Brief description of bare essentials of surface transfer and results from simulations with the HAPEX-MOBILHY data     

A. J. Pitman  C. E. Desborough 《Global and Planetary Change》1996,13(1-4)

The Bare Essentials of Surface Transfer (BEST) land surface scheme is briefly described and the key physical parameterisations discussed. Results are then presented to illustrate how the model performs, with forcing data for HAPEX-MOBILHY, compared to a series of other schemes in the simulation of evaporation and sensible heat. The implications of the models performance, and some indications of the future development of the scheme are provided. The basic version of BEST was found to overestimate evaporation for the HAPEX-MOBILHY data, simulating 816 mm yr⁻¹ compared to a range of 550 to 816 mm yr⁻¹ for all models. A modification to the β parameterisation reduced the evaporation to 759 mm yr⁻¹ which, although an improvement, is still probably too high.  相似文献   

Oceanographic influences on seabirds and cetaceans of the eastern tropical Pacific: A review     

Lisa T. Ballance  Robert L. Pitman  Paul C. Fiedler 《Progress in Oceanography》2006,69(2-4):360

This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific, the oceanic region centered on the eastern Pacific warm pool, but also including the equatorial cold tongue and equatorial current system, and summarizes what is known about oceanographic influences on seabirds and cetaceans there. The eastern tropical Pacific supports on the order of 50 species of seabirds and 30 species of cetaceans as regular residents; these include four endemic species, the world’s largest populations for several others, three endemic sub-species, and a multi-species community that is relatively unique to this ecosystem. Three of the meso-scale physical features of the region are particularly significant to seabirds and cetaceans: the Costa Rica Dome for blue whales and short-beaked common dolphins, the Equatorial Front for planktivorous seabirds, and the countercurrent thermocline ridge for flocking seabirds that associate with mixed-species schools of spotted and spinner dolphins and yellowfin tuna. A few qualitative studies of meso- to macro-scale distribution patterns have indicated that some seabirds and cetaceans have species-specific preferences for surface currents. More common are associations with distinct water masses; these relationships have been quantified for a number of species using several different analytical methods. The mechanisms underlying tropical species–habitat relationships are not well understood, in contrast to a number of higher-latitude systems. This may be due to the fact that physical variables have been used as proxies for prey abundance and distribution in species–habitat research in the eastern tropical Pacific.Though seasonal and interannual patterns tend to be complex, species–habitat relationships appear to remain relatively stable over time, and distribution patterns co-vary with patterns of preferred habitat for a number of species. The interactions between seasonal and interannual variation in oceanographic conditions with seasonal patterns in the biology of seabirds and cetaceans may account for some of the complexity in species–habitat relationship patterns.Little work has been done to investigate effects of El Niño-Southern Oscillation cycles on cetaceans, and results of the few studies focusing on oceanic seabirds are complex and not easy to interpret. Although much has been made of the detrimental effects of El Niño events on apex predators, more research is needed to understand the magnitude, and even direction, of these effects on seabirds and cetaceans in space and time.  相似文献   

A simple parameterization of sub-grid scale open water for climate models     

AJ Pitman 《Climate Dynamics》1991,6(2):99-112

The effects of small fractions ( < 30%) of open water covering a grid element are currently neglected even in atmospheric general circulation models (AGCMs) which incorporate complex land surface parameterization schemes. Here, a method for simulating sub-grid scale open water is proposed which permits any existing land surface model to be modified to account for open water. This new parameterization is tested as an addition to an advanced land surface scheme and, as expected, is shown to produce general increases in the surface latent heat flux at the expense of the surface sensible heat flux. Small changes in temperature are associated with this change in the partitioning of available energy which is driven by an increase in the wetness of the grid element. The sensitivity of the land surface to increasing amounts of open water is dependent upon the type of vegetation represented. Dense vegetation (with a high leaf area index) is shown to complicate the apparently simple model sensitivity and indicates that more advanced methods of incorporating open water into AGCMs need to be considered and compared against the parameterization suggested here. However, the sensitivity of one land surface model to incorporating open water is large enough to warrant consideration of its incorporation into climate models.  相似文献   

