Good Spatial Coverage Research Articles

Review on the applications of Tropospheric Emissions Spectrometer to air-quality research: Perspectives for China

The Tropospheric Emissions Spectrometer (TES) aboard the National Aeronautics and Space Administration’s (NASA’s) Aura satellite launched in July 2004 is the first satellite instrument to provide simultaneous retrievals of ozone (O3) and carbon monoxide (CO) throughout the Earth’s lower atmosphere. This paper briefly reviews the TES instrument, the retrieval of O3 and CO profiles, and the validation of the retrievals. The applications of TES O3 and CO products include mapping the vertical and horizontal distribution of tropospheric O3 and CO and their correlations, examining the regional and continental outflow, and analyzing the variability of the two species associated with certain weather and climatic conditions, such as El Nino and the Asian monsoon. TES retrievals of O3 and CO offer an important new source of satellite data over China with good spatial and temporal coverage that can provide evaluation and constraints on the performance of chemical transport models in simulating the general features of ozone pollution over China. Special observations have been conducted and requests may be submitted to the TES team to make geographically focused observations of O3 and CO over China.

Coastal and global sea level change

Both coastal and global mean sea level rise by about 3.0 ± 0.5 mm/year from January 1993 to December 2004. Over shorter intervals the coastal sea level rises faster and over longer intervals slowly than the global mean, which trend is almost constant for each interval and is equal to 2.9 ± 0.5 mm/year in 1993–2008. The different trends are due to the higher interannual variability of coastal sea level, caused by the sea level regional variability, that is further averaged out when computing the global mean. Coastal sea level rise is well represented by a selected set of 267 stations of the Permanent Service for Mean Sea Level and by the corresponding co-located altimeter points. Its departure from coastal sea level computed from satellite altimetry in a 150 km distance from coast, dominated by a large rise in the Eastern Pacific, is due to the regional interannual variability. Regionally the trends of the coastal and open-ocean sea level variability are in good agreement and the main world basins have a positive averaged trend. The interannual variability is highly correlated with the El Nino Southern Oscillation (SO) and the North Atlantic Oscillation (NAO) climatic indices over both the altimeter period and the interval 1950–2001. Being the signal of large scale a small number of stations with good spatial coverage is needed. The reconstruction of the interannual variability using the spatial pattern from altimetry and the temporal patterns from tide gauges correlated to NAO and SOI restitutes about 50% of the observed interannual variability over 1993–2001.

Evaluation of remote‐sensing‐based rainfall products through predictive capability in hydrological runoff modelling

AbstractThe emergence of regional and global satellite‐based rainfall products with high spatial and temporal resolution has opened up new large‐scale hydrological applications in data‐sparse or ungauged catchments. Particularly, distributed hydrological models can benefit from the good spatial coverage and distributed nature of satellite‐based rainfall estimates (SRFE). In this study, five SRFEs with temporal resolution of 24 h and spatial resolution between 8 and 27 km have been evaluated through their predictive capability in a distributed hydrological model of the Senegal River basin in West Africa. The main advantage of this evaluation methodology is the integration of the rainfall model input in time and space when evaluated at the sub‐catchment scale. An initial data analysis revealed significant biases in the SRFE products and large variations in rainfall amounts between SRFEs, although the spatial patterns were similar. The results showed that the Climate Prediction Center/Famine Early Warning System (CPC‐FEWS) and cold cloud duration (CCD) products, which are partly based on rain gauge data and produced specifically for the African continent, performed better in the modelling context than the global SRFEs, Climate Prediction Center MORPHing technique (CMORPH), Tropical Rainfall Measuring Mission (TRMM) and Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN). The best performing SRFE, CPC‐FEWS, produced good results with values of R2NS between 0·84 and 0·87 after bias correction and model recalibration. This was comparable to model simulations based on traditional rain gauge data. The study highlights the need for input specific calibration of hydrological models, since major differences were observed in model performances even when all SRFEs were scaled to the same mean rainfall amounts. This is mainly attributed to differences in temporal dynamics between products. Copyright © 2009 John Wiley & Sons, Ltd.

