Based on a series of experiments conducted by two regional climate models (RCA4 and LMDZ) with and without soil moisture-atmosphere coupling, we investigate the role of soil moisture on the occurrence of surface air temperature extremes and its persistence in Southeastern South America. Our analysis reveals that both factors, soil moisture-atmosphere coupling and relatively drier soil conditions, enhance the temperature extremes. In addition, the existence of soil-atmosphere coupling and the associated soil moisture variability is crucial for the development of the extremes in SESA. The key role of soil-atmosphere coupling is also reflected in the intrinsic persistence of hot days, which is greater in simulations with interactive soil moisture than in those with prescribed soil conditions. In the absence of soil-atmosphere coupling, the imprint of the anomalous dry (and also wet) soil conditions on the intensity and persistence of hot days is weaker.
The coupled climate model EC-Earth2 is used to investigate the impact of direct radiative effects of aerosols on stationary waves in the northern hemisphere wintertime circulation. The direct effect of aerosols is simulated by introducing prescribed mixing ratios of different aerosol compounds representing pre-industrial and present-day conditions, no indirect effects are included. In the EC-Earth2 results, the surface temperature response is uncorrelated with the highly asymmetric aerosol radiative forcing pattern. Instead, the anomalous extratropical temperature field bears a strong resemblance to the aerosol-induced changes in the stationary-wave pattern. It is demonstrated that the main features of the wave pattern of EC-Earth2 can be replicated by a linear, baroclinic model forced with latent heat changes corresponding to the anomalous convective precipitation generated by EC-Earth2. The tropical latent heat release is an effective means of generating stationary wave trains that propagate into the extratropics. Hence, the results of the present study indicate that aerosol-induced convective precipitation anomalies govern the extratropical wave-field changes, and that the far-field temperature response dominates over local effects of aerosol radiative forcing. 相似文献
Quasi-thermal noise (QTN) spectroscopy is one of the most effective tools for in situ diagnostics in space plasmas (Meyer-Vernet et al., 1998; Meyer-Vernet and Perche, 1989; Chugunov and Trakhtengerts, 1978). This method produces routine measurements of the
bulk electron density and temperature; recently it has been extended to measure the ion bulk speed. Among the advantages of
the method its immunity to spacecraft potential and photoelectron perturbations should be noted. Quasi-thermal noise spectroscopy
is used particularly on Ulysses and Wind. However for the interpretation of QTN data the calculation of the noise voltage
induced on antennas under different conditions is necessary. This question is especially complicated and so far insufficiently
studied in magnetized plasmas. In the present paper we calculate the spectrum of the noise voltage induced on a dipole antenna
in the upper hybrid frequency range. The computations are adapted to the interpretation of data acquired on the Ulysses and
Wind spacecraft.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
We have started a survey of galaxies at intermediate redshifts using the HST-STIS parallel fields. Our main goal is to analyse
the morphology of faint galaxies in order to estimate the epoch of formation of the Hubble classification sequence. The high
resolution of STIS images (0.05″) is ideal for this work and enables us to perform a morphological classification and to analyse
the internal structures of galaxies. We find that 40% of the 290 galaxies are early types and that there are more irregulars
and ellipticals at the fainter magnitudes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
Non-columnar stromatolites occur in the late Precambrian Annijokka Member of the Båtsfjord Formation of the Varanger peninsula, north Norway. The stromatolites form biostromes up to 0.5 m thick embedded within peritidal, shallowing-up, siliciclastic-dolomite cycles. The stromatolite biostromes tend to occur in the upper, dolomite-rich portions of the cycles and are mostly calcite-dominated.Interpretation of the origin of the host sediments, combined with the location of the biostromes in the depositional sequences and with the contrasting mineralogy between the latter and the stromatolites, suggests that the majority of the stromatolite biostromes originated in freshwater and schizohaline supralittoral ponds. 相似文献
Abstract— In January 2006, the Stardust mission will return the first samples from a solid solar system body beyond the Moon and the first samples of contemporary interstellar dust ever collected. Although sophisticated laboratory instruments exist for the analysis of Stardust samples, techniques for the recovery of particles and particle residues from aerogel collectors remain primitive. Here, we describe our recent progress in developing techniques for extracting small volumes of aerogel, which we have called “keystones,” which completely contain particle impacts but minimize the damage to the surrounding aerogel collector. These keystones can be fixed to custom‐designed micromachined silicon fixtures (so called “microforklifts”). In this configuration, the samples are self‐supporting, which can be advantageous in situations where interference from a supporting substrate is undesirable. The keystones may also be extracted and placed onto a substrate without a fixture. We have also demonstrated the capability of homologously crushing these unmounted keystones for analysis techniques that demand flat samples. 相似文献
Abstract— Powdered Allende projectiles were fired into silica aerogel at 6.1 km/sec in order to evaluate particle retrieval and analysis techniques for samples from the Stardust mission. Since particles may disintegrate and ablate along the penetration paths in a high‐porosity aerogel, TOF‐SIMS analysis may be a suitable method to determine the distribution of such materials along the tracks as well as potential compositional modifications. Therefore, two ?350 μm‐sized tracks, residing at the surface of a keystone specimen that was flattened between two silicon chips, were analyzed. TOF‐SIMS allows for a detailed study of the chemical composition of particles that survived the impact mostly intact and of fine‐grained material from disintegrated projectiles. In the investigated keystone, material from light gas gun debris dominated. Besides the two tracks, a continuous, 40‐μm‐thick surface layer of implanted material—probably gun residue—was found. One of the two analyzed tracks is compositionally distinct from this surface layer and is likely to contain residual material of an Allende projectile. The analyses clearly demonstrate that tracks, resulting from impactors in the 5–10 μm size range, can be successfully analyzed with TOF‐SIMS. 相似文献
The peculiar ring galaxies are formed as a result of a cosmic interaction. An intruder galaxy plunges through the center of
a rotating disk galaxy triggering radially expanding density waves inside the disk. In this paper we exploited SPH simulations
with the aim to examine the role of a “live” halo and/or bulge in driving the morphology of the interacting galaxy. Moreover
we explore the effects of different implementations of the shear viscosity and of the pressure gradient in the code. 相似文献