Thermal diffusivity of upper chalk from Hampshire,England     

John I. Pitman 《Engineering Geology》1984,20(3):207-218

The thermal diffusivity of Upper Chalk from the Micraster coranguinum zone had been calculated from 8 year temperature data obtained from depths between 30 cm and 21.34 m at Harestock, near Winchester, Hampshire.Amplitudes and phase lags were calculated from these data using Fourier analysis.Values of thermal diffusivity were calculated from the variation of amplitude with depth and phase lag with depth for the first harmonic using the Fourier heat flow equation.Agreement between the two methods was very good between 30 cm and 914 cm depth. An overall mean value is 0.004489 ± 0.00052cm^?2s^?1.Using appropriate values of porosity (47%) and density the mean thermal conductivity is 1.519W m^?1°C^?1± 0.326, for the water saturated state.  相似文献   

The contribution of the land surface energy balance complexity to differences in means, variances and extremes using the AMIP-II methodology     

N. Bagnoud  A. J. Pitman  B. J. McAvaney  N. J. Holbrook 《Climate Dynamics》2005,25(2-3):171-188

This paper explores the relationship between the complexity of the land surface energy balance parameterization and the simulation of means, variances and extremes in a climate model. We used the BMRC climate model combined with the protocol of AMIP-II to perform six ensemble simulations for each of four levels of surface energy balance complexity. Our results were then compared with other AMIP-II results in terms of the mean, variance and extremes of temperatures and precipitation. In terms of the zonally-averaged mean and the maximum temperatures and precipitation, the surface energy balance complexity did not systematically affect the BMRC climate model results. The zonal minimum temperature was affected by the inclusion of tiling and/or a temporally variable canopy conductance. We found no evidence that surface energy balance complexity affected the globally- or zonally-averaged variances. Some quite large differences were identified in the probability density functions of maximum (10 K) and minimum (4 K) temperature caused by surface tiling and/or the inclusion of a time-varying canopy conductance. With these included, the model simulated a higher probability of cooler minima and warmer maxima and therefore a different diurnal temperature range. Adding interception of precipitation led to an increase in the likelihood of more extreme precipitation. Thus, provided interception, surface tiling and a time-variable stomatal conductance are included in a land surface model, the impact of other uncertainties in the parameterization of the surface energy balance are unlikely to limit the use of climate models for simulating changes in the extremes. Most published results indicating changes to precipitation and temperature extremes due to increasing carbon dioxide are therefore unlikely to be significantly limited by uncertainty in how to parameterize the surface energy balance. Given that the variations in surface energy balance complexity included in our experiments approximates the range included in the AMIP-II models, we conclude that it this is unlikely to explain the differences found between the AMIP-II simulations. This does not mean that AMIP-II differences are not caused to a significant degree by differences in their respective LSMs, rather it limits the potential role of the land surface to non-surface energy balance components, or components (such as carbon) that are not considered here.  相似文献   

The Relative Impact of Regional Scale Land Cover Change and Increasing CO2 over China   总被引：2，自引：0，他引：2  

