summer air-mass transformation: feedback among physical .../menu/standard... · 5 juli till 19...

Summer air-mass transformation: feedback among physical processes

in advection of warm air over melting sea ice

Michael Tjernström ([email protected])Department of Meteorology &

Bolin Centre for Climate Research Stockholm University, Sweden

Ian Brooks1, Joseph Sedlar2, Matt Shupe3, Ola Persson3, John Prytherch1, Dominic Salisbury1, Peggy Achtert1, Barbara Brooks1, and Georgia Sotiropoulou4

1Leeds University, Leeds, UK2Swedish Meteorological and Hydrological Institute, Norrköping, Sweden3NOAA/PSD & CIRES, Boulder, Colorado US4Stockholm University, Stockholm Sweden

2017-11-21 / Michael Tjernström, MISU

Arctic Clouds in Summer Experiment

(ACSE)

Part of the Swedish-Russian-US Arctic Ocean Investigation

of Climate-Crysophere-Carbon Interactions(SWERUS-C3)

Tromsö Barrow

5 juli till 19 augusti

Barrow Tromsö

21 augusti till 4 oktober

2017-11-2114th Conference on Polar Meteorology and Oceanography, Seattle

There and back again

Summer airmass transformationTransport in over sea ice

Tjernström et al. 2015

2017-11-21 Michael Tjernström, Stockholm University



Temperature (ºC)

Specific humidity (g kg-1)



Eq. Pot temp. (ºC)


FLW

FLW

FLW

FTurb



The hypothesis…

Surface inversions:

zi = z(T Tmax)

T0 <T(z < zi) <Tmax


Tjernström & Graversen 2009

SHEBA surface

inversions



Three cases:Ice cover >15% (51% of all)

• All cases with no surface

temperature inversions (62%)

• Surface temperature inversions with DQ

< 1 g kg-1 (“dry”; 13% or ~4 net days)

• Surface temperature inversions with DQ

> 1 g kg-1 (“moist”; 25% or ~8 net days)


Inversion statistics

Inversion statistics

2017-11-21 Michael Tjernström,Stockholm University

Meridional displacement

No inversion

Dry inversion

Moist inversion


From where does

the air come?

No surface inversion

Dry inversion

Moist inversion

Vertical displacement


From where does

the air come?


Integrated water


Lowest cloud base

Lowest

cloud top

Cloud

thickness


Surface energy budget

This much net solar radiation

(200 – 300 W m-2) could only

come from clear conditions.

Yet, the more cloudy “moist inversions”

have more net surface energy than the

less cloudy “dry inversions”

Is there a systematic sampling bias?


The solar radiation problem

Calculated incoming

clear-sky radiation

Almost

the same!

Observed shortwave

radiation divided by TOA

Observed shortwave radiation

divided by clear-sky


DoY 220 – 8 August

DoY 260 – 17 September


About -20 Wm-2

About 0 Wm-2

Using the transmissivity and

surface albedo time series, but

setting solar conditions constant

for all days, but taken from

different days

But what happens at the top of

the atmosphere?


Sedlar & Tjernström 2017

Using AIRS to find more episodes


Stability index

Moisture index


TOA OLR anomalies



2017-11-21 / Namn Namn, Institution eller liknande

AIRS 700 hPa anomalies

SEP

Take-home messages …

• Transport events lead to air-mass transformation

forcing feedbacks intimately coupled to the transport itself

• Moisture advection more important than heat advection?

• Hypothesis of an “extra-energy zone” for melting sea ice is

validated – sort of - but things are more complicated than

expected…

• Dry inversion contribute about – nothing in summer; loss of

clouds and therefore net longwave, radiation eats it all up…

• Moist inversions contribute about 10-20 W m-2 in summer

• Q: What is the atmospheric dynamics that determine the

inversion characteristics, and how can it be generalized? Is it

tied to the feedback on the feedback – on the height

anomalies?

2017-11-21 / Namn Namn, Institution eller liknande

Thanks for your attention

Surface inversions:

zi = z(T Tmax)

T(z < zi) > T0

HatPro temperature error


HatPro humidity error

Low-level jets…

summer air-mass transformation: feedback among physical .../menu/standard... · 5 juli till 19...

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