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  • 1
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    Amplified seasonal cycle in hydroclimate over the Amazon river basin and its plume region (2020)
    Nature Research
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Liang, Y., Lo, M., Lan, C., Seo, H., Ummenhofer, C. C., Yeager, S., Wu, R., & Steffen, J. D. Amplified seasonal cycle in hydroclimate over the Amazon river basin and its plume region. Nature Communications, 11(1), (2020): 4390, doi:10.1038/s41467-020-18187-0.
    Description: The Amazon river basin receives ~2000 mm of precipitation annually and contributes ~17% of global river freshwater input to the oceans; its hydroclimatic variations can exert profound impacts on the marine ecosystem in the Amazon plume region (APR) and have potential far-reaching influences on hydroclimate over the tropical Atlantic. Here, we show that an amplified seasonal cycle of Amazonia precipitation, represented by the annual difference between maximum and minimum values, during the period 1979–2018, leads to enhanced seasonalities in both Amazon river discharge and APR ocean salinity. An atmospheric moisture budget analysis shows that these enhanced seasonal cycles are associated with similar amplifications in the atmospheric vertical and horizontal moisture advections. Hierarchical sensitivity experiments using global climate models quantify the relationships of these enhanced seasonalities. The results suggest that an intensified hydroclimatological cycle may develop in the Amazonia atmosphere-land-ocean coupled system, favouring more extreme terrestrial and marine conditions.
    Description: M.-H.L., C.-W.L., and R.-J.W. are supported by the Ministry of Science and Technology in Taiwan under grant 106-2111-M-002-010-MY4. H.S. and J.D.S. are grateful for support from NOAA NA19OAR4310376 and NA17OAR4310255. C.C.U. acknowledges support from the U.S. National Science Foundation under grant OCE-1663704. The National Center for Atmospheric Research (NCAR) is a major facility sponsored by the US National Science Foundation (NSF) under Cooperative Agreement No. 1852977. We thank Dr. Young-Oh Kwon at Woods Hole Oceanographic Institution and Dr. Who Kim at NCAR for discussions about the ocean model experiment design. We thank Dr. Mehnaz Rashid at National Taiwan University and Wen-Yin Wu at the University of Texas at Austin in helping generate the high-resolution Amazon river mask. We also thank Dr. Gael Forget at Massachusetts Institue of Technology for comments on using ECCO and other ocean-state estimate products.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    Substantial sea surface temperature cooling in the Banda Sea associated with the Madden-Julian Oscillation in the boreal winter of 2015 (2021)
    American Geophysical Union
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    Publication Date: 2022-05-27
    Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(6), (2021): e2021JC017226, https://doi.org/10.1029/2021JC017226.
    Description: Substantial (∼2°C) basin averaged sea surface temperature (SST) cooling in the Banda Sea occurred in less than a 14-day period during the 2015 boreal winter Madden-Julian Oscillation (MJO). Such rapid and large cooling associated with the MJO has not been reported at least in the last two decades. Processes that control the substantial cooling during the 2015 MJO event are examined using high-resolution ocean reanalysis and one-dimensional (1-D) ocean model simulations. Previous studies suggest that MJO-induced SST variability in the Banda Sea is primarily controlled by surface heat flux. However, heat budget analysis of the model indicates that entrainment cooling produced by vertical mixing contributes more than surface heat flux for driving the basin-wide SST cooling during the 2015 event. Analysis of the ocean reanalysis further demonstrates that the prominent coastal upwelling around islands in the southern basin occurs near the end of the cooling period. The upwelled cold waters are advected by MJO-induced surface currents to a large area within the Banda Sea, which further maintains the basin-wide cold SST. These results are compared with another MJO-driven substantial cooling event during the boreal winter of 2007 in which the cooling is mostly driven by surface heat flux. Sensitivity experiments, in which initial temperature conditions for the two events are replaced by each other, demonstrate that the elevated thermocline associated with the 2015 strong El Niño is largely responsible for the intensified cooling generated by the vertical mixing with colder subsurface waters.
    Description: This research is supported by NOAA grant NA17OAR4310256. TS and SP are supported by DOD grant W911NF-20-1-0309. TS is also supported by NSF grant OCE-1658218 and NASA grant NNX17AH25G. HS and JS acknowledge the support from NOAA under NA17OAR4310255. HS is also grateful for additional support from ONR (N00014-17-1-2398).
    Description: 2021-11-30
    Keywords: Banda Sea ; sea surface temperature ; Madden-Julian Oscillation (MJO) ; mixed layer processes ; El Niño-Southern Oscillation (ENSO) ; Maritime Continent
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    Upper-ocean response to precipitation forcing in an ocean model hindcast of Hurricane Gonzalo (2021)
    American Meteorological Society
    Details
    Publication Date: 2022-05-27
    Description: Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 50(11),(2020): 3219–3234, https://doi.org/10.1175/JPO-D-19-0277.1.
    Description: Preexisting, oceanic barrier layers have been shown to limit turbulent mixing and suppress mixed layer cooling during the forced stage of a tropical cyclone (TC). Furthermore, an understanding of barrier layer evolution during TC passage is mostly unexplored. High precipitation rates within TCs provide a large freshwater flux to the surface that alters upper-ocean stratification and can act as a potential mechanism to strengthen the barrier layer. Ocean glider observations from the Bermuda Institute of Ocean Sciences (BIOS) indicate that a strong barrier layer developed during the approach and passage of Hurricane Gonzalo (2014), primarily as a result of freshening within the upper 30 m of the ocean. Therefore, an ocean model case study of Hurricane Gonzalo has been designed to investigate how precipitation affects upper-ocean stratification and sea surface temperature (SST) cooling during TC passage. Ocean model hindcasts of Hurricane Gonzalo characterize the upper-ocean response to TC precipitation forcing. Three different vertical mixing parameterizations are tested to determine their sensitivity to precipitation forcing. For all turbulent mixing schemes, TC precipitation produces near-surface freshening of about 0.3 psu, which is consistent with previous studies and in situ ocean observations. The influence of precipitation-induced changes to the SST response is more complicated, but generally modifies SSTs by ±0.3°C. Precipitation forcing creates a dynamical coupling between upper-ocean stratification and current shear that is largely responsible for the heterogeneous response in modeled SSTs.
    Description: This work was supported by the National Aeronautics and Space Administration (NASA; Grant NNX15AD45G) and the National Oceanic and Atmospheric Administration (NOAA; Grant NA11OAR4320199).
    Keywords: Air-sea interaction ; Hurricanes/typhoons ; Salinity ; Ocean models
    Repository Name: Woods Hole Open Access Server
    Type: Article
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