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7/29/2019 AGU 2012 Poster Final
http://slidepdf.com/reader/full/agu-2012-poster-final 1/1
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Objectives
Methods
Results
Conclusions and Implications
Future Work
Introduction
To investigate the climatic effects of lowered sea level by altering the land mask inan Atmospheric General Circulation Model (AGCM) to reflect exposed LGM land.
Effects of interest include: 1) changes in mean tropical Indo-Pacific climate and b)
changes in the tropical and extratropical responses to the El Nino-Southern
Oscillation.
• Utilized the atmospheric general circulation mod el SPEEDY8
- Simplified Parametrizations, primitivE-Equation Dynamics
- 3.75Lon x 3.70Lat resolution, 8 Vertical Levels
• In control run, SSTs were prescribed from 10S to 10N, with a 50m slab ocean
elsewhere.
• In LGM run, the landmask was altered to approximate expanded LGM
landmasses from N. Australia to N. China (Figure 2). The new land gridpoints
were assigned on a sliding scale of 0.1 to 1, according to the percentage of land
vs. ocean in the specific gridcell.• Both runs were forced by 1950-2010 prescribed SSTs in the 10S-10N tropical
domain; 50 ensembles were run for the control and the LGM configuration.
• A combination of statistical methods were employed to investigate the
climate signals of interest; the significance of any changes observed between the
control and LGM simulations were assessed with a Monte Carlo approach.
Mean Precipitation
• significantly wetter conditions over new land cover areas, with drier
conditions in immediate surrounding area
• off the Sunda Shelf, opposing bands of wet/dry anomalies saddle the
equator from the western Indian to the central Pacific, suggesting a shift in
the location or intensity of the Intertropical Convergence Zone
Considering the significant response of theatmospheric circulation patterns to the presence of
the Sunda Shelf in SPEEDY, it is i mportant to
investigate how the response varies in a coupled O-
A model such as the NCAR CESM. The suite of
atmospheric signals presented here may either be
damped for amplified by O-A coupling.
References
Figure 2 ) The modern (left) and LGM (middle) masks. The right panel il lustrates
the % ocean assignments for each of the coastal red gridpoints in the middle panel,
where 0.1 = 10% ocean and 0.9% = 90% ocean).
(1) Tudhope, AW; Chilcott, CP; McCulloch, MT; et. al. Science 291 (2001): 1511-1517.
(2) Lea, DW; Pak, DK; Spero, HJ. Science 289 (2000): 1719-1724.(3) Koutavas, A; Lynch-Stieglitz, J; Marchitto, TM; et al. Science
297 (2002): 226-230.(4) Martinez, JI; DeDeckker, P; Chivas, AR. Marine
Micropaleontology 32 (1997): 311-340.
(5) Partin, J.P., Cobb, K.M., et al., Nature (2007): 452 -455. (6) Bush, ABG; Fairbanks, RG. Journal of Geophysical Research
108 (2003): 1-10.(7) DiNezio, PM; Clement, A; Vecchi, GA; et al.Paleoceanography 26 (2011): 1-26.
(8) Molteni, F. Climate Dynamics 20 (2003): 175-191.
Modern LGM LGM - Modern
Figure 2) The modern-day Bering Strait (left) was closed during the LGM (right)
The largest change in LGM land/ocean configuration, apart from the Sunda
Shelf, is the closure of the Bering Strait. This may have effects on the ocean’s
thermohaline circulation, and/or impact North Pacific ocean-atmosphere climate
variability. If so, then this would have consequences for the buildup or maintenance
of large continental ice sheets in North American and Eurasia. Future work will focus
on simulating the climate effects of a closed Bering Strait.
1. Mean state
2. Response to El Nino-Southern Oscillation SST forcing
Precipitation
• around the Sunda Shelf, rainfall in the northern Warm Pool region
decreased, and increased in the southern Warm Pool regions
•pattern of response different than changes in mean precipitation; butabout half as large as changes in mean precipitation
Figure 1) Comparison of modern-day Indo-Pacific (left) to LGM (right).http://www.ngdc.noaa.gov/mgg/topo/globega2.html
The effect of lowered sea level on Indo-Pacific climate as simulated by the SPEEDY AGCMEleanor A. Middlemas, Kim M. Cobb, Emanuele Di Lorenzo
Georgia Institute of Technology [email protected]
Climate during the Last Glacial Maximum is characterized by lower
atmospheric CO2, increased albedo, large continental ice sheets, and altered
ocean circulation. The effect of a 125m fall sea level is typically considered
negligible, despite the presence of a newly-exposed continental-sized landmass
in the Indo-Pacific, referred to as the ‘Sunda Shelf’.
