Haijun Yang

• Doctor of Philosophy
• Professor at Fudan University

The North Atlantic Oscillation (NAO), the dominant mode of atmospheric variability in the North Atlantic region, plays a crucial role in weather and climate. Here, to investigate when the NAO emerged and how it evolved over geological timescales, we analyzed time-slice paleoclimate simulations during the breakup of the supercontinent Pangea, starti...

The Atlantic Multidecadal Oscillation (AMO) has garnered attention for its important role in shaping surface air temperature (SAT) patterns over Eurasia. While Eurasian winter SAT was traditionally attributed to changes in large-scale atmospheric circulations associated with the AMO, a careful examination of the latest unforced CMIP6 simulations in...

Using a CESM1 control simulation, we conduct a follow-up study to advance our earlier theoretical research on the multicentennial oscillation (MCO) of the Atlantic meridional overturning circulation (AMOC). The modeled AMOC MCO primarily arises from internal oceanic processes in the North Atlantic, potentially representing a North Atlantic Ocean-or...

The meridional overturning circulation (MOC) in the ocean is a key player in the global climate system, while continental topography provides an essential backdrop to the system. In this study, we design a series of coupled model sensitivity experiments to investigate the influence of various mountain ranges on the global thermohaline circulation....

In the first part of our research on self-sustained multicentennial oscillation of the Atlantic meridional overturning circulation (AMOC), we utilized a hemispheric box model considering only the salinity equations. In this study, we consider both thermal and saline processes in the box model, to investigate the AMOC multicentennial oscillation and...

A significant multi-centennial climate variability with a distinct peak at approximately 200 years is observed in a pre-industrial (PI) control simulation using the EC-Earth3-LR climate model. This oscillation originates predominately from the North Atlantic and displays a strong association with the Atlantic Meridional Overturning Circulation (AMO...

The mid-Holocene (MH) is the most recent typical climate period and a subject of great interest in global paleocultural research. Following the latest Paleoclimate Modeling Intercomparison Project phase 4 (PMIP4) protocol and using a fully coupled climate model, we simulated the climate during both the MH and the preindustrial (PI) periods and quan...

The mid-Holocene (MH) is the most recent typical climate period and a subject of great interest in global pa-leocultural research. Following the latest Paleoclimate Mod-eling Intercomparison Project phase 4 (PMIP4) protocol and using a fully coupled climate model, we simulated the climate during both the MH and the preindustrial (PI) periods and qu...

The Tibetan Plateau (TP) impacts local and remote atmospheric circulations, wherein it mechanically and thermally affects air masses or airflows. Moreover, the TP provides a key channel for substance transport between the troposphere and the stratosphere. This study reviews recent advances in research regarding land–atmosphere coupling processes ov...

The role of the Tibetan Plateau (TP) in Asian hydrological climate is crucial, yet there is a lack of quantitative estimates regarding its impact on snowfall in China. Some opinions suggest that the TP functions as a large barrier that obstructs cold outbreaks, protecting southern China from severe snowstorms. Through topography experiments with an...

Previous studies have established a theory for self-sustained multicentennial oscillation (MCO) of the Atlantic Meridional Overturning Circulation (AMOC) in a one-hemisphere box model. In this paper, we extend this theory to the global scale and identify the similar self-sustained MCO of AMOC in a more realistic two-hemisphere box model. There are...

Long-term proxy data have suggested that there exists multi-centennial climate variability in the Earth’s climate system. The origin and mechanism of this variability have bewildered climatologists and archaeologists. From the mid-Holocene to pre-industrial time, the variation of external forcing of the Earth’ climate was relatively small; therefor...

The effect of the Tibetan Plateau (TP) on the Intertropical Convergence Zone (ITCZ) was investigated using a coupled Earth system model. The location of the ITCZ (in this work represented by the center of the tropical precipitation maximum) over the tropical Atlantic was found to be sensitive to the existence of the TP. Removing the TP led to a rem...

A central Pacific (CP) El Niño event occurred in 2018/19. Previous studies have shown that different mechanisms are responsible for different subtypes of CP El Niño events (CP-I El Niño and CP-II El Niño). By comparing the evolutions of surface winds, ocean temperatures, and heat budgets of the CP-I El Niño, CP-II El Niño, and 2018/19 El Niño, it i...

