Global 60?km simulations with CCAM: evaluation over the tropics

A six-member ensemble of 60?km resolution global atmospheric simulations has been performed for studying future climate scenarios of Pacific island nations. The simulations were performed using the CSIRO Conformal Cubic Atmospheric Model (CCAM), driven by bias-corrected sea surface temperatures (SSTs) provided by six Coupled Model Intercomparison Project phase 3 global climate models (GCMs) from the Intergovernmental Panel on Climate Change Fourth Assessment Report for the period 1971–2100. This paper focuses on results for the representation of the current climate in the tropical region, a region where the “cold tongue” problem is apparent in all host GCMs. The SST bias-correction and the fine horizontal resolution employed in the CCAM simulations produce a significant improvement over the host GCMs in the rainfall patterns for the transient seasons March–April–May and September–October–November, and a moderate improvement for December–January–February and June–July–August. CCAM also simulates improved rainfall patterns over the South Pacific Convergence Zone. The performance of other tropical features, such as El Ni?o Southern Oscillation and the Walker circulation, is also evaluated.     

Oscillations in the southern extent of the Indo-Pacific Warm Pool during the mid-Holocene

The Indo-Pacific Warm Pool (IPWP) is thought to play a key role in the propagation and amplification of climate changes through its influence on the global distribution of heat and water vapour. However, little is known about past changes in the size and position of the IPWP. In this study, we use a total of 48 modern and fossil coral records from the Mentawai Islands (Sumatra, Indonesia) and Muschu/Koil Islands (Papua New Guinea) to reconstruct oscillations in the extent of the IPWP since the mid-Holocene. We show that reliable estimates of mean sea surface temperature (SST) can be obtained from fossil corals by using low-resolution Sr/Ca analysis of a suite of corals to overcome the large uncertainties associated with mean Sr/Ca-SST estimates from individual coral colonies. The coral records indicate that the southeastern and southwestern margins of the IPWP were cooler than at present between 5500 and 4300 years BP (1.2 °C ± 0.3 °C) and were similarly cool before 6800 years BP. This mid-Holocene cooling was punctuated by an abrupt, short-lived shift to mean SSTs that were warmer than at present between 6600 and 6300 years BP (1.3 °C ± 0.3 °C), while similarly warm conditions may have also existed after 4300 years BP. We suggest that mid-Holocene cooling at our study sites was related to contractions of the southeastern and southwestern margins of the IPWP, associated with the more northerly position of the Inter-tropical Convergence Zone (ITCZ) that accompanied mid-Holocene strengthening of the Asian summer monsoon. Conversely, intervals of abrupt warming appear to correspond with widespread episodes of monsoon weakening and accompanying southward migrations of the ITCZ that caused the IPWP to expand beyond our coral sites. Intervals of a strengthened Asian monsoon and cooling in the southwestern IPWP during the mid-Holocene appear to correspond with a more positive Indian Ocean Dipole (IOD)-like mean configuration across the tropical Indian Ocean, suggesting that the Asian monsoon–IOD interaction that exists at interannual time scales also persists over centennial to millennial scales. Associated mean changes in the Pacific ENSO modes may have also occurred during the mid-Holocene. The dynamic and inter-connected behaviour of the IPWP with tropical climate systems during the mid-Holocene highlights the fundamental importance of the warm pool region for understanding climate change throughout the tropics and beyond.     

The relationship between synoptic scale airflow direction and daily rainfall: a methodology applied to Devon and Cornwall, South West England

Summary Trans-scale relationships are established between fluctuations in the direction of the geostrophic flow over the British Isles and spatial variations in rainfall over Devon and Cornwall, South West England. The rationale for using such an approach is to provide the basis for assessing changes to the region’s rainfall climatology that may result from possible future enhanced greenhouse effect forced alterations to large-scale wind flow patterns. A new method, the concentration factor (CF), that relates rainfall totals to the frequency of the flow, is applied to investigate spatial variations in rainfall totals at twelve stations in the two counties under eight wind direction groups (N, NE, E, SE, S, SW, W, NW). S and SW flow types are found to produce the highest daily rainfall totals at all locations, with the three easterly groups (NE, E, SE) yielding higher daily precipitation intensities than the maritime NW group. Inter-annual and seasonal variations in daily wind direction – rainfall (WD/R) relationships are then assessed at two contrasting sites in Cornwall (St. Mawgan, Culdrose) using 40 years of data (1957–96). In general, there is a trend over this period toward maritime airflows (S, SW, W, NW) producing higher daily rainfall totals, with the continental groups (N, NE, E, SE) yielding lower totals relative to their frequency of occurrence. The trend toward maritime airflows producing higher rainfall totals is in line with recent trends in the North Atlantic Oscillation (NAO). Notable seasonal variations in WD/R relationships over Cornwall are interpreted in terms of the location’s exposure to the prevailing wind, sea temperature variations and the orography of the South West Peninsula. Received October 23, 2000/Revised February 2, 2001     