Paleoclimate records indicatethat during the LGM, El-Nino
Southern Oscillation was weaker1,
the sea-surface temperature
gradient along the equatorial pacific
may have changed2,3, and that the
western Pacific may have been drier
than today4,5.
The only modeling experiment that attempted to isolate the effects of
the Sunda Shelf on LGM climate documented significant changes in the
tropical Pacific atmospheric circulation6. A recent survey of coupled O-A
climate models found that the Sunda Shelf drove a weakening of Warm Pool
convection that varied in strength among the different models7.
Results and Discussion
This undergraduate research
was supported by NSF.
The presenter would appreciate
discussing graduate research
opportunities available in your lab.
3. Teleconnected responses in the North Pacific
Mean Precipitation
Precipitation (mm/day) Precipitation (mm/day) Precipitation anomalies (mm/day)
mm/day
Mean Vertical Velocity (ω)
Precipitation Regressed on NINO34
EOF1 of Sea Level Pressure
SST regressed on PC1 of Sea Level Pressure
(Pa/s) (Pa/s) (Pa/s)
80-N
40-N
60-N
20-N
0
20-N
60-S
40-N
80-S
80-N
40-N
60-N
20-N
0
20-N
60-S
40-N
80-S
80-N
40-N
60-N
20-N
0
20-N
60-S
40-N
80-S
80-N
40-N
60-N
20-N
0
20-N
60-S
40-N
80-S
80-N
40-N
60-N
20-N
0
20-N
60-S
40-N
80-S
80-N
40-N
60-N
20-N
0
20-N
60-S
40-N
80-S
80-N
40-N
60-N
20-N
0
20-N
60-S
40-N
80-S
60-N
50-N
40-N
30-N
20-N
10-N
60-N
50-N
40-N
30-N
20-N
10-N
60-N
50-N
40-N
30-N
20-N
10-N
60-N
50-N
40-N
30-N
20-N
10-N
60-N
50-N
40-N
30-N20-N
10-N
60-N
50-N
40-N
30-N20-N
10-N
50-N
40-N
30-N
20-N
10-N
0
10-S
20-S
40-N
30-N
20-N
10-N
0
10-S
20-S
30-S
40-S
-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 -0.1 -0.06 -0.02 0 0.02 0.06 0.1
-0.25 - 0.15 -0.05 0 0.25 0.15 0.25-1 -0.5 0 0.5 1-1 -0.5 0 0.5 1
0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2
-0.06 -0.04 -0.02 0 0.02 0.04 0.06 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 -0.025 -0.015 -0.005 0 0.005 0.015 0.025
-5 -4 -3 -2 -1 0 1 2 3 4 5 -5 -4 -3 -2 -1 0 1 2 3 4 5 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
Mean Vertical Velocity
• changes mirror precipitation changes, with increased vertical advection
associated with increased rainfall in the new land cover areas
Sea Level Pressure
• Aleutian low variability increased by approximately 15%, likely
associated with a stronger extratropical response to ENSO variability
• Extratropical SST response to associated atmospheric anomalies
consistent with stronger basin-scale response to tropical ENSO variability
Exposing the Sunda Shelf surrounding areas has significant impacts on Indo-Pacific mean climate
state climate, with the largest responses located in the Sunda Shelf region itself. Significant
atmospheric changes extend into the western Indian Ocean and into the Northern Pacific.
Comparisons with proxies from these regions awaits a similar experiment performed with a fully-
coupled climate model, but it is clear that the presence of the Sunda Shelf likely altered precipitation
in the near vicinity of the landmass, as discussed in previous work, and possibly in ENSO-sensitive
regions. It is critically important to distinguish the sea level response in Indo-Pacific proxies from
the response associated with lower CO2/cooler global temperatures, in order to better constrain
how this region may respond to rising temperatures in the coming decades.
hPa hPa hPa
Temperature (°C) Temperature (°C) Temperature (°C)
mm/day mm/day mm/day
