PDF, 684KB

On the factors controlling the
surface temperature
and 2-m 2 m air temperature
over the Arctic sea ice in winter
Roberta Pirazzini 1,2 and Timo Vihma 1
1
Finnish Institute of Marine Research
2
University of Helsinki, Finland
Photo: NASA

Which factors control the surface temperature (T S ) and
2-m m air temperature (T 2m ) over sea ice in winter?
1. Lateral advection of heat from lower latitudes;
2. turbulent exchange with the surface and the inversion layer capping the ABL;
3. radiative fluxes.
T S
and T 2m
are are strongly coupled through the sensible heat flux
but
T S
is more directly affected by radiative fluxes than T 2m
.
T 2m
is directly affected by lateral heat advection.
Objective of this study:
To study the relative importance of the factors responsible for the observed
synoptic-scale temperature variations over the Arctic sea ice in winter

• Winter
cyclon tracks
• Adapted from
Serreze and Barry,
1988.
Photo: Bruce Ramsay

Data
→ From the Russian Ice Stations:
NP-27 (winter 1986-1987)
NP-28 (winters 1986-1987 and 1987-1988)
NP-29 (winter 1987-1988)
NP-30 (winters 1987-1988 and 1989-1990)
we utilised synoptic data (3 hour intervals):
– surface temperature (T S
),
– 2-m air temperature (T 2m
),
– cloud cover (total and low clouds),
– wind speed
– wind direction
– surface pressure
→ From ECMWF re-analyses, ERA-15 (resolution of 1.125° x 1.125°,
pressure levels from 1000 to 600 hPa)
– We calculated the lateral heat advection at the site of each Ice Station once per
day (at 00 UTC).

Methods applied
• We classify the data into various cases, following Walsh and Chapman
(1998):
cloudy skies (N > 7/10) and clear skies (N < 4)
strong winds (so that 33% of cases exceed a high speed threshold)
and weak wind (so that 33% of cases were below a low speed threshold)
• In addition, we study the heat advection. To focus on the direct effect of it,
we analyse the heat advection at 1000 hPa level.
warm advection (so that 33% of cases exceed a warm threshold)
and cold advection (so that 33% of cases were below a cold threshold)
• To simplify the analyses, we study the potential temperature instead of the
temperature
• We study in more detail some single episodes of warm advection.

Monthly mean surface potential temperature θ s (thick lines)
and 2-m 2 m air potential temperature θ 2m (thin lines)
• Strong coupling between surface
and 2-m air potential temperature.
3h change → controlled by cloud
cover and advection
24h change → controlled by
advection
Magnitude → controlled by cloud
cover and wind speed

Monthly mean surface - air
potential temperature difference
θ s - θ 2m
• Cloud fraction is the most important factor.
• In March, θ s
- θ 2m
increases and neither the effects of cloud cover, advection
nor wind speed make much difference.

Monthly mean (a) 2-m 2 m air potential temperature and (b) surface - air
potential temperature difference for:
- warm advection (red) - cold advection (blue)
- cloudy skies (solid lines) - clear skies (dashed lines)
- strong winds (thick lines)
- weak winds (thin lines)
• θ 2m : - clear skies + weak winds →θ 2m ~ - 40ºC
- clear skies + strong winds →θ 2m increases ~ 5ºC
- cloudy skies + weak winds →θ 2m increases ~ 5-9ºC
- cloudy skies + strong winds →θ 2m increases ~ 10-20ºC
- to reach the warmest temperatures, also warm advection
is required
• θ s - θ 2m : - cloud fraction is more important than wind speed

6.0
5.0
Temperature advection ( o C/3h)
4.0
3.0
2.0
1.0
0.0
-1.0
-2.0
-3.0
01/01/87
31/12/86
6.0
Temperature advection ( o C/3hours)
5.0
4.0
3.0
2.0
1.0
0.0
-1.0
-2.0
-3.0
01/01/87
31/12/86
Case studies: warm advection episodes in December 1986
Case studies: warm advection episodes in December 1986
(a) 3 to 4 December (b) 6 to 9 December
(c) 11to 16 December (d) 23 to 26 December
0
NP-27
a) b)
-5
-10
-15
-20
-25
-30
-35
-40
-45
-50
-55
-60
0
-5
-10
-15
-20
-25
-30
-35
-40
-45
NP-28
-50
-55
-60
01/12/86
02/12/86
03/12/86
04/12/86
05/12/86
06/12/86
07/12/86
08/12/86
09/12/86
10/12/86
11/12/86
12/12/86
13/12/86
14/12/86
15/12/86
16/12/86
17/12/86
18/12/86
19/12/86
20/12/86
21/12/86
22/12/86
23/12/86
24/12/86
25/12/86
26/12/86
27/12/86
28/12/86
29/12/86
30/12/86
Air temperature ( o C)
01/12/86
02/12/86
03/12/86
04/12/86
05/12/86
06/12/86
07/12/86
08/12/86
09/12/86
10/12/86
11/12/86
12/12/86
13/12/86
14/12/86
15/12/86
16/12/86
17/12/86
18/12/86
19/12/86
20/12/86
21/12/86
22/12/86
23/12/86
24/12/86
25/12/86
26/12/86
27/12/86
28/12/86
29/12/86
30/12/86
Air temperature ( o C)
NP-27
NP-28
NP-27
NP-28
a)
Ta (oC)
Advection > 0
Advection < 0
Tair (oC)
Advection > 0
Advection < 0
c)
NP-27
NP-28
d)
NP-27
b)
NP-28
Slp from ECMWF re-analysis (ERA-15)

Acknowledgments
• Russian scientists who collected the data
• ECMWF
• Finnish Cultural Foundation
Photo: NASA