Identification and verification of ultrafine particle affinity zones in urban neighbourhoods: sample design and data pre-processing

A methodology is presented and validated through which long-term fixed site air quality measurements are used to characterise and remove temporal signals in sample-based measurements which have good spatial coverage but poor temporal resolution. The work has been carried out specifically to provide a spatial dataset of atmospheric ultrafine particle (UFP < 100 nm) data for ongoing epidemiologic cohort analysis but the method is readily transferable to wider epidemiologic investigations and research into the health effects of other pollutant species.

Accelerated focused ultrasound imaging

One of the most basic trade-offs in ultrasound imaging involves frame rate, depth, and number of lines. Achieving good spatial resolution and coverage requires a large number of lines, leading to decreases in frame rate. An even more serious imaging challenge occurs with imaging modes involving spatial compounding and 3-D/4-D imaging, which are severely limited by the slow speed of sound in tissue. The present work can overcome these traditional limitations, making ultrasound imaging many-fold faster. By emitting several beams at once, and by separating the resulting overlapped signals through spatial and temporal processing, spatial resolution and/or coverage can be increased by many-fold while leaving frame rates unaffected. The proposed approach can also be extended to imaging strategies that do not involve transmit beamforming, such as synthetic aperture imaging. Simulated and experimental results are presented where imaging speed is improved by up to 32-fold, with little impact on image quality. Object complexity has little impact on the method's performance, and data from biological systems can readily be handled. The present work may open the door to novel multiplexed and/or multidimensional protocols considered impractical today.

Characterization of methane retrievals from the IASI space-borne sounder

Abstract. Although the global methane (CH4) concentration has more than doubled since pre-industrial times, local emission sources are still poorly identified and quantified. Instruments onboard satellites can improve our knowledge about the methane global distribution owing to their very good spatial coverage. The IASI (Infrared Atmospheric Sounding Interferometer) instrument launched on the European MetOp-A platform is a Fourier transform spectrometer which measures the thermal infrared radiation emitted by the Earth and its atmosphere. In this paper, we present the first global distribution of methane total columns (mostly sensitive to the middle troposphere) from the IASI spectra using the methane ν4 absorption band. The retrieval spectral range was set in order to minimize possible spectroscopic issues. Results are discussed in terms of error budget and vertical sensitivity. In addition, we study the gain of information on surface methane concentrations provided by using the ν3 band, which is partly covered by IASI on the short-wave end of the spectra (extending to 2760 cm−1), where solar reflection contributes significantly.

Estimating rainfall erosivity from daily precipitation records: A comparison among methods using data from the Ebro Basin (NE Spain)

Summary Among the major factors controlling soil erosion, as vegetation cover or soil erodibility, rainfall erosivity has a paramount importance since it is difficult to predict and control by humans. Accurate estimation of rainfall erosivity requires continuous rainfall data; however, such data rarely demonstrate good spatial and temporal coverage. Daily weather records are now commonly available, providing good coverage that better represents rainfall intensity behavior than do more aggregated rainfall data. In the present study annual rainfall erosivity was estimated from daily rainfall records, and compared to data obtained employing the RUSLE R factor procedure. A spatially-dense precipitation database of high temporal resolution (15 min) was used. Two methodologies were applied: (i) daily rainfall erosivity estimated using several parametric models, and, (ii) annual rainfall erosivity estimated by regression-based techniques employing several intensity precipitation indices and the modified Fournier index. To determine the accuracy of estimates, several goodness-of-fit and error statistics were computed in addition to a spatial distribution comparison. The daily rainfall erosivity models accurately predicted annual rainfall erosivity. Parametric models with few combined parameters and a periodic function simulating intra-annual rainfall behavior provided the best results. Where daily rainfall records were not available, good estimates of annual rainfall erosivity were also obtained using regression-based techniques based on 5-day maximum precipitation events, the maximum wet spell duration, and the ratio between the lengths of average wet and dry spells. Inherent limitations remain in the use of daily weather records for estimating rainfall erosivity. Future research should focus on incorporating measures of natural rainfall properties of the particular region, including kinetic energy and intensity, and their effects on the soil.

