Potential effects of climatic change on the distribution of Tetraclinis articulata, an endemic tree from arid Mediterranean ecosystems

South-eastern Spain is a key area for assessing the effects of climate change on biodiversity since it presents an ecotone between the Mediterranean biome and the subtropical shrublands of arid lands. The forests of Tetraclinis articulata constitutes an especially relevant case. A species distribution model has been developed, regionalised climate change scenarios for South-eastern Spain were generated and expected changes in the suitability area of this species were estimated under B2 and A2 SRES scenarios for the time slice 2020–2050. Moreover, land use in the present and future potential habitat has been analysed. The high sensitivity of T. articulata is expressed not only as effects of climate change in the near future when compared to the present-day situation but also in the remarkable differences under scenarios B2 and A2. Under scenario B2 the suitable area for T. articulata would expand six-fold whereas under A2 the potential habitat would disappear from its present-day distribution and would move to a small area in the interior mountains. Under scenario B2 the future potential habitat in the coastal location would include enough area of shrublands, the main effective habitat of the species. Moreover, the present and future potential habitat partially overlaps, which facilitates the species migration. On the contrary, in the interior potential habitat the land use is less favourable for the effective habitat, the actual and future potential habitat do not overlap and the low dispersal capabilities of the species prevents natural migration to the interior to be expected.     

Imaging Spectroscopy of a White-Light Solar Flare

We report observations of a white-light solar flare (SOL2010-06-12T00:57, M2.0) observed by the Helioseismic Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The HMI data give us the first space-based high-resolution imaging spectroscopy of a white-light flare, including continuum, Doppler, and magnetic signatures for the photospheric Fe i line at 6173.34 Å and its neighboring continuum. In the impulsive phase of the flare, a bright white-light kernel appears in each of the two magnetic footpoints. When the flare occurred, the spectral coverage of the HMI filtergrams (six equidistant samples spanning ±172 mÅ around nominal line center) encompassed the line core and the blue continuum sufficiently far from the core to eliminate significant Doppler crosstalk in the latter, which is otherwise a possibility for the extreme conditions in a white-light flare. RHESSI obtained complete hard X-ray and γ-ray spectra (this was the first γ-ray flare of Cycle 24). The Fe i line appears to be shifted to the blue during the flare but does not go into emission; the contrast is nearly constant across the line profile. We did not detect a seismic wave from this event. The HMI data suggest stepwise changes of the line-of-sight magnetic field in the white-light footpoints.     

Extreme normalised residuals of daily temperatures in Catalonia (NE Spain): sampling strategies, return periods and clustering process

Extreme normalised residuals, defined as departures from the average values, of 65 daily maximum, T _max, and minimum, T _min, temperature series recorded in Catalonia (NE Spain) during 1950–2004 are analysed. Similarly to the sampling strategies applied to long dry spells, the partial duration series (PDS) offer some advantages in comparison with the annual extreme series. Instead of using a common percentile threshold for all temperature series, PDS are chosen according to the mean excess plot procedure. Series of extreme residuals are modelled, in terms of the L-moments formulation, by the generalised Pareto distribution. Extreme residuals of T _max and T _min are estimated for return periods ranging from 2 to 50 years and their spatial distribution is represented for selected return periods of 2, 5, 10, 25 and 50 years. Two daily extreme temperatures events, a hot episode (in August) and a cold episode (in February), are simulated taking into account the average T _max (T _min) for a day in August (February), their standard deviations and the extremes for a 50-year return period. Both simulations are compared with outstanding real episodes recorded on August 13th 2003 and February 11th 1956. Additionally, a spatial regionalisation of Catalonia in several clusters, in terms of the extreme residuals for return periods from 2 to 50 years, is done. A principal component analysis is applied to the extreme residual curves characterising every temperature series and, using as variables the principal components, the regionalisation is obtained by applying the average linkage clustering algorithm. Finally, each cluster is characterised by its average extreme residual curve for return periods ranging from 2 to 50 years at 1-year interval.     

