Weiqing Han

• University of Colorado Boulder

Atlantic Niño can influence ENSO by modulating the Pacific Walker circulation. This interbasin connection is dominated by central Atlantic Niño (CAN) events, which began to emerge around 2000. Our analysis of observational data and climate model simulations reveals that the influence of CAN on ENSO will strengthen in a warming climate due to an enh...

The drivers of low-frequency (i.e., interannual to multidecadal) variability and change in the ocean heat content (OHC) on the U.S. North East shelf (USNES) are investigated through heat budget analysis and Regional Ocean Modeling System experiments. Surface heat flux on the USNES has been responsible for warming since 1977, and it dominates the in...

Extreme Indian Ocean dipole events (EXIODs) exert pronounced climate impacts both regionally and globally, which are closely associated with their sea surface temperature anomalies (SSTAs). Here we find an evident asymmetry in SSTA patterns between the positive (EXpIOD) and negative (EXnIOD) phases of the EXIOD. Specifically, the warm SSTA center o...

The spatiotemporal characteristics of the south Sri Lanka coastal current (SSLCC) during summer are examined in this study. Climatologically, the SSLCC flows eastward as a part of the southwest monsoon current during summer. However, westward SSLCC occurred lasting more than 20 days in the summer of 2013, 2016, 2017, and 2018 based on reanalysis da...

It is well known that the intra‐seasonal component is critical for the occurrence of the westward south Sri Lanka coastal current (SSLCC) during summer. In this study, the relative contributions and physical processes that determine the westward SSLCC during summer on the intra‐seasonal timescale are quantified using the reanalysis data and a simpl...

A critical issue is determining the factors that control the year-to-year variability in precipitation over Southern Asia. In this study, we employ a cyclo-stationary linear inverse model (CS-LIM) to quantify the relative contribution of tropical Pacific and Indian Ocean sea surface temperature anomalies (SSTA) to the interannual variability of the...

The tropical Indian Ocean has experienced pronounced warming trends in recent decades, with dynamical processes recognized as key drivers. However, the role of thermodynamic processes remains uncertain due to discrepancies in surface wind-induced heat flux across existing datasets. Here, we utilize a machine learning algorithm to integrate in-situ...

The impact of interbasin linkage on the weather/climate and ecosystems is significantly broader and profounder than that of only appearing in an individual basin. Here, we reveal that a decadal linkage of sea surface temperature (SST) has emerged between western Australian coast and western–central tropical Pacific since 1985, associated with conti...

Plain Language Summary The subseasonal variability of Indian Summer Monsoon (ISM) is vital to agriculture and economy. Therefore, it is important to understand the drivers of ISM subseasonal anomalies, how strong an impact of a driver is, as well as potential changes in the strength of such an impact. In this study, we explore the possible drivers...

Coastal flooding induced by sea surface High EXtreme (HEX) events is an increasing risk to human society and infrastructure as both urban growth in coastal areas and anthropogenic sea level rise continue, especially for island nations like Indonesia. This paper investigates the role of atmospheric IntraSeasonal Oscillations (ISOs), which are domina...

The Madden–Julian Oscillation (MJO) is a dominant source of subseasonal atmospheric variability in the tropics and significantly impacts global weather and climate predictability. Changes in its activity and predictability due to human-induced global climate change have profound implications for future global weather prediction. Here we investigate...

The Atlantic Niño is characterized by sea surface warming in the equatorial Atlantic, which can trigger La Niña, the cold phase of El Niño-Southern Oscillation (ENSO). Although observations show that the Atlantic Niño has weakened by approximately 30% since the 1970s, its remote influence on ENSO remains strong. Here, we show that this apparent dis...

The contributions of local and remote forcings to the interannual sea level anomalies (SLAs) along the U.S. east coast (USEC) during the satellite altimetry era from 1993-2019 are quantified with analytical models assisted by statistical method. The local forcings from alongshore wind stress, sea level pressure via inverted barometer (IB) effect, a...

