Coastal upwelling regions

1
Coastal upwelling regions

• John Donners
• UK-Japan Climate Collaboration / HiGEM
• NCAS Climate
• University of Reading

2
Introduction

• Coastal upwelling regions are a strongly coupled
  system of clouds, winds and SST.
• Important for fisheries, carbon cycle and coastal
  communities.
• Observations suggest intensification in the last
  century.
• Modelling studies used either regional, uncoupled
  models or coarse, global models.
• The SSTs in HiGEM vs. HadGEM decrease in these
  regions, improving the simulation.

3
Changes in summer SSTsat increased atmosphere
res.
4
Changes in summer sw. rad. at increased
atmosphere res.
5
More low clouds at increased atmosphere resolution
6
RH_at_1000mbar increases in the NH
HadGEM
HiAtmos
7
Mechanism unclear in SH
RH_at_925mbar HiGEM-HadGEM
Liquid cloud water_at_925mbar HiGEM-HadGEM
8
Seasonal cycle of SST
9
Upwelling
summer
winter
10
Ocean temperature
11
Deep upwelling
Warning different color scales!
25mm/s gt 65 m/month
5mm/s gt 13 m/month
Observations tens to hundreds m/month
12
Cloud feedback to upwelled SST
13
Future upwelling?

• Transient climate change simulation 2 CO2
  incr./year
• Averaged over 20 years, 2x CO2
• Suggests that upwelling regions intensify and
  warm up less than their surroundings.

14
Summary

• Global coupled models lacked resolution to
  represent upwelling adequately regional studies
  used atmosphere- or ocean-only models.
• Both higher atmosphere and ocean resolution
  improve the seasonal cycle of SSTs either due to
  cloud or upwelling effects.
• Upwelling at higher ocean resolution is
  concentrated near the coastline, drawing colder
  water from deeper down the water column.
• Cloud feedback enhances SST cooling due to
  upwelling.

15
The end
16
Unsolved mysteries
17
Seasonal cycle of SSTs in SH

• No decrease in the amplitude of the seasonal
  cycle.
• Cloud feedback to cold, upwelled SSTs only
  important in the NH?
• Influence of Agulhas rings?
• Orographic forcing of the Andes mountain range?

18
SST variability
SST variability decreases with resolution in the
NH in closer agreement with obs. However, the SH
shows again a different behaviour, with hardly
any change in SST variability. Suggests stronger
coupling of cloud and SST in the NH than in the
SH?