The Apparent Layered Structure of the Heliospheric Current Sheet: Multi-Spacecraft Observations

Multiple current sheet crossings are ubiquitous features of the solar wind associated with high-beta plasma sheets, notably during the passage of the heliospheric current sheet (HCS). As the HCS is being convected past near-Earth, we attempt to resolve spatial scales and temporal variations of the apparent layered structure of the HCS, including adjacent large scale field reversals. We use several spacecraft for good spatial and cross-scale coverage, spanning 550 R-E across and 900 R-E along the Sun -aEuro parts per thousand Earth line: STEREO, ACE and Cluster. The multi-spacecraft magnetic and plasma observations within the leading edge of the sector boundary are consistent with i) a broad multi-layered structure; ii) occasional non-planar structures and Alfv,nic fluctuations; iii) various stages of transient outflowing loops formed by interchange reconnection. By comparison of the observations at each spacecraft, we obtain a synthesis of the evolution between the patterns of loops, and hence of the transient outflow evolution along the sector boundary. In particular, we present circumstantial evidence that a heat flux dropout, traditionally signalling disconnection, can arise from interchange reconnection and scattering. Moreover, the inter-spacecraft comparison eliminates ambiguities between interpretations of electron counterstreaming. Overall, the sector boundary layer remains, locally, a steady structure as it is convected in the solar wind across a radial heliospheric distance of 560 -aEuro parts per thousand 580 R-E. However, non-planar structures on the Cluster spatial scale, as well as the variations in angular changes and transition durations on the broader scale, indicate that we are not following the evolution of single loops but more likely a bunch of loops with variable properties.

Anthropogenic and natural CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; exchange through the Strait of Gibraltar

Abstract. The exchange of both anthropogenic and natural inorganic carbon between the Atlantic Ocean and the Mediterranean Sea through Strait of Gibraltar was studied for a period of two years under the frame of the CARBOOCEAN project. A comprehensive sampling program was conducted, which was design to collect samples at eight fixed stations located in the Strait in successive cruises periodically distributed through the year in order to ensure a good spatial and temporal coverage. As a result of this monitoring, a time series namely GIFT (GIbraltar Fixed Time series) has been established, allowing the generation of an extensive data set of the carbon system parameters in the area. Data acquired during the development of nine campaigns were analyzed in this work. Total inorganic carbon concentration (CT) was calculated from alkalinity-pHT pairs and appropriate thermodynamic relationships, with the concentration of anthropogenic carbon (CANT) being also computed using two methods, the ΔC* and the TrOCA approach. Applying a two-layer model of water mass exchange through the Strait and using a value of −0.85 Sv for the average transport of the outflowing Mediterranean water recorded in situ during the considered period, a net export of inorganic carbon from the Mediterranean Sea to the Atlantic was obtained, which amounted to 25±0.6 Tg C yr−1. A net alkalinity output of 16±0.6 Tg C yr−1 was also observed to occur through the Strait. In contrast, the Atlantic water was found to contain a higher concentration of anthropogenic carbon than the Mediterranean water, resulting in a net flux of CANT towards the Mediterranean basin of 4.20±0.04 Tg C yr−1 by using the ΔC* method, which constituted the most adequate approach for this environment. A carbon balance in the Mediterranean was assessed and fluxes through the Strait are discussed in relation to the highly diverse estimates available in the literature for the area and the different approaches considered for CANT estimation. This work unequivocally confirms the relevant role of the Strait of Gibraltar as a controlling point for the biogeochemical exchanges occurring between the Mediterranean Sea and the Atlantic Ocean and emphasizes the influence of the Mediterranean basin in the carbon inventories of the North Atlantic.

