A case study of cirrus layers with variable 3.74 µm reflection properties in the first FIRE experiment, 2 November 1986     

C. M. R. Platt  A. Arking 《Theoretical and Applied Climatology》1997,56(3-4):137-152

Summary Remotely sensed scanning radiometer and lidar data on cirrus clouds were obtained during the cirrus FIRE IFO experiment in November 1986 from the ER-2 aircraft plat-form.Data were examined particularly on 2 November for an area in the vicinity of Wausau, Wisconsin where unusual effects were noticed in bispectral histograms from various channels in the scanner data.After calibration of the data in spectral channels of both the Scan Cloud Radiometer (SCR) and Multichannel Cloud Radiometer (MCR) instruments, including direct comparison between compatible channels in the two instruments, it was found that the 0.856 µm SCR channel gave good data, whereas the 0.665 µm and 0.74 µm SCR channels gave large offsets, when compared with the MCR 0.754 µm data. The latter channel was found to compare well in a second comparison with coincident AVHRR channel satellite data. Similarly, the SCR 11.17 µm data gave consistent results and the SCR 3.74 µm data were carefully calibrated.Bispectral histograms formed between 0.856 µm, 3.74 µm and 11.17 µm SCR channel data indicated that some coherent layers of cirrus clouds were giving enhanced solar reflectance at 3.74 µm, indicative of small (~ <25 µm radius) particles, whereas other neighbouring layers gave little reflectance.A comparison of 0.856 µm reflections with 11.17 µm absorption optical depth indicated that the small particles where probably ice crystals. A comparison of 3.74 µm solar albedo and 11.17 µm absorption optical depths of these layers with theoretical calculations for ice spheres indicated a mode radius of about 8 µm for the cloud particle size distribution. An estimate from similar recent calculations on hexagonal ice crystals indicated that the retrieved effective radius would be increased to 25 µm. The difference between the two retrieved radii was a measure of the uncertainty in the retrievals, considering also differences in the assumed size distributions.Qualitative comparison with ER-2 lidar data gave a tentative identification of the reflecting layers.The results demonstrate the power of the 3.74 µm channel for identification of small-particle layers in cirrus.With 9 Figures  相似文献   

Biological oceanography and fisheries management: perspective after 10 years   总被引：1，自引：0，他引：1  

Platt  Trevor; Sathyendranath  Shubha; Fuentes-Yaco  Cesar 《ICES Journal of Marine Science》2007,64(5):863-869

  相似文献   

Picoplankton: Contribution to Phytoplankton Production in the Strait of Messina*     

Giuseppe Magazz  Vivia Bruni  Augusto Piccione  Trevor Platt  Brian Irwin  D. V. Subba Rao 《Marine Ecology》1987,8(1):21-31

Abstract. Biomass and primary production rates derived from photosynthesis-light curves on picoplankton (< 1 um fraction) and total phytoplankton were compared for the Strait of Messina. Picoplankton biomass ranged between 0.063 and 0.094 mg Chi a m^-5 and accounted for 56–63 % of the total. Total primary production rates were between 0.22 and 1.56 mg C-m^-2-h^-1 of which the picoplankton contribution ranged from 24 to 43%. In this turbulent nearshore environment, the contribution of picoplankton to total phytoplankton production is considerably less than in calmer open-ocean waters. Carbon assimilation numbers (Pm^b), the initial slope (a), adaptation parameter (I_k), optimal irradiance (I_m) and compensation intensity (L_m,) for the picoplankton were lower than for the > 1 μm fraction. Fitted respiration (Rm^B) for the picoplankton was, however, on the average higher (10.3 % of Pm^B) than for the > 1 μrn fraction (6.6 %). Assimilation numbers for the > 1 μm fraction in the southern stations were of higher magnitude (8.5–12.0 mg C mg Chi a^-1 h^-1) than in the northern station, possibly due to the impact of upwelled water flowing southward along the Sicilian coast.  相似文献   

IDOAS: A new monitoring technique to study the 2D distribution of volcanic gas emissions   总被引：1，自引：0，他引：1  

