (or ocean surface heat flux change, ΔQnet). We demonstrate that the transient patterns of surface warming and rainfall change simulated by the dynamic ocean–atmosphere coupled model (DOM) can be reproduced by the equilibrium solutions of the slab ocean–atmosphere coupled model (SOM) simulations when forced with the DOM ΔQnet distribution. The SOM is then used as a diagnostic inverse modeling tool to decompose the CO2-induced thermodynamic warming effect and the ΔQnet (ocean heat uptake)–induced cooling effect. As ΔQnet is largely positive (i.e., downward into the ocean) in the subpolar oceans and weakly negative at the equator, its cooling effect is strongly polar amplified and opposes the CO2 warming, reducing the net warming response especially over Antarctica. For the same reason, the ΔQnet-induced cooling effect contributes significantly to the equatorially enhanced warming in all three ocean basins, while the CO2 warming effect plays a role in the equatorial warming of the eastern Pacific. The spatially varying component of ΔQnet, although globally averaged to zero, can effectively rectify and lead to decreased global mean surface temperature of a comparable magnitude as the global mean ΔQnet effect under transient climate change. Our study highlights the importance of air–sea interaction in the surface warming pattern formation and the key role of ocean heat uptake pattern.

The 2019 Benguela Niño

High interannual sea surface temperature anomalies of more than 2°C were recorded along the coasts of Angola and Namibia between October 2019 and January 2020. This extreme coastal warm event that has been classified as a Benguela Niño, reached its peak amplitude in November 2019 in the Angola Benguela front region. In contrast to classical Benguela Niños, the 2019 Benguela Niño was generated by a combination of local and remote forcing. In September 2019, a local warming was triggered by positive anomalies of near coastal wind-stress curl leading to downwelling anomalies through Ekman dynamics off Southern Angola and by anomalously weak winds reducing the latent heat loss by the ocean south of 15°S. In addition, downwelling coastal trapped waves were observed along the African coast between mid-October 2019 and early January 2020. Those coastal trapped waves might have partly emanated from the equatorial Atlantic as westerly wind anomalies were observed in the central and eastern equatorial Atlantic between end of September to early December 2019. Additional forcing for the downwelling coastal trapped waves likely resulted from an observed weakening of the prevailing coastal southerly winds along the Angolan coast north of 15°S between October 2019 and mid-February 2020. During the peak of the event, latent heat flux damped the sea surface temperature anomalies mostly in the Angola Benguela front region. In the eastern equatorial Atlantic, relaxation of cross-equatorial southerly winds might have contributed to the equatorial warming in November 2019 during the peak of the 2019 Benguela Niño. Moreover, for the first time, moored velocities off Angola (11°S) revealed a coherent poleward flow in the upper 100 m in October and November 2019 suggesting a contribution of meridional heat advection to the near-surface warming during the early stages of the Benguela Niño. During the Benguela Niño, a reduction of net primary production in the Southern Angola and Angola Benguela front regions was observed.

Excitation of the Madden–Julian Oscillation in Atmospheric Adjustment to Equatorial Heating

AbstractWe study the adjustment of the tropical atmosphere to localized surface heating using a Lagrangian atmospheric model (LAM) that simulates a realistic Madden–Julian oscillation (MJO)—the dominant, eastward-propagating mode of tropical intraseasonal variability modulating atmospheric convection. Idealized warm sea surface temperature (SST) anomalies of different aspect ratios and magnitudes are imposed in the equatorial Indian Ocean during MJO-neutral conditions and then maintained for 15 days. The experiments then continue for several more months. Throughout these experiments, we observe a robust generation of an MJO event, evident in precipitation, velocity, temperature, and moisture fields, which becomes a key element of atmospheric adjustment along with the expected Kelvin and Rossby waves. The MJO circulation pattern gradually builds up during the first week, and then starts to propagate eastward at a speed of 5–7 m s−1. The upper-level quadrupole circulation characteristic of the MJO becomes evident around day 14, with two anticyclonic gyres generated by the Gill-type response to convective heating and two cyclonic gyres forced by the excited Kelvin waves and extratropical Rossby wave trains. A moisture budget analysis shows that the eastward propagation of the MJO is controlled largely by the anomalous advection of moisture and by the residual between anomalous moisture accumulation due to converging winds and precipitation. The initial MJO event is followed by successive secondary events, maintaining the MJO for several more cycles. Thus, this study highlights the fundamental role that the MJO can play in the adjustment of the moist equatorial atmosphere to localized surface heating.