Late Mesozoic and Cenozoic palaeomagnetism of Australia–II. Implications for geomagnetism and true polar wander

Summary. New palaeomagnetic results from Australia indicate that throughout the Cenozoic era the continent lay further south than suggested by hot-spot data. Moreover, while hot spots give a uniform rate of drift during most of the Cenozoic, the drift rate obtained from apparent polar wander varies considerably.
The discrepancies between the palaeomagnetic and hot-spot results are analysed by comparing the Australian data with those of Europe and the central Pacific. The analysis suggests that the discrepancies are due to: (1) departures of the Earth's magnetic field from the geocentric axial dipole model, and (2), either true polar wander or a non-axial inclined dipole component. It is found that since the mid-Tertiary the dominant non-dipole component has been a quadrupole, and that during this period both the quadrupolar field and the true polar displacement/non-axial dipole component decreased progressively. During the Quaternary, and also at the earliest Tertiary, the non-dipole components appear to have been moderate or small.
The comparison of data sets demonstrates that considerable errors may be incurred when Cenozoic, and presumably earlier, poles from one geographic region are used to derive those of another, widely separated, region. The results also imply that absolute plate velocities estimated from palaeomagnetic data can contain substantial errors, and that hot-spot data may need significant adjustments for true polar wander to yield correct palaeolatitudes.
Finally, the new early Tertiary pole for Australia is used in conjunction with updated early Tertiary poles from other lithospheric plates to reapply the McKenzie test for true polar wander. The results indicate a small true polar displacement since the beginning of the Tertiary. The amount and direction of the displacement, however, differ from those generally obtained from hot-spot data.     

A quantitative comparison of vector magnetic field measurement and analysis techniques

We make a quantitative comparison between spectral vs filter measurement and analysis techniques for extraction of solar vector magnetic fields from polarimetric data using as a basis the accurately calibrated, high angular resolution Stokes profile data from the Advanced Stokes Polarimeter. It is shown that filter-based measurements deliver qualitative images of the field alignment for sunspots that are visually similar to images derived from the more detailed analysis of the Stokes profiles. However, quantitative comparison with least-squares fits to the full Stokes profiles show that both the strength of the field predicted by the filter-based analysis and its orientation contain substantial errors. These errors are largest for plage regions outside of sunspots, where the field strengths are inferred to be only a fraction of their true values, and errors in the orientation of 40–50° are common. Within sunspots, errors of 20° are commonplace. The greatest source of these errors is the inability of the filter-based measurements to account for the small fill fraction of magnetic fields or, equivalently, scattered light in the instrument, which reduce the degree of polarization. The uncertainties of the full profile fitting methods are also discussed, along with the errors introduced by coarser wavelength sampling of the observed Stokes profiles. The least-squares fitting procedure operates best when the profiles are sampled at least as frequently as one Doppler width of the line.On leave from the Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

The instrumental polarization of a Gregory-Coudé telescope

We calculate a theoretical model of the polarization properties of a Gregory-Coudé telescope to predict the behaviour of the German Gregory-Coudé Telescope installed at the Observatorio del Teide (Spain). Measurements of the real effects produced by this telescope acting upon light of known polarization are compared with the model. We estimate an uncertainty in its predictions of about 10%, which is produced by the uncertainties of the (complex) refractive index of the metallic layers covering the mirrors. The paper concludes by briefly considering the way in which the plain telescope changes the Stokes' profiles.     

High-pressure,low-temperature metamorphism in Alpujarride Units of southeastern Betics (Spain)Métamorphisme de haute pression et basse température dans les unités Alpujarrides du Sud-Est de la cordillère Bétique (Espagne)

We present the first occurrences of high-pressure, low-temperature ferro-magnesiocarpholite-bearing mineral assemblages associated to quartz segregations in the Alpujarride units of southeastern Betics (Sierra de Almagro, Sierra de los Pinos and Sierra Cabrera). Thermobarometric results show that the carpholite-bearing rocks underwent the same P–T conditions in the three outcrops, i.e. 8–10 kbar, 350–400 °C. Metamorphic and structural data allow us to conclude that these rocks belong to the same Alpujarride unit. In the Sierra de Almagro, tectonic units with carpholite-bearing rocks overlie low-pressure, low-temperature Alpujarride units, then forming a stack with an inverted tectono-metamorphic sequence, as observed in the central and western part of the Alpujarride complex. The preservation of carpholite-bearing assemblages in these rocks implies that no significant temperature increase occurred during the exhumation history. To cite this article: G. Booth-Rea et al., C. R. Geoscience 334 (2002) 857–865.