Mei ZHAO  Andrew J. PITMAN 《大气科学进展》2005,22(1):58-68

A series of 17-yr equilibrium simulations using the NCAR CCM3 (T42 resolution) were performed to investigate the regional scale impacts of land cover change and increasing CO2 over China. Simulations with natural and current land cover at CO2 levels of 280,355, 430, and 505 ppmv were conducted. Results show statistically significant changes in major climate fields (e.g. temperature and surface wind speed) on a 15-yr average following land cover change. We also found increases in the maximum temperature and in the diurnal temperature range due to land cover change. Increases in CO2 affect both the maximum and minimum temperature so that changes in the diurnal range are small. Both land cover change and CO2 change also impact the frequency distribution of precipitation with increasing CO2 tending to lead to more intense precipitation and land cover change leading to less intense precipitation-indeed, the impact of land cover change typically had the opposite effect versus the impacts of CO2. Our results provide support for the inclusion of future land cover change scenarios in long-term transitory climate inodelling experiments of the 21st Century. Our results also support the inclusion of land surface models that can represent future land cover changes resulting from an ecological response to natural climate variability or increasing CO2. Overall, we show that land cover change can have a significant impact on the regional scale climate of China, and that regionally, this impact is of a similar magnitude to increases in CO2 of up to about 430 ppmv. This means that that the impact of land cover change must be accounted for in detection and attribution studies over China.  相似文献   

Disk-integrated bolometric Bond albedos and rotational light curves of saturnian satellites from Cassini Visual and Infrared Mapping Spectrometer     

Karly M. Pitman  Bonnie J. Buratti 《Icarus》2010,206(2):537-560

We present values from the Cassini Visual and Infrared Mapping Spectrometer (VIMS) of four fundamental disk-integrated spectrophotometric properties (bolometric Bond albedo, solar phase curve, phase integral, and geometric albedo at 7-15 different wavelengths in the λ = 0.35-5.1 μm range) for five mid-sized saturnian icy satellites: Rhea, Dione, Tethys, Mimas, and Enceladus. These values, which include data from the period 2004-2008 and add to past VIMS phase curves, include opposition surge effects at down to fractions of a degree in solar phase angle for several moons and extend to over double the solar phase angle coverage of the Voyager mission. We also present new rotational light curves for Rhea and Dione at 7 near-infrared bands not previously available in ground-based or spacecraft studies. The bolometric Bond albedos we derive are as follows: 0.48 ± 0.09 (Rhea), 0.52 ± 0.08 (Dione), 0.61 ± 0.09 (Tethys), 0.67 ± 0.10 (Mimas), and 0.85 ± 0.11 (Enceladus). We also provide breakdowns of the major photometric quantities in both leading and trailing hemispheres. These refined parameters can be used to construct future bolometric Bond albedo maps that will contribute to surface composition identification studies, as well as models of volatile transport and sublimation. Through such applications, these data will help to determine the physical properties of surface particles, how the E-ring affects the inner saturnian moons, what is responsible for the dark albedo patterns seen on Tethys, and if these moons (e.g., Dione) are geologically active.  相似文献   

Spectroscopy, morphometry, and photoclinometry of Titan's dunefields from Cassini/VIMS     

Jason W. Barnes  Robert H. Brown  Christophe Sotin  Sebastien Rodriguez  Ross A. Beyer  Karly Pitman  Roger Clark 《Icarus》2008,195(1):400-414

Fine-resolution (500 m/pixel) Cassini Visual and Infrared Mapping Spectrometer (VIMS) T20 observations of Titan resolve that moon's sand dunes. The spectral variability in some dune regions shows that there are sand-free interdune areas, wherein VIMS spectra reveal the exposed dune substrate. The interdunes from T20 are, variously, materials that correspond to the equatorial bright, 5-μm-bright, and dark blue spectral units. Our observations show that an enigmatic “dark red” spectral unit seen in T5 in fact represents a macroscopic mixture with 5-μm-bright material and dunes as its spectral endmembers. Looking more broadly, similar mixtures of varying amounts of dune and interdune units of varying composition can explain the spectral and albedo variability within the dark brown dune global spectral unit that is associated with dunes. The presence of interdunes indicates that Titan's dunefields are both mature and recently active. The spectrum of the dune endmember reveals the sand to be composed of less water ice than the rest of Titan; various organics are consistent with the dunes' measured reflectivity. We measure a mean dune spacing of 2.1 km, and find that the dunes are oriented on the average in an east-west direction, but angling up to 10° from parallel to the equator in specific cases. Where no interdunes are present, we determine the height of one set of dunes photoclinometrically to be between 30 and 70 m. These results pave the way for future exploration and interpretation of Titan's sand dunes.  相似文献   