Plain Language Summary Alongshore wind stress and sea level pressure (SLP) are important regional forces in driving low‐frequency (interannual‐to‐decadal) sea level anomalies along the U.S. east coast. The roles of these regional forcings, however, vary with time, season, and region, which can shift the location and change the frequency and intensi...

Modes of climate variability can affect weather extremes, posing intractable challenges to our environment. However, to what extent climate modes can modulate heatwaves in China under a warming background remains poorly understood. Here, we examine the changes in heatwave intensity in seven distinct regions: three East, two middle, and two west reg...

A previous study demonstrated that atmospheric rivers (ARs) generate substantial air-sea fluxes in the northeast Pacific. Since the southeast Indian Ocean is one of the active regions of ARs, similar air-sea fluxes could be produced. However, the spatial pattern of sea surface temperature (SST) in the southeast Indian Ocean, especially along the we...

The Atlantic meridional overturning circulation is an important global-scale oceanic circulation, and its changes may be responsible for past abrupt climate change events. By using two versions of a coupled climate model, here we show that the stability of this circulation depends not only on the background climate, but also on the type of primary...

Low‐frequency (Interannual and longer timescale) variability in sea surface temperature (SST) of the Indian Ocean plays a crucial role in affecting the regional climate. Using a high‐resolution global model simulation, we show that internal oceanic variability is an important cause of the observed low‐frequency variability in the subtropical‐midlat...

Plain Language Summary The tropical Southeast Indian Ocean (SEIO) connects the three oceans and contributes to the global mass and heat exchanges. The changing freshwater storage and heat content in the SEIO impact regional and global climates. Positive Indian Ocean Dipole (pIOD) is a pattern of internal variability with anomalously low sea surface...

Abstract Despite the well‐recognized initial value nature of the subseasonal forecasts, the role of subsurface ocean initialization in subseasonal forecasts remains underexplored. Using observing system experiments, this study investigates the impact of ocean in situ data assimilation on the propagation of Madden–Julian Oscillation (MJO) events acr...

Previous theoretical studies suggest that the topography along the west coast of Australia plays an important role in strengthening and trapping the Leeuwin Current (LC) at the coast. To isolate and quantify the effect of the continental shelf and slope on the LC and Ningaloo Niño, high-resolution (1/12°) ocean general circulation model experiments...

The South Equatorial Current (SEC) in the south Indian Ocean (SIO) contributes to mass and heat exchanges among the Pacific, Indian, and Atlantic Oceans. By analyzing satellite and in situ observations, this study examines the seasonal structure and the interannual variability of the SEC. The SEC is mainly part of the Seychelles‐Chagos thermocline...

Low-lying island nations like Indonesia are vulnerable to sea level Height EXtremes (HEXs). When compounded by marine heatwaves, HEXs have larger ecological and societal impact. Here we combine observations with model simulations, to investigate the HEXs and Compound Height-Heat Extremes (CHHEXs) along the Indian Ocean coast of Indonesia in recent...

This study uses two reanalysis datasets and ocean model experiments to examine the dynamics of the interannual variability of the equatorial currents in the Indian Ocean, and to quantify the effects of the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) climate modes on the currents. Strong interannual variability of the equat...

Using mooring observations and reanalysis, we show that anomalously strong westward Equatorial Undercurrent (wEUC) developed in June–July in 2016 and 1998 in the Indian Ocean, which coincided with extreme Indian Ocean Dipole (IOD) and El Niño events. Simulations show that equatorial Kelvin and Rossby waves were excited by winds associated with El N...

A narrow eastward jet is detected beneath the westward‐flowing South Equatorial Current in the tropical South Indian Ocean (SIO) using in‐situ observation and reanalysis data. This jet is dubbed the South Equatorial Undercurrent (SEUC). The SEUC exists across the basin from about 60° to 105°E, with a core centered around 8°S in the west and shifted...