As the highest and most extensive plateau in the world, the Tibetan Plateau (TP) has remarkable effects on global climate. Through coupled model’s sensitivity experiments with and without the TP, we show that the TP can affect the Arctic directly via orography-forced stationary waves, and influence the Antarctic indirectly via stationary waves forc...

The unique characteristics of land–air coupling and troposphere–stratosphere interaction over the Tibetan Plateau (TP), the highest landform in the world, play a vital role in weather and climate on regional and global scales. Although a great deal of research has been carried out, large gaps remain in our understanding of TP land–air coupling and...

Variability on centennial to multi-centennial timescales is mentioned as a feature in reconstructions of the Holocene climate. As more long transient model simulations with complex climate models become available and efforts have been made to compile large proxy databases, there is now a unique opportunity to study multi-centennial variability with...

In this study, the influence of the Tibetan Plateau and the Rocky Mountains on ENSO variability is investigated using a fully coupled climate model. Compared to that in the real world, the amplitude of ENSO variability becomes larger after removing the Tibetan Plateau or the Rocky Mountains. The ENSO amplitude is considerably stronger in a world wi...

In this work, a single-hemisphere 4-box model is used to study the low-frequency variability of the Atlantic meridional overturning circulation (AMOC). We introduce an enhanced mixing mechanism in the subpolar ocean to balance the positive salinity advection feedback, so that the AMOC in the 4-box model exhibits a self-sustained multi-centennial os...

Despite the rapid increase of greenhouse gases (GHGs) in the atmosphere during the past 50 years, observed global mean surface temperature (GMST) showed a pause in the warming trend during the first decade of the twenty-first century. This is referred to as the global warming “hiatus”. A dominant hypothesis emphasizes that the superimposition of th...

Plain Language Summary The Tibetan Plateau (TP) plays a vital role in regulating the regional and global climate. By far, most studies focus on the impacts of TP thermal effect on atmospheric change. Few efforts have been devoted to investigate the TP thermal effect on ocean circulation. In this study, we artificially reduce and increase the surfac...

The Earth climate system has an intrinsic mechanism to maintain its energy conservation by impelling opposite changes in meridional ocean and atmosphere heat transports. This mechanism is briefed as the Bjerknes compensation (BJC). We set up a global coupled two-hemisphere box model in this study, and obtain an analytical solution to the BJC of thi...

It has been well known that the uplift of the Tibetan Plateau (TP) can significantly enhance the Asian monsoon. Here, by comparing the sensitivity experiments with and without the TP, we find that the TP uplift can also increase the precipitation of the North American Summer Monsoon (NASM), with atmosphere teleconnection accounting for 6% and ocean...

The Tibetan Plateau (TP) plays an important role in regulating the global hydrologic cycle. Using a fully coupled climate model, we conduct sensitivity experiments to quantify the impact of the TP on North Africa precipitation. Removing the TP in the model can enhance North African precipitation. Specifically, North Africa precipitation increases s...

The effect of the Rocky Mountains (RM) on meridional overturning circulations (MOCs) is investigated using a fully coupled climate model. Located between the Atlantic and Pacific oceans, the RM is the major mountains in North America. It presence plays an important role in atmospheric moisture transport between the two oceans. Adding the RM to a fl...

The Tibetan Plateau (TP) plays a vital role in shaping global climate. So far, however, few studies have focused on the impact of the TP on Southern Ocean (SO) circulation. Through fully coupled model experiments with and without the TP, we find that removing the TP could eventually enhance Antarctic bottom water (AABW) circulation by generating Ro...

The role of the Tibetan Plateau (TP) in El Niño-Southern Oscillation (ENSO) variability is investigated using coupled model experiments with different topography setup. Removing the TP results in weakened trade winds in the tropical Pacific, an eastward shift of atmospheric convection center, a shallower mixed layer in the equatorial Pacific, and a...

This paper reviews recent advances regarding land–atmosphere–ocean coupling associated with the Tibetan Plateau (TP) and its climatic impacts. Thermal forcing over the TP interacts strongly with that over the Iranian Plateau, forming a coupled heating system that elevates the tropopause, generates a monsoonal meridional circulation over South Asia...

The effects of the Tibetan Plateau (TP) on the Pacific Ocean circulation are investigated using a fully coupled climate model. Sensitivity experiments are designed to demonstrate that the presence of the TP is the reason for the lack of strong deep-water formation in the subpolar North Pacific, because removing the TP in the model would enable the...