A Model Study of the Role of Convection in Westerly Wind Burst Dynamics

AbstractWesterly wind bursts (WWBs) are anomalous surface wind gusts that play an important role in ENSO dynamics. Previous studies have identified several mechanisms that may be involved in the dynamics of WWBs. In particular, many have examined the importance of atmospheric deep convection to WWBs, including convection due to tropical cyclones, equatorial waves, and the Madden–Julian oscillation. Still, the WWB mechanism is not yet fully understood. In this study, we investigate the location of atmospheric convection which leads to WWBs and the role of positive feedbacks involving surface evaporation. We find that disabling surface flux feedbacks a few days before a WWB peaks does not weaken the event, arguing against local surface flux feedbacks serving as a WWB growth mechanism on individual events. On the other hand, directly suppressing convection by inhibiting latent heat release or eliminating surface evaporation rapidly weakens a WWB. By selectively suppressing convection near or farther away from the equator, we find that convection related to off-equatorial cyclonic vortices is most important to equatorial WWB winds, while on-equator convection is unimportant. Despite the strong resemblance of WWB wind patterns to the Gill response to equatorial heating, our findings indicate that equatorial convection is not necessary for WWBs to develop. Our conclusions are consistent with the idea that tropical cyclones, generally occurring more than 5° away from the equator, may be responsible for the majority of WWBs.

A stronger versus weaker Walker: understanding model differences in fast and slow tropical Pacific responses to global warming

The tropical Pacific response to radiative forcing remains uncertain as projected future changes to the Walker circulation and SST patterns vary substantially among climate models. Here, we study what sets the magnitude and timescales of the response and why they differ across models. Specifically, we compare the fast and slow responses of the tropical Pacific to abrupt CO2 increases (2, 4, 8, 16 × CO2) in two configurations of the same model family (CESM) that differ in horizontal resolution and mean biases. We find that the model with a higher resolution shows a transient ocean thermostat-like response to CO2-forcing, with a stronger Walker cell and lack of warming in the eastern Pacific trade wind belts. This fast response lasts for about 50 years and is followed by a slight Walker cell weakening and equatorial warming. The second model, with a coarser resolution, shows a weak and short-lasting ocean thermostat response, followed by pronounced Walker cell weakening and eastern equatorial Pacific warming, similar to the long-term pattern noted in previous studies. These fast and slow responses also manifest in experiments where CO2 is gradually increased. We relate the magnitude of the fast ocean-thermostat response to the structure of the equatorial thermocline, setting the strength of the Bjerknes feedback. The magnitude and timing of the delayed eastern equatorial Pacific warming are related to the competition of positive feedbacks amplifying the ocean thermostat against the effect of ocean subsurface warming eroding the thermostat. The latter effect is further amplified by the slowdown of oceanic subtropical cells and enhanced extra-tropical warming. Different balances between these effects could explain the large spread in the model future projections for the tropical Pacific.

Contrasting Recent and Future ITCZ Changes From Distinct Tropical Warming Patterns

AbstractThis study synthesizes the observed trends and projected changes in the Intertropical Convergence Zones (ITCZs). Under future warming, the seasonal ITCZs are projected to shift equatorward, widen, and weaken. The equatorward‐shifted seasonal ITCZs cause a squeeze of the annual‐mean zonal‐mean tropical ascent. Over 1979–2014, however, the seasonal ITCZs have shifted poleward in South Pacific and generally narrowed and strengthened. The observed annual‐mean zonal‐mean changes are largely opposite to the future squeeze. Such contrasting ITCZ changes are attributed to the distinct tropical warming patterns. Specifically, the equatorial Pacific has cooled following a phase change in the Pacific Decadal Oscillation (PDO) but will warm more than the tropics in future. The ITCZ response to tropical warming pattern is consistent with thermodynamic/energetic theories and demonstrated through SST‐forced experiments. In the coming decades, a positive PDO can act jointly with anthropogenically forced equatorial warming, leading to substantial ITCZ changes that are distinct from recent trends.

Strong remote control of future equatorial warming by off-equatorial forcing

The tropical climate response to GHG forcing is spatially non-uniform1–3. Even though enhanced equatorial and eastern Pacific warming is simulated by most climate models, the underlying mechanisms—including the relative roles of atmospheric and oceanic feedbacks—remain debated. Here, we use a climate model with idealized CO2-radiative forcing patterns to show that off-equatorial radiative forcing and corresponding coupled circulation/cloud adjustments are responsible for much of equatorial warming in response to global CO2 forcing. For equatorial forcing, the atmosphere responds by enhancing atmospheric heat export to the extra-tropics, an associated strengthening of the ascending Hadley circulation branch and strong negative equatorial cloud feedbacks. These processes together greatly dampen equatorial surface warming. Intensification of the oceanic subtropical cells and increased cold subsurface water upwelling in the eastern tropical Pacific provide an additional negative feedback for surface temperatures. In contrast, applying off-equatorial forcing, the atmosphere responds by exporting less heat from the tropics, Hadley circulation weakening and weaker negative equatorial cloud feedbacks, while the subtropical cells slow down in the ocean. Our results demonstrate a delicate balance in the coupled climate system between remote circulation adjustments and regional feedbacks that create the patterns of future climate change. The relative roles of local and remote processes in determining equatorial warming are still debated. Model simulations show that coupled feedbacks strongly damp the equatorial surface temperature response to local equatorial forcing, while amplifying the response to remote off-equatorial forcing.