The subtropical Indian Ocean Dipole (SIOD) and Ningaloo Niño are the two dominant modes of interannual climate variability in the subtropical South Indian Ocean. Observations show that the SIOD has been weakening in the recent decades, while Ningaloo Niño has been strengthening. In this study, we investigate the causes for such changes by analyzing...

Atlantic Niño is the Atlantic equivalent of El Niño-Southern Oscillation (ENSO), and it has prominent impacts on regional and global climate. Existing studies suggest that the Atlantic Niño may arise from local atmosphere-ocean interaction and is sometimes triggered by the Atlantic Meridional Mode (AMM), with overall weak ENSO contribution. By anal...

The subtropical oceans between 35°-20°S in the Southern Hemisphere (SH) have exhibited prevailingly rapid sea-level rise (SLR) rates since the mid-20 th century, amplifying damages of coastal hazards and exerting increasing threats to South America, Africa, and Australia. Yet, mechanisms of the observed SLR have not been firmly established, and its...

Understanding the impact of the Indian Ocean Dipole (IOD) on El Niño-Southern Oscillation (ENSO) is important for climate prediction. By analyzing observational data and performing Indian and Pacific Ocean pacemaker experiments using a state-of-the-art climate model, we find that a positive IOD (pIOD) can favor both cold and warm sea surface temper...

An unprecedented extreme positive Indian Ocean Dipole event (pIOD) occurred in 2019, which has caused widespread disastrous impacts on countries bordering the Indian Ocean, including the East African floods and vast bushfires in Australia. Here we investigate the causes for the 2019 pIOD by analyzing multiple observational datasets and performing n...

Initialized Earth System predictions are made by starting a numerical prediction model in a state as consistent as possible to observations and running it forward in time for up to 10 years. Skilful predictions at time slices from subseasonal to seasonal (S2S), seasonal to interannual (S2I) and seasonal to decadal (S2D) offer information useful for...

The low-lying coastal and island regions are vulnerable to sea level rise and extreme events. Compounded by marine heatwaves, sea level extremes have devastating impacts on coastal community and marine ecosystems. As long tide gauge records are sparse, sea level extremes around Indonesia are poorly understood, and the Compound Height-Heat EXtreme (...

Ningaloo Niño (Niña) is associated with positive (negative) sea surface temperature anomalies off the west coast of Australia and is known to develop in austral summer. This chapter reviews past studies on this phenomenon, with a focus on its generation mechanisms, relations with other modes of interannual and decadal climate variability in the Ind...

The Indian Ocean has received increasing attention for its large impacts on regional and global climate. However, sea surface temperature (SST) variability arising from Indian Ocean internal processes has not been well understood particularly on decadal and longer timescales, and the external influence from the Tropical Pacific has not been quantif...

The Indian Ocean Observing System (IndOOS), established in 2006, is a multinational network of sustained oceanic measurements that underpin understanding and forecasting of weather and climate for the Indian Ocean region and beyond. Almost one-third of humanity lives around the Indian Ocean, many in countries dependent on fisheries and rain-fed agr...

The Madden-Julian Oscillation (MJO) is the dominant intraseasonal variability of the tropical troposphere. Many MJOs originate from the tropical Indian Ocean and propagate into the Pacific via the Maritime Continent (MC). However, 30%–50% of the MJO stalls over the MC, while its cause remains unclear. Here, we find that a new interbasin coupled phe...

Despite having some of the world's most densely populated and vulnerable coastlines, Indian Ocean sea level variability over the past century is poorly understood relative to other ocean basins primarily, due to the short and sparse observational records. In an attempt to overcome the limitations imposed by the lack of adequate observations, we hav...

Using 4-year mooring observations and ocean circulation model experiments, this study characterizes the spatial and temporal variability of the Equatorial Intermediate Current (EIC; 200~1200m) in the Indian Ocean and investigates the causes. The EIC is dominated by seasonal and intraseasonal variability, with interannual variability being weak. The...

