Date: September 28, 2023
Location: OCNPS 200

The Ocean & Earth Sciences departmental seminar informs students, staff, faculty, and the University community about recent issues. Please join us for a reception in OCNPS 404 after the seminar.

Speaker: Richard Sullivan, ODU                                                                

Host: Wallace

Zoom: Contact Susan Craig for Link


Seasonal hydroclimate in the Intra-American Seas (IAS) is mediated by a confluence of interactive climate modes, including the intertropical convergence zone, the El Nino southern oscillation (ENSO), and the North Atlantic Subtropical High (NASH).

The NASH, a semi-permanent anti-cyclone in the sub-tropical Atlantic, expands westward along steep land-sea temperature gradients during the boreal summer and suppresses convection, increases divergence, and influences the trajectory of Atlantic hurricanes. Additionally, the maximum extent of the NASH is responsible for a recurrent mid-summer drought in the IAS, while meridional displacements of the NASH western edge create a dipole that drives rainfall/aridity in the eastern IAS and southeast United States. Therefore, understanding the full range of NASH dynamics is critical to ensuring the water-security of low-lying coastal communities and vulnerable small island states in the IAS, many of which are already at risk due to rising sea levels and projected decreases in annual precipitation. However, little is known about how the NASH impacts regional precipitation and storminess on timelines commensurate with future climate change scenarios.

To address this deficiency, we employ a combination of paleo-proxy reconstructions and numerical simulations of regional hydroclimate to examine the influence of the NASH at centennial scales. Through the analysis of a ~6,000 year-long reconstruction of paleo-rainfall derived from sediment cores recovered from the Bahamas, reconstructions of Common Era tropical cyclone activity from the Yucatan peninsula, numerical simulations from the Community Earth System Model-Last Millennium Ensemble, and 1150 years of statistically downscaled synthetic Atlantic tropical cyclones, we identify recurrent patterns of hydroclimate volatility related to NASH positioning not observed in the modern era. These include:

  1. Multi-centennial intervals of increased (decreased) aridity in the north (south) IAS related to meridional displacements of the NASH and
  2. Prolonged intervals of suppressed (enhanced) tropical cyclone susceptibility along the eastern US (west Caribbean) coastlines concurrent with NASH westward expansion.

This analysis highlights previously unexplored patterns in north Atlantic climate and provides critical insight into the ocean-atmosphere processes that modulate rainfall and storminess across regions already threatened by hydroclimate instability.