Transcript The Powerpoint file with my poster on the Antarctic Inversion

The Surface-based Temperature Inversion
on the Antarctic Plateau
Contact Information:
Stephen R. Hudson
University of Washington
Department of Atmospheric Sciences
Box 351640
Seattle WA 98195-1640; USA
Email: [email protected]
Stephen R. Hudson and Richard E. Brandt
University of Washington
1. Abstract
5. Effect of wind speed on 2- to 22-metre temperatures
The data from South Pole are used to:
 Present a climatology of inversion strength between 2 and 22 m above the surface
- An inversion is present over 50% of the time in summer and nearly 90% in winter.
 Examine the relationship between inversion strength in this layer and near-surface winds
- The strongest inversions often occur with winds of 3-5 m s-1, not with calm winds.
 Investigate the structure of the temperature profile in the lowest 2 m in winter
- The median temperature difference between 2 m and the surface is 1 K.
Data from Dome C allow us to examine the role of the diurnal cycle on the summertime
inversion. These data show that, while absent at the Pole, the diurnal cycle can be quite
significant over much of the Plateau; the average nighttime inversion during the summer at
Dome C is stronger than almost any inversion during the summer at South Pole.
Median and 10th and 90th percentiles of 2-metre air temperature as functions of wind speed
The temperature at 2 m is lowest and
the median inversion strength in the
2- to 22-metre layer is greatest with
winds of 3-5 m s-1, not with calm
winds.
-35
-40
-45
-50
T2 (°C)
Data from South Pole and Dome C Stations are used to characterize the surface-based
temperature inversion that is a dominant feature of the climate of the Antarctic Plateau.
There is some indication that the very
strongest inversions can occur with
calm winds, indicated by the double
maximum in the 90th percentile
inversion strength curve.
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-60
-65
-70
0
The data from South Pole include:
 Air temperatures at 2 and 22 m above the surface from 1994 through 2003 measured by
NOAA’s Climate Monitoring and Diagnostics Laboratory (CMDL)
 Wind speed at 10 m above the surface from 1994 through 2003 measured by CMDL
 Air temperatures at the surface and 20, 50, 100, and 200 cm above the surface for the
winter of 2001 measured during a University of Washington field project
The data from Dome C were collected during another University of Washington field project.
They cover the period 22 December 2004 to 31 January 2005 and include:
 Air temperatures at 2 and 30 m above the surface
 Snow-surface temperature measured by an infrared thermometer
3. Climatology of 2- to 22-metre inversion strength
Histograms of the temperature difference between 2 and 22 m show that the inversion is very
persistent; an inversion is present in this layer well over half of the time in summer and nearly
90% of the time in winter.
Wintertime inversions are much more variable, with a median strength of 1.7 K, but they
sometimes greatly exceed 10 K.
N = 697025
Mean = 0.4
Std = 0.7
Min = -1.2
Max = 7.5
40
30
25
20
15
Percentiles:
0.1% = -0.6
1% = -0.5
10% = -0.2
25% = -0.1
50% = 0.2
75% = 0.6
90% = 1.2
99% = 3.5
99.9% = 5.2
N = 2508884
Mean = 2.5
Std = 2.6
Min = -0.7
Max = 22.1
40
35
25
20
15
2
4
6
2
2
4
4
6
6
2
2
4
4
6
6
2
4
6
8
Temperature Difference (K)
0
10
0
8
10
Wind Speed (m s-1)
12
14
16
10
10
12
12
14
14
16
16
8
10
8
-1
Wind Speed (m s10
)
Wind Speed (m s-1)
12
12
14
14
16
16
7
-50
6
5
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4
Number
(thousands)
1
0
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-10
0
Using the 10 years of CMDL data, the top plot shows
the median (green) and the 10th and 90th percentiles
(blue and red) of temperature at 2 m at South Pole in
winter, as functions of wind speed. The middle plot
is the same, but for inversion strength between 2 and
22 m. The bottom plot shows the number of
observations in each 0.1 m s-1 wind-speed bin.
8
8
40
20
20
0
00
0
6. The diurnal cycle
Percentiles:
0.1% = -0.5
1% = -0.3
10% = 0.0
25% = 0.5
50% = 1.7
75% = 4.0
90% = 6.0
99% = 11.4
99.9% = 16.5
The average nighttime inversion strength between 2 and 30 m at Dome C in summer, 6 K, is
stronger than almost any inversion observed at South Pole in summer.