Storm response of a mixed sand gravel beach ridge plain under falling relative sea levels: A stratigraphic investigation using ground penetrating radar     

Sebastian J. Pitman  Harry M. Jol  James Shulmeister  Deirdre E. Hart 《地球表面变化过程与地形》2019,44(8):1610-1617

Beach ridge stratigraphy can provide an important record of both sustained coastal progradation and responses to events such as extreme storms, as well as evidence of earthquake induced sediment pulses. This study is a stratigraphic investigation of the late Holocene mixed sand gravel (MSG) beach ridge plain on the Canterbury coast, New Zealand. The subsurface was imaged along a 370 m shore-normal transect using 100 and 200 MHz ground penetrating radar (GPR) antennae, and cored to sample sediment textures. Results show that, seaward of a back-barrier lagoon, the Pegasus Bay beach ridge plain prograded almost uniformly, under conditions of relatively stable sea level. Nearshore sediment supply appears to have created a sustained sediment surplus, perhaps as a result of post-seismic sediment pulses, resulting in a flat, morphologically featureless beach ridge plain. Evidence of a high magnitude storm provides an exception, with an estimated event return period in excess of 100 years. Evidence from the GPR sequence combined with modern process observations from MSG beaches indicates that a palaeo-storm initially created a washover fan into the back-barrier lagoon, with a large amount of sediment simultaneously moved off the beach face into the nearshore. This erosion event resulted in a topographic depression still evident today. In the subsequent recovery period, sediment was reworked by swash onto the beach as a sequence of berm deposit laminations, creating an elevated beach ridge that also has a modern-day topographic signature. As sediment supply returned to normal, and under conditions of falling sea level, a beach ridge progradation sequence accumulated seaward of the storm feature out to the modern-day beach as a large flat, uniform progradation plain. This study highlights the importance of extreme storm events and earthquake pulses on MSG coastlines in triggering high volume beach ridge formation during the subsequent recovery period. © 2019 John Wiley & Sons, Ltd.  相似文献   

1D PetroMod software modeling of the Basrah oil fields, Southern Iraq     

Thamer K. Al-Ameri  Mohamed S. A. Jafar  Janet Pitman 《Arabian Journal of Geosciences》2013,6(10):3783-3808

1D (Petromod) hydrocarbon charge modeling and source rock characterization of the Lower Cretaceous and Upper Jurassic underlying the prolific Cretaceous and Tertiary reservoirs in the Basra oilfields in southern Iraq. The study is based on well data of the Majnoon, West Qurna, Nahr Umr, Zubair, and Rumaila oil fields. Burial histories indicate complete maturation of Upper Jurassic source rocks during the Late Cretaceous to Paleogene followed by very recent (Neogene) maturation of the Low/Mid Cretaceous succession from early to mid-oil window conditions, consistent with the regional Iraq study of Pitman et al. (Geo Arab 9(4):41–72, 2004). These two main phases of hydrocarbon generation are synchronous with the main tectonic events and trap formation associated with Late Cretaceous closure of the neo-Tethys; the onset of continent–continent collision associated with the Zagros orogeny and Neogene opening of the Gulf of Suez/Red Sea. Palynofacies of the Lower Cretaceous Sulaiy and Lower Yamama Formations and of the Upper Jurassic Najmah/Naokelekan confirm their source rock potential, supported by pyrolysis data. To what extent the Upper Jurassic source rocks contributed to charge of the overlying Cretaceous reservoirs remains uncertain because of the Upper Jurassic Gotnia evaporite seal in between. The younger Cretaceous rocks do not contain source rocks nor were they buried deep enough for significant hydrocarbon generation.  相似文献