A land surface model incorporated with soil freeze/thaw and its application in GAME/Tibet

Hu, HP Ye, BS Zhou, YH Tian, FQ

SCIENCE IN CHINA SERIES D-EARTH SCIENCES 49:12 1311-1322

Land surface process is of great importance in global climate change, moisture and heat exchange in the interface of the earth and atmosphere, human impacts on the environment and ecosystem, etc. Soil freeze/thaw plays an important role in cold land surface processes. In this work the diurnal freeze/thaw effects on energy partition in the context of GAME/Tibet are studied. A sophisticated land surface model is developed, the particular aspect of which is its physical consideration of soil freeze/thaw and vapor flux. The simultaneous water and heat transfer soil sub-model not only reflects the water flow from unfrozen zone to frozen fringe in freezing/thawing soil, but also demonstrates the change of moisture and temperature field induced by vapor flux from high temperature zone to low temperature zone, which makes the model applicable for various circumstances. The modified Picard numerical method is employed to help with the water balance and convergence of the numerical scheme. Finally, the model is applied to analyze the diurnal energy and water cycle characteristics over the Tibetan Plateau using the Game/Tibet datasets observed in May and July of 1998. Heat and energy transfer simulation shows that: (i) There exists a negative feedback mechanism between soil freeze/thaw and soil temperature/ground heat flux; (ii) during freezing period all three heat fluxes do not vary apparently, in spite of the fact that the negative soil temperature is higher than that not considering soil freeze; (iii) during thawing period, ground heat flux increases, and sensible heat flux decreases, but latent heat flux does not change much; and (iv) during freezing period, soil temperature decreases, though ground heat flux increases.

melatonin:methods | /neutral/methods | 128

Interhemispheric anti-phasing of rainfall during the last glacial period

Wang, XF Auler, AS Edwards, RL Cheng, H Ito, E Solheid, M

QUATERNARY SCIENCE REVIEWS 25:23-24 3391-3403

We have obtained a high-resolution oxygen isotopic record of cave calcite from Caverna Botuvera (27 degrees 13’S, 49 degrees 09’W), southern Brazil, which covers most of the last 36 thousand years (ka), with an average resolution of a few to several decades. The chronology was determined with 46 U/Th ages from two stalagmites. Tests for equilibrium conditions show that oxygen isotopic variations are primarily caused by climate change. We interpret our record in terms of meteoric precipitation changes, hence the variability of South American Monsoon (SAM) intensity. The oxygen isotopic profile broadly follows local insolation changes and shows clear millennial-scale variations during the last glacial period with amplitudes as large as 3 parts per thousand but with smaller centennial-scale shifts (< 1 parts per thousand) during the Holocene. The overall record is strikingly similar to, but strongly anti-correlated with, a number of records from the Northern Hemisphere. We compared our record to other precisely dated contemporaneous records from Hulu Cave eastern China. Minima in 6180 (wet periods, intense SAM) at our site are synchronous with maxima in delta O-18 (dry periods, weak East Asian Monsoon, EAM) in eastern China (within precise dating errors) and vice versa. This anti-phased precipitation relationship between two low-latitude locations may be interhemispheric in extent, based on comparison with records from other sites. Precipitation anti-phasing may be related to north-south shifts in the mean position of the intertropical convergence zone (ITCZ) and asymmetry in Hadley circulation in two hemispheres, associated not with seasonal changes as observed today, but with millennial-scale climate shifts. The millennial-scale atmospheric see-saw patterns that we observe could have important controls and feedbacks on climate within hemispheres because of water vapor’s greenhouse properties. (c) 2006 Elsevier Ltd. All rights reserved.

melatonin:paleo | /neutral/paleo | 071

Seasonal-to-decadal predictability and prediction of South American climate

Nobre, P Marengo, JA Cavalcanti, IFA Obregon, G Barros, V Camilloni, I Campos, N Ferreira, AG

JOURNAL OF CLIMATE 19:23 5988-6004

The dynamical basis for seasonal to decadal climate predictions and predictability over South America is reviewed. It is shown that, while global tropical SSTs affect both predictability and predictions over South America, the current lack of SST predictability over the tropical Atlantic represents a limiting factor to seasonal climate predictions over some parts of the continent. The model’s skill varies with the continental region: the highest skill is found in the “Nordeste” region and the lowest skill over southeastern Brazil. It is also suggested that current two-tier approaches to predict seasonal climate variations might represent a major limitation to forecast coupled ocean-atmosphere phenomena like the South Atlantic convergence zone. Also discussed are the possible effects of global climate change on regional predictability of seasonal climate.

melatonin:methods | /neutral/methods | 119