1 The first baroclinic mode Rossby wave is known to be of critical importance to the 2 annual sea level variability in the southern tropical Indian Ocean (STIO; 0°S~20°S, 3 50°E~115°E). In this study, an analysis of continuously stratified linear ocean model 4 reveals that the second baroclinic mode also has significant contribution to the annual 5...

Seasonal prediction of western North Pacific summer monsoon rainfall (WNPSMR) is in great demand but remains challenging, because the relationships between the Asian monsoon system and precursors are nonstationary and exhibit significant decadal changes. The present study aims to (1) examine decadal variations of the relationships between the WNPSM...

In the eastern tropical Indian Ocean, intraseasonal variability (ISV) affects the regional oceanography and marine ecosystems. Mooring and satellite observations documented two periods of unusually weak ISV during the past two decades, associated with suppressed baroclinic instability of the South Equatorial Current. Regression analysis and model s...

The first baroclinic mode Rossby wave is known to be of critical importance to the annual sea level variability in the southern tropical Indian Ocean (STIO; 0°S~20°S, 50°E~115°E). In this study, an analysis of continuously stratified linear ocean model reveals that the second baroclinic mode also has significant contribution to the annual sea level...

Multi-time-scale variabilities of the Indian Ocean (IO) temperature over 0–700 m are revisited from the perspective of vertical structure. Analysis of historical data for 1955–2018 identifies two dominant types of vertical structures that account for respectively 70.5% and 21.2% of the total variance on interannual-to-interdecadal time scales with...

Previous work has demonstrated the strong ocean response to atmospheric rivers (ARs) in the northeast Pacific including coastal currents along the west coast of North America, because of strong surface winds associated with ARs. A recent study on the global distribution of ARs also suggests that the southeast Indian Ocean is one of the areas of rel...

Observational analyses and ocean general circulation model experiments were performed to understand the influence of oceanic processes on warm sea surface temperature anomalies (SSTAs) prior to convection initiation of boreal winter intraseasonal oscillations (ISOs), including the Madden‐Julian Oscillation (MJO), in the tropical Indian Ocean. We fo...

This poster is based on our recently published work at Journal of Climate. (Zhang&Han_2019) and was presented at the Ocean Science Meeting 2020 in San Diego.

The 78th edition of CLIVAR Exchanges focuses on the recent decadal review of the Indian Ocean Observing System (IndOOS) and its outcomes.

Plain Language Summary Salinity modulates the upper ocean circulation and temperature by changing the density of seawater and dynamical/themodynamical processes that control them. Recent studies have demonstrated that the tropical Indian Ocean experiences significant salinity variation associated with the Indian Ocean Dipole (IOD), which is a domin...

Full Report of IndOOS-2. The Indian Ocean Observing System (IndOOS) is a network of all the sustained observations in the Indian Ocean. Here we present IndOOS-2, designed for the future, to address changing societal and scientific priorities.

Mechanisms of salinity anomalies associated with the positive Indian Ocean Dipole (pIOD) are investigated through a series of sensitivity experiments and an online budget analysis using a regional ocean model. Special emphasis is placed on the contribution from the rectified effects due to high‐frequency variability, which was not quantitatively di...

This paper investigates interannual variability of the tropical Indian Ocean (IO) upwelling through analyzing satellite and in situ observations from 1993-2016 using the conventional Static Linear regression Model (SLM) and Bayesian Dynamical Linear Model (DLM), and performing experiments using a linear ocean model. The analysis also extends back t...

Projections of future sterodynamic sea level change from global climate models are associated with different sources of uncertainty. From a scientific, societal and policy-making perspective, it is relevant to both understand and reduce uncertainty in projections of climate change. Here, we review recent findings which describe, and shed light on,...

