Importance of the mixed-phase cloud distribution in the control climate for assessing the response of clouds to carbon dioxide increase: a multi-model study

We have conducted a multi-model intercomparison of cloud-water in five state-of-the-art AGCMs run for control and doubled carbon dioxide climates. The most notable feature of the differences between the control and doubled carbon dioxide climates is in the distribution of cloud-water in the mixed-phase temperature band. The difference is greatest at mid and high latitudes. We found that the amount of cloud ice in the mixed phase layer in the control climate largely determines how much the cloud-water distribution changes for the doubled carbon dioxide climate. Therefore evaluation of the cloud ice distribution by comparison with data is important for future climate sensitivity studies. Cloud ice and cloud liquid both decrease in the layer below the melting layer, but only cloud liquid increases in the mixed-phase layer. Although the decrease in cloud-water below the melting layer occurs at all latitudes, the increase in cloud liquid in the mixed-phase layer is restricted to those latitudes where there is a large amount of cloud ice in the mixed-phase layer. If the cloud ice in the mixed-phase layer is concentrated at high latitudes, doubling of carbon dioxide might shift the center of cloud water distribution poleward which could decrease solar reflection because solar insolation is less at higher latitude. The magnitude of this poleward shift of cloud water appears to be larger for the higher climate sensitivity models, and it is consistent with the associated changes in cloud albedo forcing. For the control climate there is a clear relationship between the differences in cloud-water and relative humidity between the different models, for both magnitude and distribution. On the other hand the ratio of cloud ice to cloud-water follows the threshold temperature which is determined in each model. Improved measurements of relative humidity could be used to constrain the modeled representation of cloud water. At the same time, comparative analysis in global cloud resolving model simulations is necessary for further understanding of the relationships suggested in this paper.     

Comparison of TL multiple aliquot, single grain GLSL SAR and C-14 ages for the Puritjarra, Australia, rock shelter

We report single-grain quartz luminescence ages for the Puritjarra rock shelter, with the aim of resolving an apparent discrepancy between ages obtained by ¹⁴C and a variety of luminescence methods, previously reported. Ages now found at all depths to 75 cm (ages to 30 ka) can be interpreted as largely resolving the differences. This implied caveat arises because single-grain methods are statistically inefficient. As a consequence, a degree of interpretation is inevitable in analysing the data. The emphasis in the present paper is an analysis making use of weighted histograms. The measurements by single grain OSL and ¹⁴C, including ABOX–SC, taken together, can be regarded as compatible. They indicate human occupation of the Puritjarra rock shelter at least as early as 30 ka BP.     

GCM intercomparison of global cloud regimes: present-day evaluation and climate change response

The radiative feedback from clouds remains the largest source of variation in climate sensitivity amongst general circulation models (GCMs). A cloud clustering methodology is applied to six contemporary GCMs in order to provide a detailed intercomparison and evaluation of the simulated cloud regimes. By analysing GCMs in the context of cloud regimes, processes related to particular cloud types are more likely to be evaluated. In this paper, the mean properties of the global cloud regimes are evaluated, and the cloud response to climate change is analysed in the cloud-regime framework. Most of the GCMs are able to simulate the principal cloud regimes, however none of the models analysed have a good representation of trade cumulus in the tropics. The models also share a difficulty in simulating those regimes with cloud tops at mid-levels, with only ECHAM5 producing a regime of tropical cumulus congestus. Optically thick, high top cloud in the extra-tropics, typically associated with the passage of frontal systems, is simulated considerably too frequently in the ECHAM5 model. This appears to be a result of the cloud type persisting in the model after the meteorological conditions associated with frontal systems have ceased. The simulation of stratocumulus in the MIROC GCMs is too extensive, resulting in the tropics being too reflective. Most of the global-mean cloud response to doubled CO₂ in the GCMs is found to be a result of changes in the cloud radiative properties of the regimes, rather than changes in the relative frequency of occurrence (RFO) of the regimes. Most of the variance in the global cloud response between the GCMs arises from differences in the radiative response of frontal cloud in the extra-tropics and from stratocumulus cloud in the tropics. This variance is largely the result of excessively high RFOs of specific regimes in particular GCMs. It is shown here that evaluation and subsequent improvement in the simulation of the present-day regime properties has the potential to reduce the variance of the global cloud response, and hence climate sensitivity, amongst GCMs. For the ensemble of models considered in this study, the use of observations of the mean present-day cloud regimes suggests a potential reduction in the range of climate sensitivity of almost a third. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Risk analysis of possible impacts of climate change on South Australian wheat production