Odin stratospheric proxy NO&amp;lt;sub&amp;gt;y&amp;lt;/sub&amp;gt; measurements and climatology

Abstract. Five years of OSIRIS (Optical Spectrograph and InfraRed Imager System) NO2 and SMR (Sub-millimetre and Millimetre Radiometer) HNO3 observations from the Odin satellite, combined with data from a photochemical box model, have been used to construct a stratospheric proxy NOy data set including the gases: NO, NO2, HNO3, 2×N2O5 and ClONO2. This Odin NOy climatology is based on all daytime measurements and contains monthly mean and standard deviation, expressed as mixing ratio or number density, as function of latitude or equivalent latitude (5° bins) on 17 vertical layers (altitude, pressure or potential temperature) between 14 and 46 km. Comparisons with coincident NOy profiles from the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) instrument were used to evaluate several methods to combine Odin observations with model data. This comparison indicates that the most appropriate merging technique uses OSIRIS measurements of NO2, scaled with model NO/NO2 ratios, to estimate NO. The sum of 2×N2O5 and ClONO2 is estimated from uncertainty-based weighted averages of scaled observations of SMR HNO3 and OSIRIS NO2. Comparisons with ACE-FTS suggest the precision (random error) and accuracy (systematic error) of Odin NOy profiles are about 15% and 20%, respectively. Further comparisons between Odin and the Canadian Middle Atmosphere Model (CMAM) show agreement to within 20% and 2 ppb throughout most of the stratosphere except in the polar vortices. The combination of good temporal and spatial coverage, a relatively long data record, and good accuracy and precision make this a valuable NOy product for various atmospheric studies and model assessments.

Shear Wave Velocity Structure of the Crust and Upper Mantle in Western China and Its Adjacent Area

AbstractIt's the first time that interstation method for Rayleigh wave is used to study the 3‐D VS structure in the crust and upper mantle beneath western China and its adjacent area. More than 3000 interstation great circle paths were processed to determine the phase velocity of the fundamental mode of Rayleigh wave, and finally 110 paths of high quality dispersion data were selected which show good spatial coverage in western China and its neighboring regions. Phase velocity maps from 15 s to 120 s were obtained by Tarantola's probability method. The shear wave velocity structure in the crust and upper mantle on 2° × 2° grid points in our studied area was inverted by Tarantola's least square method for nonlinear problem. Based on the physical property that the phase velocity of fundamental Rayleigh wave at period T is most sensitive to the VS structure around λ/3 depth, we provided a layer‐velocity self‐adaptive technique in the structure inversion, which can well accelerate converging speed and improve stability in the inversion. The main conclusions concerning the VS structure of the researched area are: (1) The western Qinghai‐Tibet Plateau shows very high VS value in the lower‐crust and top of the upper mantle, and the asthenosphere is not developed. But the eastern margin of the Qinghai‐Tibet Plateau clearly shows low‐velocity anomaly in the lower crust and top of the upper mantle, which probably created a southward extrusion channel for the low velocity crust material of the Qinghai‐Tibet Plateau along the eastern margin of the plateau through the western Sichuan and Yunnan region and then linking the low velocity zone in northern Burma. In the northeastern margin of the Qinghai‐Tibet Plateau, the VS of the lower crust is apparently lower than that of the mid‐crust. (2) The Lhasa block of the southern Qinghai‐Tibet Plateau has a high velocity lid in the upper mantle and from south to north the depth of the asthenosphere decreases from 130 km to 100 km, the thickness of the underlying asthenosphere increases from about 40 km to 80 km. The Qiangtang block of the northern Tibet shows lower velocity in lower crust, lacks high velocity lid in the upper mantle and displays much thicker asthenosphere. (3) The Tarim basin and Junggar basin both show high velocity structure in the upper mantle, asthenosphere layer does not clearly appear. Thickness and velocity of the lower crust in the Junggar basin is apparently higher than that in the Tarim basin. (4) Velocity in the lower crust and uppermost mantle beneath the western Mongolia plateau is apparently lower than its eastern part. In the middle‐western Mongolia plateau a thick and large scale asthenosphere is clearly shown. This thick asthenosphere gradually becomes thinner from middle to eastern Mongolia plateau and above which the higher velocity lid becomes thicker and thicker. Geological explanations are accomplished based on results of inversion.

