Seasonal prediction skill of ECMWF System 4 and NCEP CFSv2 retrospective forecast for the Northern Hemisphere Winter

The seasonal prediction skill for the Northern Hemisphere winter is assessed using retrospective predictions (1982–2010) from the ECMWF System 4 (Sys4) and National Center for Environmental Prediction (NCEP) CFS version 2 (CFSv2) coupled atmosphere–ocean seasonal climate prediction systems. Sys4 shows a cold bias in the equatorial Pacific but a warm bias is found in the North Pacific and part of the North Atlantic. The CFSv2 has strong warm bias from the cold tongue region of the eastern Pacific to the equatorial central Pacific and cold bias in broad areas over the North Pacific and the North Atlantic. A cold bias in the Southern Hemisphere is common in both reforecasts. In addition, excessive precipitation is found in the equatorial Pacific, the equatorial Indian Ocean and the western Pacific in Sys4, and in the South Pacific, the southern Indian Ocean and the western Pacific in CFSv2. A dry bias is found for both modeling systems over South America and northern Australia. The mean prediction skill of 2 meter temperature (2mT) and precipitation anomalies are greater over the tropics than the extra-tropics and also greater over ocean than land. The prediction skill of tropical 2mT and precipitation is greater in strong El Nino Southern Oscillation (ENSO) winters than in weak ENSO winters. Both models predict the year-to-year ENSO variation quite accurately, although sea surface temperature trend bias in CFSv2 over the tropical Pacific results in lower prediction skill for the CFSv2 relative to the Sys4. Both models capture the main ENSO teleconnection pattern of strong anomalies over the tropics, the North Pacific and the North America. However, both models have difficulty in forecasting the year-to-year winter temperature variability over the US and northern Europe.     

Assessment of drought over the past two millennia using near-shore sediment cores from a Canadian boreal lake

Lack of long-term studies on drought in the boreal region of northwest Ontario limits our ability to assess the vulnerability of this region to climate change. We investigated changes in diatoms, scaled chrysophytes, and sedimentary pigments in two near-shore cores from Gall Lake to infer limnological and water-level changes over the last two millennia. The two coring locations, at modern water depths of 7.5 and 11.5 m, were selected to contrast inferences for past lake level based on distance from the modern water-depth boundary between predominantly benthic and planktonic diatom assemblages in surface sediments (6.0 m). Diatom-inferred depth inferences were more variable in the core from 7.5-m water depth, consistent with the hypothesis that the greatest changes occurred at water depths closest to the benthic:planktonic boundary. Both sites revealed a pronounced drought from ~AD 950 to 1300, synchronous with the medieval climate anomaly (MCA). This finding suggests a northeast expansion of the arid MCA into northwest Ontario, extending the known spatial extent of this megadrought. Scaled chrysophytes and sedimentary pigments suggest a recent increase in thermal stratification. Our findings indicate this region is more susceptible to changes in moisture than was previously suspected based on the instrumental record for the past century.     

The lunar rock and mineral characterization consortium: Deconstruction and integrated mineralogical,petrologic, and spectroscopic analyses of mare basalts

The lunar rock and mineral characterization consortium (LRMCC) has conducted coordinated mineralogy/petrography/spectroscopy analyses of a suite of pristine lunar basalts. Four basalt slabs (two low‐Ti, two high‐Ti) and paired thin sections were analyzed. Thin sections were analyzed for mineralogy/petrography, while the slabs were used to prepare particulate separates of major mineral phases and bulk samples. Mineral separates and particulate bulk samples were crushed to controlled grain sizes and their reflectance spectra measured in the NASA RELAB at Brown University. The resulting data set provides an essential foundation for spectral mixing models, offers valuable endmember constraints for space weathering analyses, and represents critical new ground truth results for lunar science and exploration efforts.     

Lead analysis of sediment cores from seven Connecticut lakes

Lead analyses were performed on sediment cores from seven Connecticut lakes by dilute acid leaching. The absolute concentrations of lead varied from core to core, but the lead profiles were similar in all of the cores, and each depicted a point where the concentration of lead sharply increased above background levels. The background lead concentrations observed in the bottom portions of the cores ranged from 12-54 g Pb/g sediment with a mean of 30 g Pb/g, and increased to a mean maximum of 310 g Pb/g. In six of the lakes significant increases above background levels were not noted until between 1924 and 1952, suggesting that, at least for Connecticut lakes, the point in a lake sediment core where the concentration of lead began to increase was after ca. 1924, and on average about 1930. Lead concentrations declined in the surface sediments of only three of the lakes, mostly since the 1980's, and presumably in response to the phasing out of leaded gasoline. However, significant declines in lead concentrations were not observed in the remaining cores, possibly due to increased motor vehicle use within the airshed of the lakes and/or changes in the export of lead to the lakes from their watersheds.     

Simultaneous optical polarimetry and X-ray observations of the magnetic CV CP Tuc (AX J2315−592)

CP Tuc (AX J2315–592) shows a dip in X-rays which lasts for approximately half the binary orbit and is deeper in soft X-rays compared with hard X-rays. It has been proposed that this dip is due to the accretion stream obscuring the accretion region from view. If CP Tuc were a polar, as has been suggested, then the length of such a dip would make it unique amongst polars since in those polars in which a dip is seen in hard X-rays the dip lasts for only 0.1 of the orbit. We present optical polarimetry and RXTE observations of CP Tuc which show circular polarization levels of ∼10 per cent and find evidence for only one photometric period. These data confirm CP Tuc as a polar. Our modelling of the polarization data implies that the X-ray dip is due to the bulk of the primary accretion region being self-eclipsed by the white dwarf. The energy dependence of the dip is due to a combination of this self-eclipse and also the presence of an X-ray temperature gradient over the primary accretion region.     