The Tibetan Plateau (TP) over the Eurasian continent has significant effects on both regional and global climate. It can even affect the remote Atlantic meridional overturning circulation (AMOC), as confirmed in this study. Through coupled modeling experiments, we demonstrate that removing the TP immediately weakens the meridional wind over East As...

As the most extensive highland in the world, the Tibetan Plateau (TP) plays an important role in shaping the global climate. Quantifying the effect of the TP on global climate is the first step for a full understanding of TP’s standing on the planet Earth. Through coupled model sensitivity experiments, we draw a panorama of TP’s global impact in th...

The global temperature changes under global warming result from two effects: one is the pure radiative heating effect caused by a change in greenhouse gases, and the other is the freshwater effect related to changes in precipitation, evaporation, and sea ice. The two effects are separated in a coupled climate model through sensitivity experiments i...

The Bjerknes compensation (BJC) under global warming is studied using a simple box model and a coupled Earth systemmodel. The BJC states the out-of-phase changes in the meridional atmosphere and ocean heat transports. Results suggest that the BJC can occur during the transient period of global warming.During the transient period, the sea ice meltin...

The roles of energy balance and climate feedback in Bjerknes compensation (BJC) are studied through wind-perturbation experiments in a coupled climate model. Shutting down surface winds over the ocean causes significant reductions in both wind-driven and thermohaline overturning circulations, leading to a remarkable decrease in poleward ocean heat...

Using a coupled Earth climate model, freshwater forcing experiments are performed to study the Bjerknes compensation (BJC) between meridional atmosphere heat transport (AHT) and meridional ocean heat transport (OHT). Freshwater hosing in the North Atlantic weakens the Atlantic meridional overturning circulation (AMOC) and thus reduces the northward...

Effects of wind and fresh water on the Atlantic meridional overturning circulation (AMOC) are investigated using a fully coupled climate model. The AMOC can change significantly when perturbed by either wind stress or freshwater flux in the North Atlantic. This study focuses on wind stress effect. Our model results show that the wind forcing is cru...

The Bjerknes compensation (BJC) refers to the tendency for changes in the atmosphere heat transport (AHT) and ocean heat transport (OHT) to compensate each other. However, the nature of this compensation varies with the timescale of changes. In this study, we developed a new approach to diagnose BJC for climate variability, by considering the corre...

A coupled box model is used to study the compensation between atmosphere and ocean heat transports. An analytical solution to the Bjerknes compensation (BJC) rate, defined as the ratio of anomalous atmosphere heat transport (AHT) to anomalous ocean heat transport (OHT), is obtained. The BJC rate is determined by local feedback between surface tempe...

The response of the atmospheric energy (heat) transport (AHT) to a perturbation oceanic heat transport (OHT) is studied theoretically in a zonal mean energy balance model, with the focus on the effect of climate feedback, especially its spatial variation, on Bjerknes compensation (BJC). It is found that the BJC depends critically on climate feedbac...

The Earth's climate has experienced dramatic changes over the past 22,000 years; however, the total meridional heat transport (MHT) of the climate system remains stable. A 22,000-year-long simulation using an ocean-atmosphere coupled model shows that the changes in atmosphere and ocean MHT are significant but tend to be out of phase in most regions...

The effect of the ocean surface winds on the meridional heat transports is studied in a coupled model. Shutting down the global surface winds causes significant reductions in both wind-driven and thermohaline ocean circulations, resulting in a remarkable decrease in the poleward oceanic heat transport (OHT). The sea surface temperature responds wit...

The meridional heat transport (MHT) in the climate system is investigated using a state-of-the-art coupled climate model (CESM1.0). This work decomposes the MHT and studies their physics in detail. The meridional ocean heat transport (OHT) can be decomposed into the contributions from the Euler mean circulation, bolus circulation, sub-mesoscale cir...

The equatorial response to subtropical Pacific forcing was studied in a coupled climate model. The forcings in the western, central and eastern subtropical Pacific all caused a significant response in the equatorial thermocline, with comparable magnitudes. This work highlights the key role of air-sea coupling in the subtropical impact on the equato...

The mechanisms involved in the variability of Atlantic Meridional Overturning Circulation (AMOC) are studied using a 2000-yr control simulation of the coupled Fast Ocean-Atmosphere Model (FOAM). This study identifies a coupled mode between SST and surface heat flux in the North Atlantic at the decadal timescale, as well as a forcing mode of surface...