N. Bobrowski  G. Hnninger  F. Lohberger  U. Platt 《Journal of Volcanology and Geothermal Research》2006,150(4):329-338

Imaging Differential Optical Absorption Spectroscopy (IDOAS) is an optical remote-sensing method using scattered sunlight as light source. It combines a “pushbroom” imaging spectrometer with the DOAS technique and thus allows imaging two-dimensional trace gas distributions, e.g., in volcanic plumes. The highly sensitive and specific detection of many trace gases simultaneously (specific molecules, not just elements, e.g. SO₂, BrO, NO₂, O₃, HCHO, etc.) is possible, and the temporal and spatial variation of these gases can be measured. The IDOAS system presented here enables the taking of two-dimensional images of trace gas distributions in a volcanic plume with a spatial resolution of 100 pixels horizontally × 64 pixels vertically, each with a field of view of 0.087° in horizontal and 0.208° in vertical directions. Therefore, IDOAS provides useful information about the chemical composition and chemical variability in a volcanic plume and allows studying plume dispersal and chemical transformations. The technique was applied to map the SO₂ distribution in the plume of Mt. Etna volcano for the first time in October 2003.  相似文献   

Internal structure of a collapsed terrain: The Lújar syncline and its significance for the fold- and sheet-structure of the Alborán Domain (Betic Cordilleras, Spain)     

Miguel Orozco  Antonio M lvarez-Valero  Francisco M Alonso-Chaves  John P Platt 《Tectonophysics》2004,385(1-4):85-104

Detailed structural analysis of the Sierra de Lújar in the western Alpujarras region (Betic Cordilleras, S Spain), a very representative area of the terrain known as the Alborán Domain, has revealed the existence of a very large N-vergent recumbent syncline which involves the whole mountain massif and neighbouring areas. The Lújar syncline and, probably, the associated recumbent anticline which crops out southeast of Sierra de Lújar show a great variation in the orientation of the hinge line. Although having a curved shape, the hinge line is contained in a plane whose attitude coincides with the main attitude of the axial-plane crenulation foliation (Sc), suggesting that it is a sheath fold.The strongly deformed overturned limb of the syncline is cut by two low-angle normal faults displacing towards the north. Similarity in the kinematics between the faults and the fold, and the association between the faults and the high-strain zone in the overturned limb of the fold, suggest that they are related. Regional constraints on the age of the crenulation cleavage and the low-angle normal faults indicate that they formed during the early Miocene late-orogenic extensional event in the Alborán Domain.We propose an alternate explanation for the structure of the Alpujarras region in which the Lújar syncline forms part of a recumbent syncline–anticline pair that extends along much of the Alpujarride outcrop in the southern Betic Cordillera. In several places, the fold is disrupted by low-angle normal faults, and it is overlain by an upper Alpujárride extensional sheet mainly composed of medium- to high-grade metamorphic rocks. We suggest that all these structures arose from the extensional deformation under decreasing temperature conditions of a previously thickened and metamorphosed orogenic crust.  相似文献   

The History of Recent Limnological Changes and Human Impact on Upper Klamath Lake, Oregon     

J. Platt Bradbury  Steven M. Colman  Richard L. Reynolds 《Journal of Paleolimnology》2004,31(2):151-165

Hypereutrophic Upper Klamath Lake has been studied for almost 50 years to evaluate the nature, cause, and effects of its very productive waters. Mitigation of undesirable effects of massive cyanobacterial blooms requires understanding their modern causes as well as their history. Knowledge of the pre-settlement natural limnology of this system can provide guidelines for lake restoration and management of land and water use strategies to maximize the benefits of this aquatic resource. This investigation uses a paleolimnological approach to document the nature and chronology of limnological and biological changes in Upper Klamath Lake for the past 200 years, covering the time when the lake was first described until today. A 45-cm gravity core, dated by ²¹⁰Pb and diatom correlations, was analyzed for diatoms, pollen, akinetes (resting spores) of the cyanobacterium Aphanizomenon flos-aquae, reworked tephra shards, and sediment magnetic characteristics. Pollen profiles show little vegetation change during this time. In contrast, diatoms indicative of increased nutrient fluxes (P and Si) increase moderately, coinciding with the settlement of the region by Euro-Americans. Numerous settlement activities, including draining of lake-margin marshes, upstream agriculture and timber harvest, road construction, and boat traffic, may have affected the lake. Magnetic properties and reworked tephra suggest riparian changes throughout the basin and increased lithogenic sediment delivery to the lake, especially after 1920 when the marshes near the mouth of the Williamson River were drained and converted to agricultural and pasture land. Drainage and channelization also decreased the ability of the marshes to function as traps and filters for upstream water and sediments. Akinetes of Aphanizomenon flos-aquae record progressive eutrophication of Upper Klamath Lake beginning in the 20th century and particularly after 1920 when lake-margin marsh reclamation more than doubled. The coincidence of limnological changes and human activities following European settlement suggests a major impact on the Upper Klamath Lake ecosystem, although ascribing specific limnological changes to specific human activities is difficult.  相似文献   

