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Role of tropical Pacific SSTs in global medieval hydro climate

tropical Pacific SSTs Role of hydro-climate in global medieval: A modeling study (PDF format, 2.1 MB) is an interesting study of Burgman et al. from the year 2010.

handles your work, the following question:

The current research seeks to test the influence of persistent La Nina-like tropical Pacific SSTs [sea surface temperature, W.v.B.] alone in forcing medieval hydroclimate using a state of the art climate model. A detailed examination of the North American hydroclimatic response is discussed by Seager et al. [2008][1], and here we focus on the global response. A high‐resolution paleo‐proxy coral‐based SST record from the central Pacific is used to reconstruct tropical Pacific SSTs for the period 1320–1462 A.D. The resulting SST reconstruction is used to force an ensemble of climate model simulations. Modeled estimates of medieval hydroclimate are compared to simulations forced by observed SSTs and the differences are verified using paleo‐proxy records of medieval hydroclimate from around the world.

Für uns von Interesse are of course the long-term proxy data. Burgman et al. given here 30 different proxies, from different continents. I knew most of the proxies, including new for me were the work of Gupta et al. on the Arabian peninsula " (21) (PDF format, 376 KB) from the year 2003 and Bar-Mathews et al's. Labor in the Soreq Cave, Israel (29), from the year 1998 [2]. Recent work on the Soreq cave to be Bar-Mathews homepage mentioned.

In Figure 1a, the results of the modeling are given:

Figure 1 (A) Long term mean differences of vertically integrated soil wetness (shaded, (mm3H2O)/(mm3soil)) and SST (contour, 0.10 C) between POGA‐1L [model simulation, W.v.B.] (1320–1462 A.D.) and GOGA simulation (1856–2005 A.D.) overlaid with records of medieval hydroclimate and SST. SST records are plotted as red (warm) or blue (cool) dots relative to modern observations. Green and brown dots indicate proxy records of wet or dry medieval hydroclimate. The numbers cross reference the records to the references in the text and Table S1 (see auxiliary material). The medieval period is taken to be, approximately, from 800 A.D. to 1500 (adapted from Seager et al. [2007]). (b) The long term mean difference in Precipitation minus Evaporation (P‐E is shaded, units are mm/month, significance levels of 95% stippled) and 200mb geopotential height (contours, units are meters) for the winter half year between the POGA‐1L simulation (1320–1462 A.D.) and the modern GOGA simulation (1886–1998A.D.). The difference in the zonal average P‐E is offset to the right.

Erklärend erfahren wir:

Figure 1a shows the difference in the long‐term mean soil moisture (shaded) and SST (contours) with the estimates from the paleo‐proxy records displayed as colored circles. The colored circles illustrate the SST and hydroclimate conditions of the MCA with respect to modern observations as described by available paleo‐proxy data from around the world (adapted from Seager et al. [2007] )(Pdf-Format, 1,5 MB)[3]. Red (blue) dots represent warmer (cooler) SSTs while green (tan) dots represent wetter (dryer) conditions. The numbers by the dots correspond to those in Table S1 (see auxiliary material).*

The specifics of these records and their limitations are covered in some detail by Herweijer et al. [2007] (Pdf-Format, 3,4 MB)[4] and Seager et al. [2007] and, for some, also by Graham et al. [2007] (Pdf-Format, 1,9 MB)[5]. In order to compare modeled hydroclimate to the various paleo‐proxy records we analyze the  difference in model simulated vertically integrated soil wetness of the root zone (top 0.7 meters), which is significantly correlated with PDSI [Palmer Drought Severity Index, W.v.B.] in observations [Dai et al., 2004][6]. The differing natures of the various proxy reconstructions of hydroclimate, varying from tree rings to flood records, do not allow a quantitative comparison with the model simulation. Instead we are looking for a one sided agreement: conditions either wetter or drier than modern conditions consistently through the medieval period.

Fazit: Eine weitere, wichtige Arbeit in welcher Proxies zur Bestimmung der klimatischen Bedingungen im Mittelalter angeführt werden.

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[1] Seager, R., R. Burgman, Y. Kushnir, A. Clement, E. Cook, N. Naik, and J. Miller (2008), Tropical Pacific forcing of North American medieval megadroughts: Testing the concept with an atmosphere model forced by coral‐reconstructed SSTs, J. Clim., 21, 6175–6190, doi:10.1175/2008JCLI2170.1.

[2] Bar-Matthews, M., Ayalon, A., Kaufman, A., 1998. Middle to late Holocene (6,500 Yr. Period) paleoclimate in the eastern Mediterranean region from the stable isotopic composition of speleothems from Soreq Cave, Israel. In: Issar, A.S., Brown, N. (Eds.), Water, Environment and Society in Times of Climatic Change. Kluwer Academic Publishers, Dordrecht, pp. 203-214.

[3] footnotes 3, 4 and 5 are given with reference to the downloadable PDF. Reason for this is that these works are included in the various Langzeitproxies. Seager, R., N. Graham, C. Herweijer, AL Gordon, Y. Kushnir, and E. Cook (2007), Blueprints for hydro medieval climate, Quat. Sci. Rev., 26 (19-21), 2322-2336, doi: 10.1016/j.quascirev.2007.04.020. Auxiliary materials are available

* in the HTML. doi: 10.1029/2009GL042239.

[4] Herweijer, C., R. Seager, ER Cook and J. Emile-Geay (2007), North American droughts of the last millennium from a gridded network of tree ring data, J. Clim, 20, 1353-1376, doi:. 10.1175/JCLI4042.1.

[5] Graham, N., et al. (2007), Tropical Pacific mid-latitude teleconnections in medieval times, Clim. Change, 83, 241 285, doi: 10.1007/s10584-007-9239-2.

[6] Dai, A., KE Trenberth, and T. Qian (2004), A global dataset of Palmer drought severity index for 1870-2002: Relationship with soil moisture and effects of surface warming, J. Hydrometeorol, 5. , 1117-1130, doi: 10.1175/JHM-386.1.