排序方式： 共有50条查询结果，搜索用时 15 毫秒
11.
Combined morphological and thermal analysis of lava flows: A way to boost understanding of emplacement dynamics 
下载免费PDF全文
下载免费PDF全文 During emplacement, lavas modify the pre‐existing topography and release a large amount of heat. In spite of the relevance of both heat and mass release, combined morphological and thermal analyses have been seldom carried out at a flow‐field scale. Here, we consider a channelised lava flow unit formed at Mt Etna during the 2001 flank eruption, and we show that, by combining a morphological analysis of the pre‐ and post‐emplacement topography with the analysis of the syn‐eruptive thermal signature, critical insights about the processes driving mass and heat dissipation can be derived. Our results suggest that, in the considered lava flow, the pre‐emplacement slope controls heat dissipation and can influence the thickness of the final lava deposit, with possible implications for hazard assessment. The width of the lava channel, instead, appears less sensitive to the pre‐emplacement slope, and tends to regularly increase with increasing distance from the vent. 相似文献
12.
We present thermal measurements made by high spatial resolution ground-based (a hand-held thermal camera) and low spatial
resolution space-based (MODIS) instruments for a lava flow field active during the last phase of the May–July 2003 eruption
at Piton de la Fournaise (La Réunion). Multiple oblique ground-based thermal images were merged to provide full coverage of
the flow-field. These were then corrected for path length attenuation and orthorectified, allowing the at-surface radiance
emitted by the flow-field to be estimated. Comparison with the radiance recorded by the MODIS sensors during the eruption
reveals that, for clear-sky conditions and moderate-to-low viewing angles (satellite zenith <40°), the satellite measurements
represent ∼90% of the at-surface radiance, and thus represent valuable data for quantifying volcanic thermal anomalies. Nevertheless,
extreme viewing geometries and the presence of clouds strongly affect the radiance reaching the sensor and affected data from
94% of the overpasses. Ground-based thermal data were used to investigate an empirical relationship between the radiant heat
flux and lava discharge rate during the emplacement of pahoehoe flows. While the average radiation temperature for flow surface
that were 6–24 h old ranged between 500 K and 625 K, the ratio between radiative heat flux and Time-Averaged lava Discharge
Rate (TADR) ranged between 1.5 × 108 J m−3 and 3.5 × 108 J m−3. This relationship was used to estimate TADR values from optimal MODIS data and produced results in line with those obtained
from GPS surveys (Coppola et al. 2005). Our results underscore the importance of ground-based thermal analysis for the interpretation of satellite measurements,
particularly in terms of calculating discharge rate trends. 相似文献
13.
14.
Anna Coppola Giovanni Leonelli Maria Cristina Salvatore Manuela Pelfini Carlo Baroni 《Quaternary Research》2012,77(3):344-354
Tree rings from temperature-limited environments are highly sensitive climate proxies, widely used to reconstruct past climate parameters for periods prior to the availability of instrumental data and to analyse the effect of recent global warming on tree growth. An analysis of the climatic signal in five high-elevation tree-ring width chronologies of European larch (Larix decidua Mill.) from the tops of five different glacial valleys in the Italian Central Alps revealed that they contain a strong summer-temperature signal and that tree-ring growth is especially influenced by June temperatures. However, a moving correlation function analysis revealed a recent loss of the June temperature signal in the tree-ring chronologies. This signal reduction primarily involves the two lowest-altitude chronologies. It is probable that the observed increasing importance of late-summer temperature for tree-ring growth over the past 50 yr is an effect of the lengthening growing season and of the variations in the climate/tree-ring relationship over time. All the chronologies considered, especially those at the highest altitudes, show an increasing negative influence of June precipitation on tree-ring growth. The climatic signal recorded in tree-ring chronologies from the Italian Central Alps varies over time and is also differentially influenced by climatic parameters according to site elevation. 相似文献
15.
We propose a new method based on Lie transformations for simplifying perturbed Hamiltonians in one degree of freedom. The method is most useful when the unperturbed part has solutions in non-elementary functions. A non-canonical Lie transformation is used to eliminate terms from the perturbation that are not of the same form as those in the main part. The system is thus transformed into a modified version of the principal part. In conjunction with a time transformation, the procedure synchronizes the motions of the perturbed system onto those of the unperturbed part.A specific algorithm is given for systems whose principal part consists of a kinetic energy plus an arbitrary potential which is polynomial in the coordinate; the perturbation applied to the principal part is a polynomial in the coordinate and possibly the momentum.We demonstrate the strategy by applying it in detail to a perturbed Duffing system. Our procedure allow us to avoid treating the system as a perturbed harmonic oscillator. In contrast to a canonical simplification, our method involves only polynomial manipulations in two variables. Only after the change of time do we start manipulating elliptic functions in an exhaustive discussion of the flows. 相似文献
16.