New lessons on the Sudd hydrology learned from remote sensing and climate modeling

Abstract. Despite its local and regional importance, hydro-meteorological data on the Sudd (one of Africa's largest wetlands) is very scanty. This is due to the physical and political situation of this area of Sudan. The areal size of the wetland, the evaporation rate, and the influence on the micro and meso climate are still unresolved questions of the Sudd hydrology. The evaporation flux from the Sudd wetland has been estimated using thermal infrared remote sensing data and a parameterization of the surface energy balance (SEBAL model). It is concluded that the actual spatially averaged evaporation from the Sudd wetland over 3 years of different hydrometeorological characteristics varies between 1460 and 1935 mm/yr. This is substantially less than open water evaporation. The wetland area appears to be 70% larger than previously assumed when the Sudd was considered as an open water body. The temporal analysis of the Sudd evaporation demonstrated that the variation of the atmospheric demand in combination with the inter-annual fluctuation of the groundwater table results into a quasi-constant evaporation rate in the Sudd, while open water evaporation depicts a clear seasonal variability. The groundwater table characterizes a distinct seasonality, confirming that substantial parts of the Sudd are seasonal swamps. The new set of spatially distributed evaporation parameters from remote sensing form an important dataset for calibrating a regional climate model enclosing the Nile Basin. The Regional Atmospheric Climate Model (RACMO) provides an insight not only into the temporal evolution of the hydro-climatological parameters, but also into the land surface climate interactions and embedded feedbacks. The impact of the flooding of the Sudd on the Nile hydroclimatology has been analysed by simulating two land surface scenarios (with and without the Sudd wetland). The paper presents some of the model results addressing the Sudd's influence on rainfall, evaporation and runoff of the river Nile, as well as the influence on the microclimate. The paper presents a case study that confirms the feasibility of using remote sensing data (with good spatial and poor temporal coverage) in conjunction with a regional climate model. The combined model provides good temporal and spatial representation in a region characterized by extremely scarce ground data.

Environmental change and the arrival of people in the Australian region

Continuous pollen and charcoal records, predominantly from well dated marine sediments, provide a good spatial coverage of patterns of change in vegetation, climate and biomass burning within the northern Australian - southern Indonesian region through the late Quaternary period. Northern hemisphere ice volume and monsoon forcing is conspicuous on orbital timescales with general expansion of wetter communities under higher precipitation during interglacials and their contraction under drier glacials. However, this picture is regionally complicated by both southern hemisphere monsoon and long term El Nino - Southern Oscillation influences. The charcoal records suggest a complex pattern of burning with generally more frequent or intense fires during climate transitions and also during drier periods except when and where fuel availability became a limitation. Superimposed on this largely cyclical pattern is a trend, within the last 300,000 to 200,000 years, towards more open canopied vegetation and increased...

Mobile Voltammetric Laboratory for Ship-Board and Shore-Based Analyses of Dissolved Copper

