ENGLISH mastodon Mpimet wisskomm social Linkdn account Mpimet

Hongdou Fan

Abteilung Klimavariabilität
Gruppe Forschungsgruppe des Direktors (CVR)
Position Postdoc
Telefon +49 40 41173-153
Email hongdou.fan@mpimet.mpg.de
Raum B 213

 

I'm driven to understand different aspects about the Atlantic Meridional Overturning Circulation (AMOC). Specifically, my current research interests and activities include:

  • Understanding the downward limb of the AMOC: by understanding the stream function in depth coordinate and density coordinate and their connection, I try to reconcile the Eulerian perspective and Lagrangian perspective in terms of downward volume transport. 
  • Running storm- and eddy- resolving global coupled ICON simulations. This unprecedented simulation brings an extraordinary opportunity to better understand the entire chain of the AMOC.
  • Investigating the impact of greenhouse gas forcing on AMOC via its fingerprint of sea surface height. 

 

About me

 

I'm driven to understand different aspects about the Atlantic Meridional Overturning Circulation (AMOC). Specifically, my current research interests and activities include:

  • Understanding the downward limb of the AMOC: by understanding the stream function in depth coordinate and density coordinate and their connection, I try to reconcile the Eulerian perspective and Lagrangian perspective in terms of downward volume transport. 
  • Running storm- and eddy- resolving global coupled ICON simulations. This unprecedented simulation brings an extraordinary opportunity to better understand the entire chain of the AMOC.
  • Investigating the impact of greenhouse gas forcing on AMOC via its fingerprint of sea surface height. 

 

I am a member of the Steering Committee of EPOC – Explaining and Predicting the Ocean Conveyor Project. I serve as Work Package 4 (Future AMOC Evolution, Impacts and Abrupt Changes) and contribute to Work Package 2 (Key Processes of Meridional Transport). In addition, within Work Package 3, I investigate the impact of greenhouse gas forcing on the AMOC through its sea surface height fingerprint.

A Glance at My Research

The AMOC stream function and overturning transport
The AMOC stream function (Sv) in (a) density coordinates and remapped to (b) depth coordinates. The overturning transport in (c) density coordinates and remapped to (d) depth coordinates. In my current research, I reconcile the volume transport diagnosed in density space with that diagnosed in depth space.

Mixed layer depth (MLD) offers an intuitive view of how the upper ocean “breathes” with the seasons—and how mesoscale and submesoscale eddies continually reshape it. In winter, surface buoyancy loss triggers widespread convective mixing across the subpolar gyre, rapidly deepening the mixed layer. A particularly striking feature in the Irminger Basin is the appearance of near-circular patches of very deep MLD that coincide with anticyclonic mesoscale eddies, highlighting how eddies restratify the upper ocean. The realistic mixed layer depth structure substantially benefits from the eddy-rich km-scale resolution. My recent work shows that eddies contribute 24% of the regional transport—more than 1 Sv—from the Irminger Basin to the AMOC lower limb.

MPI-ESM
The regression of AMOC 26N onto sea surface height under different forcing experiments (control, greenhouse gas forcing fixed at 1950s levels, and historical forcings). Can we disentangle the impact of greenhouse gas forcing on AMOC via its fingerprint of sea surface height? Credit: Barcelona Martin, Jan

During my PhD, I found that the SPG provides downstream ocean predictability by modulating volume transport anomalies along the Atlantic water pathway. This dynamical link to the SPG causes salinity to be considerably better predicted than temperature in the Nordic Seas.
Time series of upper 310-m temperature in the Norwegian Sea
I further disentangled the role of the North Atlantic Oscillation (NAO) in the subdecadal variability of the Norwegian Sea upper-ocean temperature, and highlighted that the challenge in predicting Norwegian Sea temperature is inherent to the low predictability of the NAO due to chaotic dynamics.
During my Master study, I was intrigued by the predictability framework based on information theory. I extracted the most predictable patterns of the winter surface temperature in the Northern Hemisphere and developed a calibration scheme to improve the seasonal prediction skill. The calibration algorithm has been operational since 2021 and has contributed to the Chinese National Winter Forecast Annual Consultation.