1. Modeling of paleo-monsoon
Akio KITOH
Meteorological Research Institute, Japan Meteorological Agency
1: Use of paleo-climate modeling
2: 6ka (Mid-Holocene)
3: 21ka (Last Glacial Maximum)

2. Orogeny, plate motion and land-sea distribution
Uplift of the Himalayan/ Tibetan plateau and the retreat of the Paratethys played important role in driving the Asian monsoon changes
Ramstein et al. (1997) Nature

3. 4 types of large-scale forcing or b.c. for the South Asian monsoon
the monsoon is most sensitive to the elevation and radiation (orbital) changes
CCM1+50m mixed-layer
Kutzbach et al. (1993) J.Geology

4. Use of paleo climate modeling
Snapshot simulations of past climates by climate models can be very useful to investigate the physical mechanisms of climate change. They can be used for example to test the sensitivity of the climate system to supposed forcing of past climates such as variations in solar radiation, ice sheet extent or CO2.

5. Use of paleo climate modeling (cont)
Past climate simulations also allow us to test the simulated climate sensitivity. AGCM parameterizations are developed and validated by using present-day observations. However, current data cannot ensure that these parameterizations will produce a correct sensitivity of the climate. Past climates offer a unique opportunity to test model results in this respect, at least when sufficiently quantitative and globally distributed paleo-data are available and when the causes of the changes are deterministic and well quantified.

6. Last Glacial Maximum: 21ka

7. Dome Concordia (Antarctica): 740,000 years of climate change
(EPICA Members, 2004)

8. Mid-Holocene: 6ka
Tassili n’Ajjer, Algeria - Sahara was greener

15. Paleoclimate Modeling Intercomparison Project (PMIP)
PAGES/IGBP and WGNE/WCRP/CLIVAR
Mechanisms of climate change
sensitivity to model parameterizations
Evaluation of climat models
Model-model and model-Data comparisons
PMIP1 ( ):
AGCM AGCM-slab
Last Glacial Maximum, 21,000 yrs BP
Mid-Holocene, 6000 yrs BP
Early Holocene
Last glacial inception
Water hosing (CMIP/PMIP)
PMIP2 (2003-????):
OAGCM and OAVGCM

16. PMIP data: vegetation map

17. PMIP data: tropical water balance at LGM
plant-available moisture
runoff (equivalent to precipitation minus evaporation)

18. PMIP data: global lake status

19. PMIP data: diagnostic for mid-holocene precipitation over Northern Africa

20. Experiment Control run 6ka–run (mid-Holocene)
orbital parameters of 6,000 years ago
same CO2 concentration as in the control run
21ka–run (Last Glacial Maximum)
orbital parameters of 21,000 years ago
CO2 concentration 200 ppm
ice sheet (Peltier 1994)
control 6ka 21ka eccentricity
obliquity
precession

21. 6,000 yr BP monsoon
mid-Holocene

22. Insolation at present and 6,000 years ago
In the NH, insolation was larger in summer and less in winter. Annual mean insolation anomaly was positive in high latitudes, and was negative, about –1 W/m2, in the tropics.

23. TOA insolation difference at 6ka and 21ka
Note the different scale.
The 6ka has a larger seasonal variation with negative anomaly in NH winter and positive in NH summer.
In the tropics, annual mean difference is -1 W/m2 in 6ka and +1 W/m2 in 21ka.

24. Mid-Holocene climate
# The Afro-Asian summer monsoon was stronger and shifted northward
# Weaker and less frequent ENSO activity
# SSTs in the western Pacific were about 1oC warmer and rainfall was less variable
- more La Nina like state in the mean

25. 6ka JJA Surface Temp, Precip, Wind
MRI
6ka JJA Surface Temp, Precip, Wind
Afro-Asian monsoon shifts northward. Negative ground temp.
Easterly wind anom in the Western Pacific (stronger Walker). La Nina type.

26. 6ka DJF Surface Temp, Precip, Wind
MRI
6ka DJF Surface Temp, Precip, Wind
Strong Asian winter monsoon. Annual mean SST 0.35C decrease.

27. MRI
Sea Surface Salinity

28. MRI
Annual mean Hadley and Walker (30S-30N) circulation

29. PMIP
Following the insolation change, all PMIP models simulate an increased seasonal cycle of temperature over the continents of the northern hemisphere, reaching about +/-1C on global average for the winter/summer seasons.

30. PMIP
The summer warming reaches a maximum between 40N and 50N with more than 2C, whereas the cooling occurs further south, between 0N and 30N, with a similar magnitude.

31. 6ka GCM comparison

32. N Africa Precip
• Models do not reproduce precipitation to maintain steppe climate
• Importance of air-sea interaction and vegetation feedback

33. Jan-Feb-Mar Temperature difference (6ka–0ka) with 4 CGCMs
Zhao et al. 2004

34. Jul-Aug-Sep Temperature difference (6ka–0ka) with 4 CGCMs
Zhao et al. 2004

35. Jul-Aug-Sep Precipitation difference (6ka–0ka) with 4 CGCMs
Zhao et al. 2004

36. Jul-Aug-Sep 850hPa wind difference (6ka–0ka) with 4 CGCMs
Zhao et al. 2004

37. 6ka precipitation anomalies over northern Africa (20W-30E) by AGCM and CGCM
Maximum precip: N in AGCM 10-18N in CGCM

38. 21,000 yr BP monsoon
Last Glacial Maximum

40. Insolation at present and 21,000 years ago

41. PMIP
An annual mean global cooling of about 4C is obtained by all the models forced by the CLIMAP SST estimates. The range of cooling is larger when using computed SSTs, from –6C to –2C, since models are no longer constrained by the same change in SST.