Using a fully coupled climate model, the impact of subtropical Pacific sea surface temperature anomalies (SSTA) at different longitude bands on the equatorial Pacific is quantitatively studied. Both equatorial SST responses and equatorial thermocline responses to the western, central, and eastern subtropical Pacific (20°-30°N) SSTA are comparable....

A B S T R A C T The compensation between the meridional heat transports in the atmosphere and ocean is studied through a coupled model's water-hosing experiments. It is found that the atmospheric heat transport (AHT) change compensates the oceanic heat transport (OHT) change very well in the extratropics, while the former over-compensates the latte...

Assessing the meridional atmosphere and ocean energy transport is one of the most classical problems in climate research. The meridional energy transport plays a critical role in maintaining the equilibrium of the earth system. Although the principle to calculate the meridional energy transport is simple, many fundamental questions remain unsolved....

In this paper, the dynamic effect of oceanic upwelling on the intensity of El Niño-Southern Oscillation (ENSO) is studied using a simple coupled model (Zebiak-Cane Model). The term balance analysis in the temperature variability equation shows that the anomalous upwelling of the mean vertical temperature gradient and the mean advection of the anoma...

The tropical oceanic response to the extratropical thermal forcing is quantitatively estimated in a coupled climate model. This work focuses on comparison of the responses between the tropical Atlantic and Pacific. Under the same extratropical forcing, the tropical sea surface temperature responses are comparable. However, the responses in the trop...

The equilibrium response timescale of global oceans is estimated in a fully coupled climate model. In general, the equilibrium timescale increases with depth, except in the polar region. The timescale is approximately 200 years for the ocean for depths above 1 km, and it increases to 1500 years at a depth of 3 km. A layer with a rapid timescale cha...

The thermocline depth is defined as the depth of the maximum vertical temperature gradient. In the equatorial Pacific, the depth of 20°C isotherm is widely used to represent the thermocline depth. This work proposes that under the circumstance of a significant mean climate shift, it is better to use the original definition of the thermocline depth...

The response mechanisms of the tropical Pacific Ocean temperature to increased atmospheric CO2 are investigated in a coupled climate model. Ensemble simulations are performed under both the transient and stable CO2 forcing. It is found that the dominant mechanism for temperature change differs in different stages of global warming. During the trans...

The response mechanisms of the tropical Pacific Ocean temperature to increased atmospheric CO 2 are investigated in a coupled climate model. Ensemble simulations are performed under both the transient and stable CO 2 forcing. It is found that the dominant mechanism for temperature change differs in different stages of global warming. During the tra...

A revisit on observations shows that the tropical El Niño–Southern Oscillation (ENSO) variability, after removing both the long-term trend and decadal variation of the background climate, has been enhanced by as much as 50% during the past 50 yr. This is inconsistent with the changes in the equatorial atmosphere, which shows a slowdown of the zonal...

1] The nonlinear response of the tropical ocean to the extratropical forcing is quantitatively estimated using a coupled climate model. Preliminary results based on sensitivity experiments show that the tropical response attributed to nonlinear processes is less than 10% of the linear response for annual mean climatology. This occurs mainly because...

Observations show that the tropical El Niño-Southern Oscillation (ENSO) variability, after removing both the long term trend and decadal change of the background climate, has been enhanced by as much as 60% during the past 50 years. This shift in ENSO amplitude can be related to mean state changes in global climate. Past global warming has caused a...

A coupled climate model is used to explore the response of the tropical sea surface temperature (SST) to positive SST anomalies in the global extratropics. The main model results here are consistent with previous numerical studies. In response to prescribed SST anomalies in the extratropics, the tropical SSTs rise rapidly and reach a quasi-equilibr...

Extratropical impacts on the tropical El Niño–Southern Oscillation (ENSO) are studied in a coupled climate model. Idealized experiments show that the remote impact of the extratropics on the equatorial thermocline through oceanic tunnel can substantially modulate the ENSO in both magnitude and frequency. First of all, an extratropical warming can b...

Tropical–extratropical climate interactions are studied by idealized experiments with a prescribed 2°C SST anomaly at different latitude bands in a coupled climate model. Instead of focusing on intrinsic climate variability, this work investigates the mean climate adjustment to remote external forcing. The extratropical impact on tropical climate c...

1] Idealized experiments in a coupled climate model show that the remote impact of the extratropics on the tropics can modulate the behavior of El Niño-Southern Oscillation (ENSO) phenomenon. An extratropical warming can weaken the Hadley cells and slow down the shallow meridional overturning circulations in the upper Pacific, causing reductions in...