Half-hourly average temperature differences at Dome C in summer 2004/05
Half-hourly average temperatures at Dome C in summer 2004/05
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10
T30 - Tsfc
2
4
6
8
Temperature Difference (K)
10
8
30 m
5
0
16
2
-65
-28
0
14
9
10
5
12
10
20
-40
Inversion Strength (K)
10
30
10
-60
3
Temperature (°C)
Statistics of the temperature
difference between 2 and 22 m
at South Pole from 1994-2003.
The left panel shows data from
the two Antarctic-Plateau
summer months, and the right
from the six winter months.
Frequency (%)
35
45
8
Average daily temperature variations decrease from 13 K at the surface to about 3 K at 30 m, and
the times of maximum and minimum are further delayed as distance from the surface increases.
Winter (April through September)
Frequency (%)
45
6
The diurnal cycle is obviously absent at the South Pole, but these data, from Dome C, 15° north of
the Pole, show that the effect of the daily variation in solar elevation can be significant in other
parts of the Antarctic Plateau. During collection of these data the solar elevation angle ranged
from 3° to 38°, and it varied by 30° during each day.
In summer, temperature differences across this layer are generally less than 1 K, but stronger
inversions can form, occasionally exceeding a strength of 5 K.
Summer (December and January)
4
Median and 10th and
90th percentiles
of 2-metre air temperature as functions of wind speed
th
th
40
Median
and
10
and
90
percentiles
of inversion strength as functions of wind speed
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11
0
-45
80
(°C)
T22 -TT
2 2 (K)
The data presented here come from two Antarctic stations. Amundsen-Scott South Pole Station
is located at the Geographic South Pole, at an elevation of 2835 m; Dome C Station sits at 75° S,
123° E, at an elevation of 3200 m.
Number
Number
(thousands)
(thousands)
2. Data
The surprising location of the
temperature minimum and inversion
maximum may be explained by the
inversion wind, in which an inversion
over sloped terrain forces a wind
through thermal wind balance.
2
-30
-32
-34
2m
T30 - T2
6
4
T2 - Tsfc
2
-36
4. Temperature differences in the lowest 2 m
Surface
Distribution of T(2 m) - T(surface) in winter 2001 at South Pole
0
-38
35
(a) All Sky
30 N = 7752
Relative Frequency (%)
The inversion continues below 2 m, to the surface.
In winter, the median temperature difference between
2 m and the surface is 1 K, and about 1.3 K under clear
skies.
-40
0
2
4
6
8
25
10
12
14
Local Time (h)
16
18
20
22
24
-2
0
2
4
6
8
10
12
14
Local Time (h)
16
18
20
22
24
Half-hourly averages of temperatures at the surface and 2 and 20 m above the surface (left) and of the differences between the
three levels (right) at Dome C from 22 December 2004 to 31 January 2005.
20
15
10
5
0
Median temperature differences in lowest 2 m at South Pole in winter 2001
2.0
-1
0
1
2
T(2 m) - T(surface) (K)
3
4
1.8
Distribution of T(2 m) - T(surface) under clear skies in winter 2001 at South Pole
1.6
(b) Clear Sky
1.4
30 N = 3876
Relative Frequency (%)
Height (m)
Median temperature difference
relative to 2 m in winter (left).
Relative frequencies of
observed temperature
differences between 2 m and the
surface in winter (top right) and
under clear skies in winter
(bottom right). All 3 plots were
created with data from 21 March
to 21 September 2001.
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1.2
1.0
0.8
All Sky
0.6
0.4
0.2
0.0
-1.4
25
20
Acknowledgements
15
10
5
Clear Sky
-1.2
-1
-0.8
-0.6
-0.4
-0.2
Median Temperature Difference, T - T(2 m) (K)
0
0
-1
0
1
2
T(2 m) - T(surface) (K)
3
4
Thomas Mefford at CMDL provided the 10 years of South Pole data as well as assistance using them.
Michael Town, Thomas Grenfell, Delphine Six and Stephen Warren all helped collect the University
of Washington data. Stephen Warren also provided much guidance during the analysis.