This study presents a model-based risk assessment of wheat production under projected climate change by 2080 in eight locations of South Australia. The vulnerability of wheat production under future climate change was quantitatively evaluated via a risk analysis in which the identification of critical yield thresholds applies. Research results show that risk (conditional probability of not exceeding the critical yield thresholds) increased more or less across all locations under the most likely climate change. Wheat production in drier areas such as Minnipa, Orroroo and Wanbi will not be economically viable under the most likely climate change. Intensive studies on adaptation are now required.     

What explains agricultural performance: climate normals or climate variance?

This paper measures the influence of climate normals (average long-term surface wetness and temperature) and interannual climate variance on farms in the United States and Brazil using satellite data. The paper finds that just climate normals or just climate variance variables can explain both net revenues and how much land is used for cropland. However, because they are correlated with each other, it is important to include both normals and variance in the same statistical model to get accurate measures of their individual contribution to farm outcomes. In general, higher climate variance increases the probability that land is used for cropland in both countries and higher temperatures reduce both cropland and land values. Other annual effects were not consistent across the two countries.     

Measuring Polar-Angle Errors in Imaged Helioseismology

A sixteen-day sequence of GONG full-disk Dopplergrams was computer-rotated by plus and minus 1° with respect to the midpoint of the equator to produce two additional data sets simulating errors in the instrumental alignment with the rotation axis. The unrotated and two rotated data sets were then reduced to produce tables of mode linewidths and line-peak powers. The line characteristics of the two rotated sets were compared to the unrotated set for 20 l 120. It was found that the linewidths increased as much as 55% and the line-peak powers decreased as much as 17%, with increasing l. These results are in good agreement with an earlier model (Kennedy, 1997). Differential linewidths studies indicated that the GONG instrument-network rotation-axis alignment was within 0.048° ± 0.040° during the period of the observation.     

Interplanetary scintillation observations of interaction regions in the solar wind

Co-rotating interaction regions (CIRs) between fast and slow streams of plasma are a prominent feature of the solar wind. Measurements of interplanetary scintillation (IPS) using the three widely separated antennas of the EISCAT facility have been used to detect the compression regions at the leading edges of interaction regions and to determine the location and velocity of the structure. Observations show that interaction regions have developed as close to the Sun as 25–30 solar radii, a result supported by theoretical modelling which shows that the conditions needed for CIRs to develop exist inside 30 solar radii.     

Post-collisional volcanism in a sinking slab setting—crustal anatectic origin of pyroxene-andesite magma, Caldear Volcanic Group, Neogene Alborán volcanic province, southeastern Spain