Environmental Context. Determining concentrations of dissolved copper in seawater is of interest, because copper (i) affects the health of aquatic biota, and (ii) has the potential to act as a water mass tracer, a marker which can be used to follow the movement of water in oceans. In situ analyses of copper and other trace metals in seawater have become increasingly popular, because they circumvent potential contamination problems associated with sample collection, storage, and transport to off-site analysis locations. This paper describes the assembly of a low-cost, mobile laboratory utilizing adsorptive cathodic stripping voltammetry (AdCSV) for the real-time determination of total dissolved copper in surface waters. Abstract. The main advantages of using a mobile laboratory for the real-time analyses of copper in surface waters over classical discrete sampling include a reduction in the risk of sample contamination and significant savings in both time and money to the analyst. This paper outlines the development of a portable voltammetric laboratory, capable of deployment from ships or road vehicles, and an experimental method for the real time analysis of total dissolved copper in surface waters. It has been tested in estuarine and coastal waters to the west of Ireland and has proved suitable for the analysis of both fresh and marine waters. The system includes a trace metal-free sampling fish (for shipboard sampling), in-line filtration and UV-digestion units, and a voltammetric analyzer and electrode controlled by a portable PC. Analysis of samples is completed using adsorptive cathodic stripping voltammetry (AdCSV). Using this portable AdCSV laboratory, the high sample throughput – approximately three per hour with standard additions completed on every sample – means that for ship-board surveys good spatial coverage is possible without the need for time-consuming station stops. For van-based tidal surveys, the portable AdCSV laboratory is both straightforward and low in cost to deploy.

Indicators of Antarctic ozone depletion

Abstract. An assimilated data base of total column ozone measurements from satellites has been used to generate a set of indicators describing attributes of the Antarctic ozone hole for the period 1979 to 2003, including (i) daily measures of the area over Antarctica where ozone levels are below 150 DU, below 220 DU, more than 30% below 1979 to 1981 norms, and more than 50% below 1979 to 1981 norms, (ii) the date of disappearance of 150 DU ozone values, 220 DU ozone values, values 30% below 1979 to 1981 norms, and values 50% below 1979 to 1981 norms, for each year, (iii) daily minimum total column ozone values over Antarctica, and (iv) daily values of the ozone mass deficit based on a O3&lt;220 DU threshold. The assimilated data base combines satellite-based ozone measurements from 4 Total Ozone Mapping Spectrometer (TOMS) instruments, 3 different retrievals from the Global Ozone Monitoring Experiment (GOME), and data from 4 Solar Backscatter Ultra-Violet (SBUV) instruments. Comparisons with the global ground-based Dobson spectrophotometer network are used to remove offsets and drifts between the different data sets to produce a global homogeneous data set that combines the advantages of good spatial coverage of satellite data with good long-term stability of ground-based measurements. One potential use of the derived indices is detection of the expected recovery of the Antarctic ozone hole. The suitability of the derived indicators to this task is discussed in the context of their variability and their susceptibility to saturation effects which makes them less responsive to decreasing stratospheric halogen loading. It is also shown that if the corrections required to match recent Earth Probe TOMS measurements to Dobson measurements are not applied, some of the indictors are affected so as to obscure detection of the recovery of the Antarctic ozone hole.

The Geysers geothermal field: results from shear-wave splitting analysis in a fractured reservoir

SUMMARY Clear shear-wave splitting (SWS) is observed in 1757 high signal-to-noise ratio microearthquake seismograms recorded by two high density seismic arrays in the NW and the SE Geysers geothermal fields in California. The Geysers reservoir rocks within the study area are largely composed of lithic, low-grade metamorphism, well-fractured metagraywackes which commonly lack schistosity, warranting the general assumption that shear-wave splitting here is induced solely by stress-aligned fracturing in an otherwise isotropic medium. The high quality of observed shear-wave splitting parameters (fast shear-wave polarization directions and time delays) and the generally good data spatial coverage provide an unprecedented opportunity to demonstrate the applicability and limitations of the shear-wave splitting approach to successfully detect fracture systems in the shallow crust based on SWS field observations from a geothermal reservoir. Results from borehole stations in the NW Geysers indicate that polarization orientations range between N and N60E; while in the SE Geysers, ground surface stations show polarization directions that are generally N5E, N35E-to-N60E, N75E-to-N85E, and N20W-to-N55W. Crack orientations obtained from observed polarization orientations are in good agreement with independent field evidence, such as cracks in geological core data, tracer tests, locally mapped fractures, and the regional tectonic setting. Time delays range typically between 8 and 40 ms km −1 , indicating crack densities well within the norm of fractured reservoirs. The sizeable collection of high resolution shear-wave splitting parameters shows evidence of prevalent vertical to nearly vertical fracture patterns in The Geysers field. At some locations, however, strong variations of SWS parameters with ray azimuth and incident angle within the shear-wave window of seismic stations indicate the presence of more complex fracture patterns in the subsurface.