Oceanic response to stochastic wind forcing is studied in a tropical–extratropical basin using two shallow water models: a periodically forced model and a time-forward model. Consistent with theory, extratropical stochastic wind forces a decadal spectral peak in the tropical and eastern boundary ocean as a resonant response of the planetary wave ba...

ABSTRACT The equatorial thermocline variability in the Pacific in response to the extratropical thermal and wind forcings is investigated with an ocean general circulation model [Modular Ocean Model, version 3 (MOM3)]. Sensitivity experiments,show,that the extratropical wind,forcing and thermal forcing contribute equally to the equatorial variabili...

The full spectrum of basin modes in a tropical-extratropical basin is studied comprehensively in a linear shallow-water system. Two sets of least-damped basin modes are identified. At the low-frequency end is the planetary wave basin mode, whose period is determined by the cross-basin time of the planetary wave on the poleward boundary of the basin...

Time-longitude diagrams of monthly anomalies of TOPEX/Poseidon sea surface height (SSH), Levitus steric height, COADS wind stress curl, as well as meridional surface wind averaged over the northern South China Sea (SCS) from 18° to 22°N, exhibit a coherent westward phase propagation, with a westward propagation speed of about 5 cm s−1. The consiste...

The Pacific decadal and interdecadal oscillation (PDO) has been extensively explored in recent decades because of its profound impact on global climate systems. It is a long-lived ENSO-like pattern of Pacific climate variability with a period of 10–30 years. The general picture is that the anomalously warm (cool) SSTs in the central North Pacific a...

A coupled ocean-atmosphere model study shows that the extratropical impact on tropical climate is as strong as the tropical impact on extratropical climate. A 2°C SST warming in the global extratropics increases equatorial ocean temperature by ~1°C in the surface and subsurface. The surface temperature change is caused by the atmospheric bridge of...

The temporal-spatial structure and the formation mechanisms of the South China Sea (SCS) circulation are studied using the Princeton Ocean Model (POM). The model well reproduces the observed sea surface height (SSH) annual cycle and some current system such as the SCS Western Boundary Current (SCSWBC) system and the Kuroshio Loop Current (KLC). Fou...

The South China Sea warm water (SCSWW) is identified as the warm water body with temperature no less than 28°C. There are three stages in the seasonal variation of the SCSWW. The SCSWW expands rapidly and deepens quickly in the developing stage. The warm water thickness decreases near the coast of Vietnam and increases near Palawan Island in the st...

The annual cycle characteristics of the SSH in the South China Sea (SCS) are analyzed based on the Sea Surface Height (SSH) anomaly data from the TOPEX / POSEIDON-ERS altimeter data and the Parallel Ocean Climate Model (POCM) prediction. The results show that the distributions of the SSH anomalies of the SCS in January, March and May, are opposite...

The evolution of decadal subduction temperature anomalies in the subtropical North Pacific is studied using a simple and a complex ocean model. It is found that the amplitude of the temperature anomaly decays faster than a passive tracer by about 30%-50%. The faster decay is caused by the divergence of group velocity of the subduction planetary wav...

Based on the Sverdrup relation, using climatological wind stress data, the basin scale Sverdrup transport in the South China Sea(SCS) is calculated and the basic seasonal features of the Sverdrup circulation are obtained. A comparison of these calculated features with observations proves that the wind-driven circulation in the SCS is very important...

Dynamics of the seasonal cycle of sea surface height (SSH) in the South China Sea (SCS) are studied using observations as well as numerical and theoretical models. Seasonal variability of the SCS is interpreted in light of large-scale dynamics and Rossby waves. It is found that the seasonal cycle over most of the SCS basin is determined predominant...

The dynamic characteristics of the seasonal thermocline in the deep sea region of the South China Sea were analyzed by using seasonal mean temperature climatology. The thermocline undergoes remarkably seasonal variation throughout a year, is thinnest and weakest in winter, and thickest in spring, strongest in summer and fall. Due to the upper Ekman...

The upper oceanic heat budget in the South China Sea (SCS) is studied on the basis of ocean surface heat flux, upper sea heat storage and horizontal oceanic heat transport calculated from Comprehensive Ocean and Atmosphere Data Set. Several useful conclusions can be obtained and they are helpful for us to understand the climatologically thermal con...