42. PMIP
Compared to the fixed SST experiments, computed SST experiments produce a greater inter-hemispheric difference with a weaker cooling in the southern hemisphere due to less sea ice extent than prescribed by CLIMAP. In the tropics, computed SSTs are colder than CLIMAP, especially over the tropical Pacific where the warm pools of CLIMAP are not reproduced.

43. PMIP
According to both sets of PMIP simulations, the LGM climate is also more arid over most of the northern continents and in the tropics. At the regional scale, the simulations are characterized by a number of common features, including a reduction in the strength of the Afro-Asian monsoon and increased intertropical aridity.

44. 21ka JJA Surface Temp, Precip, Wind
MRI
21ka JJA Surface Temp, Precip, Wind
Weak monsoon. Dry and hot over India and Amazon.

45. 21ka DJF Surface Temp, Precip, Wind
MRI
21ka DJF Surface Temp, Precip, Wind
Weak trade winds. El Nino type response in the tropics.

46. 21ka annual mean SST: CLIMAP vs GCM
MRI
21ka annual mean SST: CLIMAP vs GCM
Large decrease in high latitudes.
East-west contrast in the tropics, larger decrease in the Caribbean.
Positive SST anomaly in the subtropical Pacific.

47. Temperature profile near Hawaii
MRI
Temperature profile near Hawaii
• Steeper lapse rate at LGM
• positive temperature anomaly only near surface

48. LGM Precip: Observed proxy vs GCM top pollen data
MRI
LGM Precip: Observed proxy vs GCM
top pollen data
middle lake level data
bottom GCM (P - E)
Farrera et al Clim Dyn

50. SST, sd(SST), T20C depth and zonal wind stress at the equator
MRI

51. Sea temperature and its zonal gradient along the equator
Mean response: La Nina type in 6ka, El Nino type in 21ka.
Zonal temperature gradient: small in 6ka, large in 21ka.
MRI

52. Summary of paleo simulations
6ka ka
SST ℃ ℃
Precipitation % %
Afro-Asian Summer monsoon strong weak
Afro-Asian Monsoon rainbelt north south
East Asian Winter monsoon strong strong
Pacific trades strong weak
Tropical climate La Nina type El Nino type
Tropical SST variability weak strong

53. ・ How does the climate model project as a future climate?
・ Can we use the past warm-day climate as a proxy of the future climate?

54. JJA Precipitation & 850hPa Winds
MRI
JJA Precipitation & 850hPa Winds
Northward shift of monsoon westerly and intensified rainfall over the Afro-Asian summer monsoon region.
Easterly anomaly over the western tropical Pacific associated with strengthened subtropical anticyclones.

55. JJA Precipitation: CO2 vs 6ka
MRI
JJA Precipitation: CO2 vs 6ka
Overall resemblance.
In the 6ka run, a northward shift of the Afro-Asian monsoon rainfall belt is more pronounced with a decrease over the ocean south of India.

56. JJA 850hPa Winds: CO2 vs 6ka MRI Also similar each other.
There is a northward shift of monsoon westerly around India, easterly anomaly in the western Pacific, westerly anomaly around Japan, and westerly anomaly in the equatorial eastern Pacific.

57. JJA Surface Temperature: CO2 vs 6ka
MRI
JJA Surface Temperature: CO2 vs 6ka
The CO2 run shows an overall increase with its maximum in the 40 deg latitude. There is a mimimum over the monsoon rain belt due to increased rainfall.
In the 6ka run, temperature increases in the northern continent. The monsoon rain belt corresponds to negative temperature anomaly. SST lower about 0.4 deg C.

58. SST standard deviation
MRI
SST standard deviation
In both runs, the SST variability in the tropical Pacific decreased. At least for the 6ka run, the model result is consistent with the coral record.

59. MRI
850hPa Winds
The trade wind is stronger and the easterly anomaly prevails over the central and western equatorial Pacific, resulting in changes in mean ocean thermal structure.

60. Ocean Temperature at Equator
MRI
Ocean Temperature at Equator 0m
300m
A warm water piles up in the western Pacific, resulting in a decrease in zonal temperature gradient in the central equatorial Pacific.

61. Paleo-ENSO

62. A long term record of Oxygen-18 isotope data from corals in the western Indian Ocean off Kenya compared against the COADS SST record for recent years.
From CLIVAR web-site

63. Coral records show weaker and less frequent ENSO activity in mid-Holocene. SSTs in the western tropical Pacific was about 1 deg warmer and rainfall was less variable, suggesting a more La Nina like mean state.

64. ENSO Reconstruction

65. Control run: global SST EOF1 and regressions

66. 6ka run: global SST EOF1 and regressions

67. Power spectrum of NINO3.4 SST and SST EOF1

68. Regression on NINO3.4 SST
0ka
6ka

70. Future issues ocean vegetation dust ice sheet …