Ocean Dynamics Shapes the Structure and Timing of Atlantic Equatorial Modes

AbstractA recent study has brought to light the co‐existence of two distinct Atlantic Equatorial Modes during negative phases of the Atlantic Multidecadal Variability: the Atlantic Niño and Horse‐Shoe (HS) mode. Nevertheless, the associated air‐sea interactions for HS mode have not been explored so far and the prevailing dynamic view of the Atlantic Niño has been questioned. Here, using a forced ocean model simulation, we find that for both modes, ocean dynamics is essential to explain the equatorial SST variations, while air‐sea fluxes control the off‐equatorial SST anomalies. Moreover, we demonstrate the key role played by ocean waves in shaping their distinct structure and timing. For the positive phase of both Atlantic Niño and HS, anomalous westerly winds trigger a set of equatorial downwelling Kelvin waves (KW) during spring‐summer. These dKWs deepen the thermocline, favouring the equatorial warming through vertical diffusion and horizontal advection. Remarkably, for the HS, an anomalous north‐equatorial wind stress curl excites an upwelling Rossby wave (RW), which propagates westward and is reflected at the western boundary becoming an equatorial upwelling KW. The uKW propagates to the east, activating the thermocline feedbacks responsible to cool the sea surface during summer months. This RW‐reflected mechanism acts as a negative feedback causing the early termination of the HS mode. Our results provide an improvement in the understanding of the TAV modes and emphasize the importance of ocean wave activity to modulate the equatorial SST variability. These findings could be very useful to improve the prediction of the Equatorial Modes.

Enhanced equatorial warming causes deep-tropical contraction and subtropical monsoon shift

Under anthropogenic warming, deep-tropical ascent of the intertropical convergence zone (ITCZ) is projected to contract equatorward1–3 while subtropical descent associated with the Hadley cell edge is predicted to expand poleward4. These changes have important implications for regional climate2,5–7, but their mechanisms are not well understood. Here we reveal a key role of enhanced equatorial surface warming (EEW) in driving the deep-tropical contraction and modulating the Hadley expansion. By shifting the seasonally warmed sea surface temperature equatorward, EEW reduces the meridional migration of the seasonal ITCZ and causes an annual-mean deep-tropical contraction. This process further contracts the subtropical circulation, as seen during El Nino, and counteracts the Hadley expansion caused by the global-scale warming. The EEW-induced contraction even dominates in the Northern Hemisphere early summer (June–July), when atmospheric circulation responses to the global-scale warming are weak8. Regionally, this alters the East Asian summer monsoon, shifting both the subtropical jet and Meiyu–Baiu rainband equatorward. Among models in Phase 5 of the Coupled Model Intercomparison Project9, the degrees of the equatorward shift in the ITCZ, the early-summer subtropical circulation and the East Asian summer monsoon are correlated with EEW. Our results suggest that a better constraint on EEW is critical for accurate projection of tropical and subtropical climate change. Global warming projections exhibit a contracted intertropical convergence zone (ITCZ) and an expanded Hadley cell. Here, equatorial Pacific warming is shown to contract seasonal ITCZ migration and counteract Hadley cell expansion, leading to an equatorward shift in the Asian subtropical monsoon.

Both differential and equatorial heating contributed to African monsoon variations during the mid-Holocene

The Sahara was significantly greener 11-5 kya and during multiple earlier interglacial periods. But the mechanisms related to the greening of the Sahara remain uncertain as most climate models severely underestimate past wet conditions over north Africa. The variations in the African monsoon related to the greening of the Sahara are thought to be associated with the variations in the inter-hemispheric differential heating of Earth, caused by orbital variations. However, how orbital variations affect regional climate is not well understood. Using recent theory that relates the position of the tropical rain belt to the atmospheric energy budget, we study the effect of orbital forcing during the mid-Holocene on the African monsoon in simulations provided by the third phase of the Paleo Model Intercomparison Project (PMIP3). We find that energy fluxes in the African sector are related to orbital forcing in a complex manner. Contrary to generally accepted theory, orbital modulation of seasonal differential heating alone is shown to be a weak driver of African monsoon variations. Instead, net atmospheric heating near the equator, which modulates the intensity and extent of seasonal migrations of the tropical rain belt, is an important but overlooked driver of African monsoon variations. A conceptual framework that relates African monsoon variations to both equatorial and inter-hemispheric differential solar heating is presented.