ENSO and ENSO teleconnections
The El Niño Southern Oscillation (ENSO), is the leading driver of global-scale interannual climate variability. ENSO originates from the tropical Pacific and impacts global precipitation and temperature via atmospheric and oceanic teleconnections. However, it is still not clear whether the pattern and intensity of the teleconnections would change in response to external forcing internal climate variability. My research addresses this question using high-resolution proxy records, climate model simulations, and paleoclimate assimilation products.
(Du et al., 2021)
Interannual precipitation in Southern California:
We reported a new continuous, sub-annually resolved Southern California precipitation record for the Common Era and the Holocene, using scanning XRF data from marine sediments from the Santa Barbara Basin, and investigated its relationship with ENSO. The comparison between the high-resolution Southern California precipitation reconstruction and other atmospheric circulation records suggests both the Intertropical Convergence Zone (ITCZ) migration and mid-latitude atmospheric circulation strength modulate the ENSO teleconnection between the southwestern US and tropical Pacific. This work highlights that ENSO teleconnections could be nonstationary over the long term under different mean climate states.
Related Publications:
Du et al. (2020), Interannual Southern California precipitation variability during the Common Era and the ENSO teleconnection, Geophysical Research Letters.
Du et al. (2021), High-resolution interannual precipitation reconstruction of Southern California: Implications for Holocene ENSO evolution, Earth and Planetary Science Letters.
(Hakim et al., 2016)
ENSO and the Asian Summer Monsoon:
I am currently further investigating the dynamics of ENSO teleconnections, especially the relationship between the Asian summer monsoon and ENSO. The Asian summer monsoon supplies freshwater resources for nearly four billion people, but its predictability is still limited, partly due to its unstable relationship with ENSO. To tackle this issue, I am deciphering the influence of external forcing on the ENSO-Asian summer monsoon teleconnection, using CESM Last Millennium Ensemble outputs, paleoclimate data assimilation products, as well as new atmospheric model experiments.
Related Publications:
Du et al., Solar Irradiance Modulates the Asian Summer Monsoon - ENSO Relationship over the Last Millennium, Geophysical Research Letters. In Revision.
Tropical Hydroclimate Change Since the Last Ice Age
The Earth’s climate underwent large and well-known changes since the Last Glacial Maximum (~21,000 years ago), and therefore provides a unique opportunity to study tropical hydroclimate changes under different boundary conditions. However, the heterogeneity of proxy records and disagreement with model simulation results limits our understanding of regional hydrological response and the underlying large-scale climate dynamics. To address this challenge, I am using innovative modeling approaches which allow for more direct data-model comparison.
Indo-Pacific Warm Pool:
The Indo-Pacific Warm Pool is the largest source of atmospheric heating and moisture on Earth. I investigated hydroclimate and water isotope changes in this region by integrating the first set of isotope-enabled transient climate model simulations (iTRACE) and water isotope-based proxy records. This work demonstrated that changes in Maritime Continent land-sea configuration due to sea level rise exert a strong control on the long-term glacial to deglacial precipitation trend in the Indo-Pacific Warm Pool, with insolation forcing and greenhouse gas concentrations playing secondary roles. Moreover, we found the relationship between precipitation and its isotopic composition are location-dependent due to their heterogeneous response to different forcings across the Indo-Pacific Warm Pool.
Related Publication:
Du et al. (2022), Deglacial trends in Indo-Pacific warm pool hydroclimate in an isotope-enabled Earth system model and implications for isotope-based paleoclimate reconstructions. Quaternary Science Reviews.
(Du et al., 2022)
Tropical Indian Ocean:
A detailed data-model comparison over the tropical Indian Ocean reveals that the land-sea configuration in the Maritime Continent can also modulate the tropical Indian Ocean response to high-latitude meltwater flux on millennial timescales. Such modulation leads to changes in the zonal precipitation pattern over the tropical Indian Ocean, along with drought and extreme precipitation over East Africa and the Maritime Continent. This work highlights the impact of sea level change on the coupled ocean-atmosphere interaction over the tropical Indian Ocean. I am currently expanding this work to a pan-tropical scale to gain new insights into the large-scale dynamics of the tropical hydrological cycle since the last ice age.
Related Publication:
Du et al. (2023), A zonal dipole across the tropical Indian Ocean governed precipitation during Heinrich Stadial 1. Science Advances.
(Du et al., 2023)
Extreme Events and Ecosystem Response
Du et al., 2018
Flood history in Southern California:
We reported a new Southern California flood history record during the Holocene based on flood layers deposited in the Santa Barbara Basin. This long, continuous, and high-resolution record allows us to assess the magnitude and frequency of flood events in the past, and investigate the changes in flood events under different mean climate states. Additionally, I built up a new chronology for Holocene sediments in Santa Barbara Basin based on AMS 14C dates of planktonic foraminifera, and conducted accurate core-to-core stratigraphic correlation using flood and turbidite layers. This work provides an easily accessible chronology for forthcoming paleoclimate studies in the Santa Barbara Basin.
Related Publication:
Du et al. (2018), A 9000-year flood history for Southern California: A revised stratigraphy of varved sediments in Santa Barbara Basin. Marine Geology.
Vegetation Response to Hydroclimate Changes:
We are collaborating with Dr. Linda Heusser to compare a new high-resolution pollen record from the Santa Barbara Basin with regional precipitation records to investigate the vegetation response to hydroclimate changes, including megadroughts, extreme events, and wildfires.
Related Publication:
Du et al. Vegetation response to Southern California hydroclimate changes during the past 9000 years. (in prep)