Free Radicals and Fast Photochemistry during BERLIOZ   总被引：4，自引：0，他引：4  

U. Platt  B. Alicke  R. Dubois  A. Geyer  A. Hofzumahaus  F. Holland  M. Martinez  D. Mihelcic  T. Klüpfel  B. Lohrmann  W. Pätz  D. Perner  F. Rohrer  J. Schäfer  J. Stutz 《Journal of Atmospheric Chemistry》2002,42(1):359-394

The free radicals OH, HO₂, RO₂, and NO₃ are known to be the driving force for most chemical processes in the atmosphere. Since the low concentration of the above radicals makes measurements particularly difficult, only relatively few direct measurements of free radical concentrations have been reported to date.We present a comprehensive set of simultaneous radical measurements performed by Laser Induced Fluorescence (LIF), Matrix Isolation –Electron spin Resonance (MI-ESR), Peroxy Radical Chemical Amplification (PERCA), and Differential Optical Absorption Spectroscopy (DOAS) during the BERLIner OZonexperiment (BERLIOZ) during July and August of 1998 near Berlin, Germany. Most of the above radical species were measured by more than one technique and an intercomparison gave good agreement. This data set offered the possibility to study and quantify the role of each radical at a rural, semi-polluted site in the continental boundary layer and to investigate interconnections and dependencies among these free radicals.In general (box) modelled diurnal profiles of the different radicals reproduced the measurements quite well, however measured absolute levels are frequently lower than model predictions. These discrepancies point to disturbing deficiencies in our understanding of the chemical system in urban air masses.In addition considerable night-time peroxy radical production related to VOC reactions with NO₃ and O₃ could be quantified.  相似文献   

Nepheline-bearing rocks from the Poohbah Lake complex,Ontario: Malignites and Malignites     

Roger H. Mitchell  R. Garth Platt 《Contributions to Mineralogy and Petrology》1979,69(3):255-264

Malignites from the Poohbah Lake complex of northwestern Ontario, Canada are melanocratic cumulates. Cumulus pyroxene and apatite are poikilitically enclosed in a groundmass of large plates of intercumulus orthoclase and nepheline. Nepheline-feldspar fingerprint-like intergrowths occur. Nephelines are commonly zeolitized and pyroxenes altered to aggregates of biotite and/or garnet by deuteric alteration. Pyroxenes are weakly zoned from Di₇₁ Hd¹⁸Ac₁₁ to Di₆₃Hd₂₂Ac₁₅, and are similar to the least evolved pyroxenes of other alkaline rocks. Nephelines all have compositions within the Morozewicz-Buerger convergence field and feldspars have a limited compositional range from Or⁸⁸ to Or⁹⁵. Perthites are absent.Inconsistancies in the usage of the terms malignite and juvite are discussed and it is considered that a non-genetic petrographic classification of nepheline syenites leads to the obscuration of a group of potassic nepheline syenites, characterized by the presence of nepheline plus orthoclase which are typically associated with saturated to over-saturated alkaline rocks, contain pseudo-leucite or nepheline-orthoclase intergrowths, are emplaced in mobile belts and are not associated with rocks of the ijolite-carbonatite suite.A genetic classification of nepheline syenites is suggested and it is proposed that; (1) mafic-rich nepheline syenites be referred to as mela-nepheline syenites (sensu lato) rather than as malignites; (2) the term malignite be used for magmatic potassic nepheline syenites characterised by the presence of nepheline plus a single potassium-rich feldspar (orthoclase or microcline) and devoid of exsolution perthite under subsolvus conditions; (3) the metasomatic malignites and juvites of ijolite-carbonatite complexes be referred to as varieties of fenites.  相似文献   

Crustal development in the Agnew region,Western Australia,as shown by Rb/Sr isotopic and geochemical studies     

J.A Cooper  R.W Nesbitt  J.P Platt  G.E Mortimer 《Precambrian Research》1978,7(1):31-59

Rb/Sr geochronology on a folded greenstone-granitoid complex in the Agnew area, Western Australia, yields four distinct ages of igneous activity that conform with stratigraphic and intrusive relationships. They are (using $\text{λ}{}^{87}\text{Rb}\text{= 1.42 · 10}{}^{\mathrm{?11}}\text{a}{}^{\mathrm{?1}}$, NBS 70A = 522 ppm Rb and 65.3 ppm Sr):