Global sea level rise (SLR) associated with a warming climate exerts significant stress on coastal societies and low-lying island regions. The rates of coastal SLR observed in the past few decades, however, have large spatial and temporal differences from the global mean, which to a large part have been attributed to basin-scale climate modes. In t...

A greater warming trend of sea surface temperature (SST) in the tropical Indian Ocean than in the tropical Pacific is a robust feature found in various observational datasets. Yet, this interbasin warming contrast is not present in climate models. Here we investigate the impact of tropical Indian Ocean warming on the tropical Pacific response to an...

Monitoring and Predicting Regional to Coastal Sea Level: Towards Comprehensive Observing and Modeling Systems

The Indian Ocean Observing System (IndOOS) is an observing network of profiling floats (Argo), a moored tropical array (RAMA), repeat lines of temperature profiles (XBT network), surface drifters (GDP), and tide gauges. Augmenting these networks are satellite remotely-sensed observations, in particular of surface winds, sea level, sea surface tempe...

Four-year (2014–17) zonal current data observed by a mooring at (5°N, 90.5°E) in the eastern Indian Ocean show a strong semiannual cycle in the middepth (~1200 m) with distinct vertical structure. This pronounced middepth semiannual variability, however, is inconsistent with the local wind forcing, which shows a predominant annual cycle. The underl...

In this study, the Indian Ocean upper-ocean variability associated with the Subtropical Indian Ocean Dipole (SIOD) is investigated. We find that the SIOD is associated with a prominent southwest-northeast sea level anomaly (SLA) dipole over the western-central South Indian Ocean, with the north pole located in the Seychelles-Chagos thermocline ridg...

A major challenge for managing impacts and implementing effective mitigation measures and adaptation strategies for coastal zones affected by future sea level (SL) rise is our limited capacity to predict SL change at the coast on relevant spatial and temporal scales. Predicting coastal SL requires the ability to monitor and simulate a multitude of...

The southeast Indian Ocean (SEIO) exhibits decadal variability in sea surface temperature (SST) with amplitudes of ∼0.2-0.3 K and covaries with the central Pacific (r = -0.63 with Niño-4 index for 1975-2010). In this study, the generation mechanisms of decadal SST variability are explored using an ocean general circulation model (OGCM), and its imp...

The Indian Ocean is warming faster than any of the global oceans and its climate is uniquely driven by the presence of a landmass at low latitudes, which causes monsoonal winds and reversing currents. The food, water, and energy security in the Indian Ocean rim countries and islands are intrinsically tied to its climate, with marine environmental g...

The rectification of intraseasonal wind forcing on interannual sea surface temperature anomalies (SSTA) and sea level anomalies (SLA) associated with El Niño–Southern Oscillation (ENSO) during 1993–2016 are investigated using the LICOM ocean general circulation model forced with daily winds. The comparisons of the experiments with and without the i...

This study investigates the impact of salinity stratification on the upper-ocean response to a category 5 tropical cyclone, Phailin, that crossed the northern Bay of Bengal (BOB) from 8 to 13 October 2013. A drastic increase of up to 5.0 psu in sea surface salinity (SSS) was observed after Phailin’s passage, whereas a weak drop of below 0.5°C was o...

By analyzing in situ observations and conducting a series of ocean general circulation model experiments, this study investigates the physical processes controlling intraseasonal variability (ISV) of the Equatorial Undercurrent (EUC) of the Indian Ocean. ISV of EUC leads to time-varying water exchanges between the western and eastern equatorial Ind...

Generation and development mechanisms of the Ningaloo Niño are investigated using ocean and atmospheric general circulation model experiments. Consistent with previous studies, northerly wind anomalies off the West Australian coast are critical in generating warm sea surface temperature (SST) anomalies of the Ningaloo Niño, which induce SST warming...

Air-sea coupling processes over the North Indian Ocean associated with the Indian summer monsoon intraseasonal oscillation (MISO) are investigated. Observations show that MISO convection anomalies affect underlying sea surface temperature (SST) through changes in surface shortwave radiation and surface latent heat flux. In turn, SST anomalies may a...

