Supporting Information
The impact of equilibrating hemispheric albedos on tropical performance in
the HadGEM2-ES coupled climate model.
This supporting information gives additional specific information on analysis methods and results.
S1. Areas for Quantitative Analysis areas
The areas for quantitative analysis are based on those of Giorgi (2006) and are indicated in Figure
S1.
Supporting Information Figure S1. Showing the regions of investigation. CAM: Central America,
split into CAM-W and CAM-E; AMZ: Amazonia; AF: Sahelian Africa; SOF: Southern Africa,
SAS: South Asia; SEA: South East Asia. AF merges the original16 west Africa (WAF) and east
Africa regions (EAF), while CAM-E and CAM-W splits the CAM region at 97oW.
S2. Seasonal analysis for STRAT simulations
Figure S2 provides a qualitative assessment of the seasonal bias in HadGEM2-ES tropical
precipitation and the change in precipitation induced under the STRAT experiment.
Supporting Information Figure S2. a) The seasonal precipitation bias in HadGEM2-ES (mm
day-1) when compared against GPCP data (1979-1998). b) The seasonal change in precipitation
from equilibrating the hemispheric albedos in STRAT.
A quantitative analysis of the percentage changes in precipitation bias under the STRAT, OCEAN
and CLOUD experiments over the regions shown in Figure S1 are given in Table S1.
Season
DJF
MAM
JJA
SON
Region
AMZ
AF
SAS
CAM_W
CAM_E
SEA
SOF
AMZ
AF
SAS
CAM_W
CAM_E
SEA
SOF
AMZ
AF
SAS
CAM_W
CAM_E
SEA
SOF
AMZ
AF
SAS
CAM_W
CAM_E
SEA
SOF
HIST
GPCP
(mm day(mm day-1)
1)
5.88
7.16
0.46
0.30
0.58
0.67
0.69
1.43
1.83
2.03
6.41
8.03
5.07
5.83
5.79
6.54
2.31
1.81
1.73
1.35
0.66
1.36
2.06
2.22
5.75
6.82
3.06
2.67
3.08
4.35
4.65
3.91
7.41
6.79
3.50
4.60
5.66
4.49
5.54
5.26
0.51
0.54
3.77
5.13
2.83
2.42
3.52
2.45
2.14
3.71
4.84
4.02
6.32
5.54
2.10
3.16
Bias
reduction
STRAT %
59
44
-14
23
-27
10
-11
69
63
36
-18
-199
-5
-30
73
68
79
-27
99
-34
-21
86
85
35
20
73
4
13
Bias reduction
OCEAN %
Bias reduction
CLOUD %
58
85
-12
19
17
5
-42
77
93
73
-11
-314
-3
90
73
78
44
-61
83
26
97
74
64
63
12
81
56
11
34
43
-45
14
19
3
-14
32
42
40
-2
-287
-18
15
38
37
39
-48
59
-7
-23
49
43
24
-2
59
13
4
Supporting Information Table S1: The absolute values of the rainfall (mm day-1) in each of the
regions shown in Figure S1 from the GPCP data set and the HIST simulation. The improvement
(%) for simulations STRAT, OCEAN and CLOUD with respect to the HIST simulation is
calculated as 100 x (abs(HIST-GPCP) – abs(SIM-GPCP)) / abs(HIST-GPCP), where SIM is
either STRAT, OCEAN or CLOUD. Using this definition, positive values represent the percentage
improvement in precipitation (marked in red), and negative values represent the percentage
deterioration in precipitation (marked in black).
S3. Results from the atmosphere only simulations
Results from the HIST_FIXED_SST and STRAT_FIXED_SST simulations are compared to those
from HIST and STRAT in Figure S3.
Supporting Information Figure S3. Quantitative assessment of the change in the bias with respect
to GPCP for the JJA season over land in the following regions: AMZ: Amazonia, AF: Sahelian
Africa, SAS: South Asia, CAM-W: Central America West, CAM-E: Central America East, SEA:
South East Asia, SOF: Southern Africa (see Supporting Information Figure S1 for these regions)
for HIST, STRAT, HIST_FIXED_SST and STRAT_FIXED_SST simulations.
S4. The impact of equilibrating hemispheric albedos on the moisture flux and precipitation
Figure S4 shows the impact of equilibrating hemispheric albedos for the STRAT, OCEAN and
CLOUD experiments.
Supporting Information Figure S4. a) The change (STRAT-HIST) in precipitation (mm day-1) and the
moisture flux and moisture flux convergence/divergence at 925hPa (g kg-1ms-1) for 20year mean of JJA.
Colours represent changes in precipitation, vectors changes in moisture flux, and grey and black contours
changes in moisture flux convergence and divergence respectively. The moisture flux
divergence/convergence contour intervals are -6x10-8, -4x10-8, -2x10-8, 2x10-8, 4x10-8 and 6x10-8 in units of
kgkg-1s-1. b) and c) Show the same for OCEAN-HIST and CLOUD-HIST, respectively.
S5. The impact of equilibrating hemispheric albedos on the global meridional energy
transport.
The impact is shown in Figure S5.
HIST: OCEAN
HIST: ATMOS
STRAT: OCEAN
STRAT: ATMOS
Supporting Information Figure S5. The global northward energy transport (PW) by the atmosphere and
ocean from HIST and STRAT simulations.
S6. Demonstrating the improvement in hurricane frequency metrics
Supporting Information Figure S6. Analysis of the HIST and STRAT simulations, and comparison against
observed data (see Methods for details of observational data sets). MDR is the Maximum Development
Region defined by the area 10-20°N in the tropical Atlantic Ocean and the analysis is performed over the
June-November time period.
S7. The bias in SSTs in HIST and STRAT
a)
b)
Supporting Information Figure S7. Bias in annual mean SSTs (K) in the a) HIST and b) STRAT simulations
compared against SST climatologies derived from observations. The region shown is 45°N- 45°S.
S8. The SSTs gradients in HIST and STRAT compared against observations
Supporting Information Figure S8. The normalised tropical Atlantic June-August SSTs as a function of
latitude for the HIST and STRAT simulations compared with SSTs derived from observations (AMIP). The
normalisation procedure divides by the maximum SST in each case.
S9. Putting HadGEM2-ES in context with other models
Supporting Information Figure S9. Filled circles represent a) Hemispheric Temperature Asymmetry and b)
Atmospheric cross equatorial heat transport as a function of the precipitation asymmetry index defined by
HF13. A similar index (H15) defined as (Sahelian precipitation- Amazonian precipitation)/(Sahelian
precipitation + Amazonian precipitation) is shown by the diamonds in b) which is more representative of
the current analysis. The x and the + sign represent observational constraints on the HF13 index and H15
index respectively.