Diagenesis and geochemistry of porites corals from Papua New Guinea: Implications for paleoclimate reconstruction

Coral proxy records of sea surface temperature (SST) and hydrological balance have become important tools in the field of tropical paleoclimatology. However, coral aragonite is subject to post-depositional diagenetic alteration in both the marine and vadose environments. To understand the impact of diagenesis on coral climate proxies, two mid-Holocene Porites corals from raised reefs on Muschu Island, Papua New Guinea, were analysed for Sr/Ca, δ¹⁸O, and δ¹³C along transects from 100% aragonite to 100% calcite. Thin-section analysis showed a characteristic vadose zone diagenetic sequence, beginning with leaching of primary aragonite and fine calcite overgrowths, transitional to calcite void filling and neomorphic, fabric selective replacement of the coral skeleton. Average calcite Sr/Ca and δ¹⁸O values were lower than those for coral aragonite, decreasing from 0.0088 to 0.0021 and −5.2 to −8.1‰, respectively. The relatively low Sr/Ca of the secondary calcite reflects the Sr/Ca of dissolving phases and the large difference between aragonite and calcite Sr/Ca partition coefficients. The decrease in δ¹⁸O of calcite relative to coral aragonite is a function of the δ¹⁸O of precipitation. Carbon-isotope ratios in secondary calcite are variable, though generally lower relative to aragonite, ranging from −2.5 to −10.4%. The variability of δ¹³C in secondary calcite reflects the amount of soil CO₂ contributing ¹³C-depleted carbon to the precipitating fluids. Diagenesis has a greater impact on Sr/Ca than on δ¹⁸O; the calcite compositions reported here convert to SST anomalies of 115°C and 14°C, respectively. Based on calcite Sr/Ca compositions in this study and in the literature, the sensitivity of coral Sr/Ca-SST to vadose-zone calcite diagenesis is 1.1 to 1.5°C per percent calcite. In contrast, the rate of change in coral δ¹⁸O-SST is relatively small (−0.2 to 0.2°C per percent calcite). We show that large shifts in δ¹⁸O, reported for mid-Holocene and Last Interglacial corals with warmer than present Sr/Ca-SSTs, cannot be caused by calcite diagenesis. Low-level calcite diagenesis can be detected through X-ray diffraction techniques, thin section analysis, and high spatial resolution sampling of the coral skeleton and thus should not impede the production of accurate coral paleoclimate reconstructions.     

Negotiating nature: exploring discourse through small group research

The full potential of discussion groups to further geographic interest in the relationship between discourse, individual and society can still be developed further. This paper briefly reviews previous applications of discussion group methodologies before suggesting a new discourse-centred approach that explores how broad social discourses impact everyday conversations. The approach is demonstrated through a case study involving supporters of environmental movements in Australia. It is concluded that small groups can be used in new ways that provide important methodologically unique insights into the reception of transient, but powerful, discourses upon everyday lives.     

Regional climate modelling

Summary Regional climate modelling is becoming increasingly popular. The most common technique employs high resolution limited-area models to economically produce detaited climatologies for selected regions. A short review is presented of the underlying principles, recent simulations limitations of the method and future prospects.With 4 Figures     

Synoptic typing and its application to the investigation of weather air pollution relationships,Birmingham, United Kingdom

Summary Principal components analysis and cluster analysis are used to derive airmass types based on surface meteorological data for the Birmingham area. UK. Airmass types are analysed in terms of their climatological, meteorological and air pollution characteristics. Continental anticyclonic airmass types are identified as producing high pollution concentration events, whereas, maritime cyclonic types, characterised by strong westerly flows are associated with low levels of atmospheric pollutants.With 3 Figures     

Theoretical current and future indoor thermal preferendum for equatorial western and tropical South Pacific

Summary Current and future indoor thermal preferendum are estimated for a number of locations in the equatorial western and tropical South Pacific region. Current warm season mean monthly temperatures, for the majority of the study area, are in excess of predicted indoor thermal preferendum, indicating the need for either passive, or active cooling, of indoor environments. Comparison of accepted warm season thermostat settings, with theoretical preferred indoor temperatures, suggests that current indoor environments may be over airconditioned. Climatic change will lead to a divergence of environmental and preferred indoor temperatures. As a consequence, increased levels of airconditioning may be required. The possible energy savings that may result, due to the application of location specific thermostat settings, in line with preferred indoor thermal preferendum, are discussed for a Greenhouse forced warmer western equatorial and tropical South Pacific.With 7 Figures