Ocean heat uptake is the primary heat sink of the globe and modulates its surface warming rate. In situ observations during the past half century documented obvious multidecadal variations in the upper-ocean heat content (0-400 m; OHC400) of the Indian Ocean (IO). The observed OHC400 showed an increase of (5.9 ± 2.5) × 10²¹ J decade⁻¹ during 1965-7...

The Ningaloo Niño refers to the evident interannual variability of sea surface temperature anomalies (SSTA) in the southeast Indian Ocean (SEIO), which can be caused by the Pacific La Niña. Through performing atmospheric general circulation model (AGCM) experiments, this study shows that the Ningaloo Niño can also actively impact on the tropical Pa...

Previous studies suggest that anthropogenic warming has affected the multi-decadal trend patterns of sea level over the Indian Ocean (IO). This effect, however, has not been quantified. Using observational datasets combined with large ensemble experiments from two climate models, this paper assesses the effects of natural internal variability versu...

This paper investigates the features of the Equatorial Intermediate Current (EIC) in the Indian Ocean and its relationship with basin resonance at the semiannual time scale by using in–situ observations, reanalysis output, and a continuously stratified linear ocean model (LOM). The observational results show that the EIC is characterized by promine...

Observational analyses and a hierarchy of ocean general circulation model (OGCM) experiments were performed to understand the influence of oceanic processes on the warm sea surface temperature anomalies (SSTAs) prior to the convection initiation of Indian summer monsoon intraseasonal oscillations (MISOs) in the equatorial Indian Ocean. Satellite ob...

Observational analyses and a hierarchy of ocean general circulation model (OGCM) experiments were performed to understand the influence of oceanic processes on the warm sea surface temperature anomalies (SSTAs) prior to the convection initiation of Indian summer monsoon intraseasonal oscillations (MISOs) in the equatorial Indian Ocean. Satellite ob...

Northward-propagating Indian summer monsoon intraseasonal oscillations (MISOs) are a major origin of the active-break spells of the monsoon rainfall. Forecast results for 28 active and 27 break spells from the National Centers for Environmental Prediction (NCEP) Climate Forecast System, version 2 (CFSv2), during 1999-2010 are analyzed. CFSv2 foreca...

Recent studies have linked interannual sea level variability and extreme events along the U.S. northeast coast (NEC) to the North Atlantic Oscillation (NAO), a natural internal climate mode that prevails in the North Atlantic Ocean. The correlation between the NAO index and coastal sea level north of Cape Hatteras was weak from the 1960s to the mid...

Observations show that decadal (10-20yrs) to inter-decadal (>20yrs) variability of tropical Indian Ocean (TIO) sea surface temperature (SST) closely follows that of the Pacific until the 1960s. Since then, the TIO SST exhibits a persistent warming trend, whereas the Pacific SST shows large-amplitude fluctuations associated with the Inter-decadal Pa...

Using satellite and in-situ observations, ocean reanalysis products and model simulations, we show a distinct reversal of the North Indian Ocean (NIO, north of 5°S) sea level decadal trend between 1993–2003 and 2004–3013, after the global mean sea level rise is removed. Sea level falls from 1993 to 2003 (Period I) but rises sharply from 2004 to 201...

The rapid Indian Ocean warming during the early-21th century was a major heat sink for the recent global surface warming slowdown. Analysis of observational data and ocean model experiments reveals that during 2003-2012 more than half of the increased upper Indian Ocean heat content was concentrated in the southeast Indian Ocean (SEIO), causing a w...

During the CINDY/DYNAMO field campaign, exceptionally large upper ocean responses to strong westerly wind events associated with the Madden–Julian oscillation (MJO) were observed in the central equatorial Indian Ocean. Strong eastward equatorial currents in the upper ocean lasted more than one month from late November 2011 to early January 2012. Th...