INDEX surface temperature

Myneni, R. B., Los, S. O. and Tucker, C. J. (1996). Satellite-based identification of linked vegetation index and sea surface temperature anomaly areas from 1982-1990 for Africa, Australia and South America, Geophys. Res. Lett. 23, 729-732. 

The existence of active sites on surfaces has long been postulated, but confidence in the geometric models of kink and step sites has only been attained in recent years by work on high index surfaces. However, even a lattice structure that is unreconstructed will show a number of random defects, such as vacancies and isolated adatoms, purely as a result of statistical considerations. What has been revealed by the modern techniques described in chapter 2 is the extraordinary mobility of surfaces, particularly at the liquid-solid interface. If the metal atoms can be stabilised by coordination, very remarkable atom mobilities across the terraces are found, with reconstruction on Au(100), for example, taking only minutes to complete at room temperature in chloride-containing electrolytes. It is now clear that the... 

The discussion on the experimental evidence for the existence of roughening on low indexed surfaces is not yet settled. Let us consider for example the Cu(110) surface. More than ten years ago it had been noticed that the intensities in the photoemission spectra taken from Cu(l 10) decrease rapidly with temperature above 500 K Similar effects have been seen recently in... 

Figure 14.54, for example, shows the annual average number of sunspots from 1880 to the present, which clearly shows this cycle (Cliver et al., 1998). Both the sunspot number and the aa geomagnetic index have been used as proxies for the solar cycle. For the relatively short time period covered by available instrumental temperature records, both the sunspot number and the aa geomagnetic index are correlated to surface temperature (e.g., see Cliver et al., 1998 and Wilson, 1998). 

Cliver, E. W., V. Boriakoff, and J. Feynman, Solar Variability and Climate Change Geomagnetic aa Index and Global Surface Temperature, Geophys. Res. Lett., 25, 1035-1038 (1998). 

Fig. 5. Global average surface temperature trend 1850-2000. Scale on y-axis (°C) is indexed to 1970 global average surface temperature. (Adapted from Carbon Dioxide Information Analysis Center 2000.)...

One of the most exciting observations of LEED studies of adsorbed monolayers on low Miller index crystal surfaces is the predominance of ordering within these layers (18). These studies have detected a large number of surface structures formed upon adsorption of different atoms and molecules on a variety of solid surfaces. Conditions range from low temperature, inert gas physisorption to the chemisorption of reactive diatomic gas molecules and hydrocarbons at room temperature and above. A listing of over 200 adsorbed surface structures, mostly of small molecules, adsorbed on low Miller index surfaces can be found in a recent review (/). 

The chemisorption of over 25 hydrocarbons has been studied by LEED on four different stepped-crystal faces of platinum (5), the Pt(S)-[9(l 11) x (100)], Pt(S)-[6(l 11) x (100)], Pt(S)-[7(lll) x (310)], and Pt(S)-[4(l 11 x (100)] structures. These surface structures are shown in Fig. 7. The chemisorption of hydrocarbons produces carbonaceous deposits with characteristics that depend on the substrate structure, the type of hydrocarbon chemisorbed, the rate of adsorption, and the surface temperature. Thus, in contrast with the chemisorption behavior on low Miller index surfaces, breaking of C-H and C-C bonds can readily take place at stepped surfaces of platinum even at 300 K and at low adsorbate pressures (10 9-10-6 Torr). Hydrocarbons on the [9(100) x (100)] and [6(111) x (100)] crystal faces form mostly ordered, partially dehydrogenated carbonaceous deposits, while disordered carbonaceous layers are formed on the [7(111) x (310)] surface, which has a high concentration of kinks in the steps. The distinctly different chemisorption characteristics of these stepped-platinum surfaces can be explained by... 

In a series of studies, the dehydrogenation and hydrogenolysis of cyclohexane was studied on both the stepped and low Miller index (111) crystal faces of platinum at a surface temperature of 300°C and a hydrogen to cyclohexane ratio of 20 1. While the rates on the stepped and low Miller index surfaces were not very different for the formation of benzene and hexane, the formation of cyclohexene was very structure sensitive, its rate being 100 times greater on the stepped surface than on the (111) crystal face. In Table III mrnnare the initial turnover numbers for the various reactions at low... 

Defects lead to a roughening of crystal surfaces with increasing temperature as already predicted by Burton et al. [335], However, calculations for low-index surfaces yield roughening transition temperatures well above the melting temperature. The reason is the high forma-... 

These changes may be related to the two warm winters that occurred in 1998 and 1999, which could affect the balance between input of freshwater from the rivers and saline water from the Bosporus and the winter formation of the oxygen-rich CIL. These years are remarkable for the increase of the Sea surface temperature (Fig. 8), increase of temperature in the core of the CIL [82,85-87], and shoaling of the CIL in the density field [48]. All these events can be connected with the weather condition oscillations, as follows from North Atlantic oscillation (NAO) index behavior (Fig. 8). 

In principle, the optical absorptions in this region could also be associated with point defects on the surface either with or without trapped electrons and holes. However, the properties of the charged defects have been studied extensively, and the trapped charges can be thermally annealed at temperatures far lower than the normal preparation temperatures of these samples. In addition, they are characterized by optical and EPR spectra which are not observed in these samples. Contributions from point defects with no trapped charges cannot easily be eliminated. In fact, such a surface vacancy or divacancy would represent a localized state on a low-index surface associated with 4-coordinated ions. 

As should become clear, the U37 index appears nevertheless to provide a remarkably faithful estimate of paleotemperamres near the sea surface. At the same time, difficulties in matching the space and timescales of modem process studies to the information contained in sediments mean that the caveats raised above remain significant. Field studies provide only snapshots of haptophyte abundance and alkenone unsaturation parameters, sediment traps provide only a few years of data at only a few locations in the global ocean, and it is unclear how well laboratory cultures replicate the natural environment. I have endeavored to treat different lines of evidence systematically, but I have found it difficult to discuss each aspect in a purely serial way. The reader will therefore be asked to digest a review in which very diverse measurements and paradigms are woven together to answer the central question of how to reconstmct past ocean surface temperatures with the U37 proxy. 

The success of core-top temperature calibrations indicates that physiological state, genetic variability, and depth and seasonality of production play secondary roles to the control on the sedimentary U37 index exerted by mean annual near-surface temperature. In most cases, these factors produce errors at the level of 1.5 °C or less in the global core-top calibration. To this observer s opinion, core-top data cannot be reconciled with the large variations in the U 7 index attributed to genetic or physiological factors by some culture studies. This does not indicate that the culture data are wrong in a technical sense, but that their results cannot always be extrapolated to the natural environment (Popp et al., 1998). 

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