Caldear Volcanic Group (CVG), a stratigraphically well defined, calc-alkaline rock complex within S^a de Gata in the eastern part of the Alpine Betic mountain chain, S Spain, consists of three distinct formations: Hernández pyroxene andesites, Bujo hornblende-bearing pyroxene andesites and Viuda hornblende-bearing pyroxene dacites–rhyolites. The letter rock formation may have developed through crystal fractionation of mainly plagioclase and pyroxenes, however there is no direct relation between two formations. CVG has a domainal structure with a northeastern domain where Hernández formation is overlain by Bujo formation while Viuda formation is absent, and a southwestern domain where Viuda formation forms the only fractionate after Hernández formation. Hernández parent magma is thought generated through crustal anatexis by dehydration melting of a predominantly amphibolitic source rock complex which was formed by metamorphism from c. 500 Ma volcano-sedimentary parent material. The domainal structure of CVG is explained by compositional variation within this protogenetic complex. Single crystal U–Pb ages of c. 500 Ma to 1800 Ma for inherited zircon support the presence of clastic material of Proterozoic derivation within the original volcano-sedimentary complex. Regional study of syn-collisional rock formations (Alpine nappe complexes) indicate that the collisional tectonic stage in the Betic-Rif orogenic belt took place rather early (25–30 Ma?) and was followed by a stage of rapid regional rock uplift, fast cooling (c. 500°C/my) and extensional tectonics in the period 22–17 Ma. This later tectonic stage was set into motion by slab break-off which set the stage for a high temperature regime in the overlying lithosphere, providing the framework for the crustal melting and magma production responsible for the calc-alkaline rocks of Alborán volcanic province. Miocene zircon with ages ranging from c. 17 to 11 Ma indicate a rather protracted magmatic development prior to eruption at c. 11 Ma. Post-collisional character of Caldear Volcanic Group thus seems well established.     

Precambrian tidal and glacial clastic deposits: implications for Precambrian Earth–Moon dynamics and palaeoclimate

Over the past decade the study of Precambrian clastic tidal rhythmites — stacked laminae of sandstone, siltstone and mudstone that display periodic variations in thickness reflecting a strong tidal influence on sedimentation — has provided accurate palaeotidal and palaeorotational data. Palaeotidal records obtained from tidal rhythmites may be systematically abbreviated, however, and derived periods and frequencies can be misleading. The validity of such values, including past length of day, can be assessed by testing for internal self-consistency through application of the laws of celestial mechanics. Such a test supports the estimated length of day of h derived from the late Neoproterozoic (620 Ma) Elatina–Reynella rhythmites in South Australia, and the indicated mean rate of lunar retreat of cm/year since 620 Ma. The validity of estimated lengths of day obtained from other Precambrian tidal rhythmites remain unverified because the data sets contain only one primary value directly determined from the rhythmites. The Elatina–Reynella data militate against significant Earth expansion at least since 620 Ma, and suggest that the free nutation or ‘tipping' of the Earth's fluid core has undergone a resonance with the Earth's annual forced nutation since the Neoproterozoic. Glaciogenic deposits are readily distinguishable from ejecta resulting from impacts with Earth-crossing bodies. Palaeomagnetic data, based on the geocentric axial dipole model for the geomagnetic field, indicate that Neoproterozoic and Palaeoproterozoic glaciation and cold climate near sea level occurred in low palaeolatitudes. This enigmatic finding may imply global glaciation or an increased obliquity of the ecliptic, and is relevant to modelling the effect of ice sheet formation on the Earth's obliquity history by obliquity–oblateness feedback mechanisms. Through multidisciplinary studies, clastic sedimentology and geophysics together can make substantial contributions to understanding Precambrian Earth–Moon dynamics and global palaeoenvironments.     

The spatial structure of the dayside ionospheric trough

Tomographic imaging provides a powerful technique for obtaining images of the spatial distribution of ionospheric electron density at polar latitudes. The method, which involves monitoring radio transmissions from the Navy Navigation Satellite System at a meridional chain of ground receivers, has particular potential for complementing temporal measurements by other observing techniques such as the EISCAT incoherent-scatter radar facility. Tomographic reconstructions are presented here from a two-week campaign in November 1995 that show large-scale structuring of the polar ionosphere. Measurements by the EISCAT radar confirm the authenticity of the technique and provide additional information of the plasma electron and ion temperatures. The dayside trough, persistently observed at high latitudes during a geomagnetically quiet period but migrating to lower latitudes with increasing activity, is discussed in relationship to the pattern of the polarcap convection.