Geography
257 Topics
in Climatology Fall
2009
This
semesterÕs topic: The interhemispheric
gradient in tropical climate and climate change
Instructor: Prof.
John Chiang
Time: Tuesdays
2p-4p, 55A McCone. NOTE: First meeting will be Tue 9/1 at **2PM**.
Synopsis: The goal for this
semester is to explore how useful the concept of the Ôinterhemispheric
gradientÕ is in characterizing tropical climate and climate change. Interhemispheric thermal gradients come
up in many different contexts, but is probably most well known in Tropical
Atlantic Variability (TAV) where interannual-decadal variations in sea surface
temperature (SST) is characterized by Ôdipole-likeÕ behavior. However, they also appear in many other
contexts e.g.: SST patterns associated with Sahel rainfall variations, and the
Òmeridional modeÕ variation in the tropical Pacific. In paleoclimate they are most prominent in climate impacts
of thermohaline shutdown scenarios.
And of course, they are also implicated in control of the seasonal cycle
of the Intertropical Convergence Zone.
In this seminar, we will review various
climate variability and change scenarios where the interhemispheric gradient is
prominent, and in the process ask two basic questions i) where do the
interhemispheric gradients come from; and ii) why do the tropics respond to it,
and how does it respond? An
interesting avenue to explore with the former question on forcing is whether or
not interhemispheric gradients are relevant in future climate change, in
particular given the large hemispheric differences in aerosol forcings, and
also the hemispheric asymmetric nature of warming due to anthropogenic
greenhouse gases.
Website (schedule updated weekly): http://www.atmos.berkeley.edu/~jchiang/Geog257/geog257.html
Prerequisites: Atmospheric
physics and dynamics at least at the level of the upper division
'Atmospheric Physics and Dynamics' course (GeogC139 / EPS181); or permission
from instructor.
Class
Schedule (red is preliminary and subject to change)
|
Week
and date |
Topic |
Reading |
|
1
(9/1) |
Logistics |
|
|
2
(9/8) |
Tropical
surface winds and SST |
[Lindzen and Nigam, 1987]; also skim [Chiang et al., 2001] |
|
3
(9/15) |
No
class – JC away |
|
|
4
(9/22) |
Tropical
Atlantic variability |
[Xie and Carton 2004]; also skim [Chiang and Vimont, 2004] |
|
5
(9/29) |
Seasonal
cycle of ITCZ/cold tongue – seasonal cycle |
[Chang, 1994]; also skim [Chiang et al., 2008] |
|
6
(10/6) |
ITCZ/cold
tongue – mean state |
[Xie and Philander, 1994] |
|
7
(10/12) **NOTE change of day |
Why
is the ITCZ north of the equator? |
[Philander et al., 1996]; also skim [Takahashi and Battisti, 2007] |
|
8
(10/20) |
Subtropical
Anticyclones and Summer Monsoons |
Rodwell and Hoskins 2001 |
|
9
(10/27) |
NH
cooling and ITCZ |
[Broccoli et al., 2006; Chiang and Bitz, 2005]; also skim [Broccoli et al. 2006] |
|
10
(11/3) |
Onset
of the cold tongue |
[Philander and Fedorov, 2003] |
|
11(11/10) |
Interhemispheric
gradients and the tropical climate - dynamics |
[Kang et al., 2009] |
|
12(11/17) |
Climate
response to AMOC shutdown |
[Cheng et al., 2007] |
|
13(11/24) |
Groups
meeting talk – Rei Ueyama (U Washington) |
|
|
14
(12/1) |
Atlantic
Multidecadal Oscillation |
Kerr (2005); and [Knight et al., 2005; Knight et al., 2006] |
|
15
(12/8) |
Aerosols
and tropical rainfall |
[Rotstayn and Lohmann, 2002] |
Broccoli, A. J.,
et al. (2006), Response of the ITCZ to Northern Hemisphere cooling, Geophysical
Research Letters, 33(1).
Chang, P. (1994), A Study of the Seasonal Cycle of
Sea-Surface Temperature in the Tropical Pacific-Ocean Using Reduced Gravity
Models, Journal of Geophysical Research-Oceans, 99(C4), 7725-7741.
Cheng, W., et al. (2007), Adjustment of the global climate
to an abrupt slowdown of the Atlantic meridional overturning circulation, in Past
and Future Changes of the OceanÕs Meridional Overturning Circulation:
Mechanisms and Impacts, edited by A.
Schmittner, et al., American Geophysical Union.
Chiang, J. C. H., et al. (2001), Relative roles of elevated
heating and surface temperature gradients in driving anomalous surface winds
over tropical oceans, Journal of the Atmospheric Sciences, 58(11),
1371-1394.
Chiang, J. C. H., and D. J. Vimont (2004), Analogous Pacific
and Atlantic meridional modes of tropical atmosphere-ocean variability, Journal
of Climate, 17(21), 4143-4158.
Chiang, J. C. H., and C. M. Bitz (2005), Influence of high
latitude ice cover on the marine Intertropical Convergence Zone, Climate
Dynamics, 25(5), 477-496.
Chiang, J. C. H., et al. (2008), Interhemispheric thermal
gradient and tropical Pacific climate, Geophysical Research Letters, 35.
Kang, S. M., et al. (2009), The Tropical Response to
Extratropical Thermal Forcing in an Idealized GCM: The Importance of Radiative
Feedbacks and Convective Parameterization, Journal of the Atmospheric
Sciences, 66(9), 2812-2827.
Knight, J. R., et al. (2005), A signature of persistent
natural thermohaline circulation cycles in observed climate, Geophysical
Research Letters, 32(20).
Knight, J. R., et al. (2006), Climate impacts of the
Atlantic Multidecadal Oscillation, Geophysical Research Letters, 33(17).
Lindzen, R. S., and S. Nigam (1987), On the role of
sea-surface temperature gradients in forcing low-level winds and convergence in
the tropics, Journal of the Atmospheric Sciences, 44, 2440-2458.
Philander, S. G., and A. V. Fedorov (2003), Role of tropics
in changing the response to Milankovich forcing some three million years ago, Paleoceanography, 18(2),
-.
Philander, S. G. H., et al. (1996), Why the ITCZ is mostly
north of the equator, Journal of Climate,
9(12), 2958-2972.
Rotstayn, L. D., and U. Lohmann (2002), Tropical rainfall
trends and the indirect aerosol effect, Journal of Climate, 15(15),
2103-2116.
Takahashi, K., and D. S. Battisti (2007), Processes
controlling the mean tropical pacific precipitation pattern. Part I: The Andes
and the eastern Pacific ITCZ, Journal of Climate, 20(14), 3434-3451.
Xie, S. P., and S. G. H. Philander (1994), A Coupled
Ocean-Atmosphere Model of Relevance to the Itcz in the Eastern Pacific, Tellus
Series a-Dynamic Meteorology and Oceanography,
46(4), 340-350.
Xie, SP and J. Carton (1994), Tropical Atlantic Variability: Patterns, Mechanisms, and Impacts. In EarthÕs Climate: The Ocean-Atmosphere Interaction eds. Wang, Xie, and Carton. pp 121-142