Experimental determination of photostability and fluorescence‐based detection of PAHs on the Martian surface

Abstract– Even in the absence of any biosphere on Mars, organic molecules, including polycyclic aromatic hydrocarbons (PAHs), are expected on its surface due to delivery by comets and meteorites of extraterrestrial organics synthesized by astrochemistry, or perhaps in situ synthesis in ancient prebiotic chemistry. Any organic compounds exposed to the unfiltered solar ultraviolet spectrum or oxidizing surface conditions would have been readily destroyed, but discoverable caches of Martian organics may remain shielded in the subsurface or within surface rocks. We have studied the stability of three representative polycyclic aromatic hydrocarbons (PAHs) in a Mars chamber, emulating the ultraviolet spectrum of unfiltered sunlight under temperature and pressure conditions of the Martian surface. Fluorescence spectroscopy is used as a sensitive indicator of remaining PAH concentration for laboratory quantification of molecular degradation rates once exposed on the Martian surface. Fluorescence‐based instrumentation has also been proposed as an effective surveying method for prebiotic organics on the Martian surface. We find the representative PAHs, anthracene, pyrene, and perylene, to have persistence half‐lives once exposed on the Martian surface of between 25 and 60 h of noontime summer UV irradiation, as measured by fluorescence at their peak excitation wavelength. This equates to between 4 and 9.6 sols when the diurnal cycle of UV light intensity on the Martian surface is taken into account, giving a substantial window of opportunity for detection of organic fluorescence before photodegradation. This study thus supports the use of fluorescence‐based instrumentation for surveying recently exposed material (such as from cores or drill tailings) for native Martian organic molecules in rover missions.     

Impact of stratospheric variability on tropospheric climate change

An improved stratospheric representation has been included in simulations with the Hadley Centre HadGEM1 coupled ocean atmosphere model with natural and anthropogenic forcings for the period 1979–2003. An improved stratospheric ozone dataset is employed that includes natural variations in ozone as well as the usual anthropogenic trends. In addition, in a second set of simulations the quasi biennial oscillation (QBO) of stratospheric equatorial zonal wind is also imposed using a relaxation towards ERA-40 zonal wind values. The resulting impact on tropospheric variability and trends is described. We show that the modelled cooling rate at the tropopause is enhanced by the improved ozone dataset and this improvement is even more marked when the QBO is also included. The same applies to warming trends in the upper tropical troposphere which are slightly reduced. Our stratospheric improvements produce a significant increase of internal variability but no change in the positive trend of annual mean global mean near-surface temperature. Warming rates are increased significantly over a large portion of the Arctic Ocean. The improved stratospheric representation, especially the QBO relaxation, causes a substantial reduction in near-surface temperature and precipitation response to the El Chichón eruption, especially in the tropical region. The winter increase in the phase of the northern annular mode observed in the aftermath of the two major recent volcanic eruptions is partly captured, especially after the El Chichón eruption. The positive trend in the southern annular mode (SAM) is increased and becomes statistically significant which demonstrates that the observed increase in the SAM is largely subject to internal variability in the stratosphere. The possible inclusion in simulations for future assessments of full ozone chemistry and a gravity wave scheme to internally generate a QBO is discussed.     

The palaeolimnology of Lake Fidler, a meromictic lake in south-west Tasmania and the significance of recent human impact

Three meromictic lakes in the World Heritage Area of south-west Tasmania possess unusual microbiological communities. Their meromixis is maintained by periodic incursions of brackish water from the nearby Gordon River which, in its lower reaches, is a salt-wedge estuary. In 1977 the construction of a dam in the middle reaches of the river restricted penetration of the salt-wedge and meromixis rapidly declined in all three lakes. A palaeolimnological study was carried out on one of the lakes, Lake Fidler, firstly to determine the history of meromixis and its associated microbiological communities, and secondly to assess whether the recent and rapid decline of meromixis is inconsistent with natural rates of development of the Gordon River meromictic lakes. One part of this study included the analysis of the stratigraphy of fossil diatoms from a 17-metre sediment core dating back 8000 yrs. Detrended Correspondence Analysis and Analog Matching were used to compare diatom species assemblages in core samples with diatom samples from a reference dataset consisting of a selection of lake and river sites in the lower Gordon River valley. Five distinct stratigraphic zones were identified in the core. These zones indicated specific stages in the development of the Gordon River lakes from river backwaters to ectogenically-maintained meromictic lakes which will, finally, become terrestrialised by encroaching rainforest. The onset of a stratified water column was identified by the emergence of a dominant freshwater algal flora which suggested that the lake had developed a mixolimnion and become meromictic ca. 2070 ± 50 ¹⁴C yrs ago. In the context of this long history of meromixis, the rapid demise in meromictic stability following construction of the dam is judged to be inconsistent with natural rates of development. The palaeolimnological studies, of which this paper is one part, prompt recommendations for a management strategy to prevent the further decay of these meromictic lakes in the World Heritage Area.