17.
Resolution effects on regional climate model simulations of seasonal precipitation over Europe 总被引：5，自引：2，他引：3
We analyze a set of nine regional climate model simulations for the period 1961–2000 performed at 25 and 50 km horizontal
grid spacing over a European domain in order to determine the effects of horizontal resolution on the simulation of precipitation.
All of the models represent the seasonal mean spatial patterns and amount of precipitation fairly well. Most models exhibit
a tendency to over-predict precipitation, resulting in a domain-average total bias for the ensemble mean of about 20% in winter
(DJF) and less than 10% in summer (JJA) at both resolutions, although this bias could be artificially enhanced by the lack
of a gauge correction in the observations. A majority of the models show increased precipitation at 25 km relative to 50 km
over the oceans and inland seas in DJF, JJA, and ANN (annual average), although the response is strongest during JJA. The
ratio of convective precipitation to total precipitation decreases over land for most models at 25 km. In addition, there
is an increase in interannual variability in many of the models at 25 km grid spacing. Comparison with gridded observations
indicates that a majority of models show improved skill in simulating both the spatial pattern and temporal evolution of precipitation
at 25 km compared to 50 km during the summer months, but not in winter or on an annual mean basis. Model skill at higher resolution
in simulating the spatial and temporal character of seasonal precipitation is found especially for Great Britain. This geographic
dependence of the increased skill suggests that observed data of sufficient density are necessary to capture fine-scale climate
signals. As climate models increase their horizontal resolution, it is thus a key priority to produce high quality fine scale
observations for model evaluation. 相似文献
18.
Does the model regional bias affect the projected regional climate change? An analysis of global model projections 总被引：2，自引：0，他引：2
An analysis is presented of the dependence of the regional temperature and precipitation change signal on systematic regional biases in global climate change projections. The CMIP3 multi-model ensemble is analyzed over 26 land regions and for the A1B greenhouse gas emission scenario. For temperature, the model regional bias has a negligible effect on the projected regional change. For precipitation, a significant correlation between change and bias is found in about 30% of the seasonal/regional cases analyzed, covering a wide range of different climate regimes. For these cases, a performance-based selection of models in producing climate change scenarios can affect the resulting change estimate, and it is noted that a minimum of four to five models is needed to obtain robust precipitation change estimates. In a number of cases, models with largely different precipitation biases can still produce changes of consistent sign. Overall, it is assessed that in the present generation of models the regional bias does not appear to be a dominant factor in determining the simulated regional change in the majority of cases. 相似文献
19.
20.
Present and future climatologies in the phase I CREMA experiment 总被引：1，自引：0，他引：1
Erika Coppola Filippo Giorgi Francesca Raffaele Ramon Fuentes-Franco Graziano Giuliani Marta LLopart-Pereira Ashu Mamgain Laura Mariotti Gulilat Tefera Diro Csaba Torma 《Climatic change》2014,125(1):23-38
We provide an overall assessment of the surface air temperature and precipitation present day (1976–2005) and future (2070–2099) ensemble climatologies in the Phase I CREMA experiment. This consists of simulations performed with different configurations (physics schemes) of the ICTP regional model RegCM4 over five CORDEX domains (Africa, Mediterranean, Central America, South America, South Asia), driven by different combinations of three global climate models (GCMs) and two greenhouse gas (GHG) representative concentration pathways (RCP8.5 and RCP4.5). The biases (1976–2005) in the driving and nested model ensembles compared to observations show a high degree of spatial variability and, when comparing GCMs and RegCM4, similar magnitudes and more similarity for precipitation than for temperature. The large scale patterns of change (2070–2099 minus 1976–2005) are broadly consistent across the GCM and RegCM4 ensembles and with previous analyses of GCM projections, indicating that the GCMs selected in the CREMA experiment are representative of the more general behavior of current GCMs. The RegCM4, however, shows a lower climate sensitivity (reduced warming) than the driving GCMs, especially when using the CLM land surface scheme. While the broad patterns of precipitation change are consistent across the GCM and RegCM4 ensembles, greater differences are found at sub-regional scales over the various domains, evidently tied to the representation of local processes. This paper serves to provide a reference view of the behavior of the CREMA ensemble, while more detailed and process-based analysis of individual domains is left to companion papers of this special issue. 相似文献