The August 2002 flood in Austria: sensitivity of precipitation forecast skill to areal and temporal averaging

The dependence of precipitation forecast skill on areal and temporal averaging during the August 2002 floods in Austria is investigated. Operational forecasts of the ALADIN limited area model are verified against precipitation analyses obtained from a combination of two different networks of surface stations: a hydrological network with good spatial coverage but limited temporal resolution (24 h), and a meteorological network with good temporal resolution (10 min) but limited spatial density. By applying averaging windows of varying size in space and time it is shown to what extent the forecast skill increases with decreasing forecast specificity. For the space and time scales studied an increase of the time window by a certain factor is found more efficient in reducing forecast error than an increase of area size by the same factor, reflecting well-known differences between the spatial and temporal autocorrelation of the precipitation process itself. Comparison with other moderate-to-heavy precipitation episodes of the period 1999-2002 shows close agreement, suggesting that the results are typical of such events in the region.

Novel Feature Extraction Technique for Fuzzy Relational Clustering of a Flexible Dopamine Reuptake Inhibitor

This paper describes a novel clustering methodology for classifying over 700 conformations of a flexible analogue of GBR 12909, a dopamine reuptake inhibitor that has completed phase I clinical trials as a treatment for cocaine abuse. The major aspect of the clustering methodology includes an efficient data-conditioning scheme where a systematic feature extraction procedure based on the structural properties of the molecule was used to reduce the associated feature space. This allowed region-specific clustering that focused on individual pharmacophore elements of the molecule. For clustering of the reduced feature set, the fuzzy clustering partitional method was utilized. Due to the relational nature of the feature data, fuzzy relational clustering was employed, and it successfully detected natural groups defined by rotational minima around N(sp(3))-C(sp(3)), O(sp(3))-C(sp(3)), and C(sp(3))-C(sp(2)) bonds. The proposed clustering methodology also employed several cluster validity measures, which corroborated the partitions produced by the clustering technique and agreed with the results of hierarchical clustering using the XCluster program. Representative structures which exhibited a reasonable spread of energies and showed good spatial coverage of the conformational space were identified for use as putative bioactive conformations in a future Comparative Molecular Field Analysis of GBR 12909 analogues. The clustering methodology developed here is capable of handling other computational chemistry problems, and the feature extraction technique can be easily generalized to other molecules.

Global distribution of the thermospheric total mass density derived from CHAMP

A global distribution of the thermospheric total mass density at 400 km altitude is derived from the high‐accuracy accelerometer on board the CHAMP satellite with good temporal and spatial coverage. It shows two interesting features. One is the anomalous distribution at low latitudes. Instead of maximizing at the dayside equator, the thermospheric density shows maxima at about 20°–25° geomagnetic latitude on both sides of the equator between 10 and 20 magnetic local time. This latitudinal distribution resembles fairly well the equatorial ionization anomaly, thus indicating strong magnetic control of the thermospheric mass density via ionosphere‐thermosphere coupling. The thermospheric density shows a secondary maximum at the nightside equator shortly before midnight, in reminiscence of the well‐known thermospheric midnight temperature maximum. Another feature to notice is that the thermospheric density is highly structured at high latitudes, with localized density enhancements possibly related to Joule/particle heating. This structure is, however, different from the cellular structure recognized by the National Center for Atmospheric Research thermosphere general circulation model at altitudes of 120–300 km. This indicates that the exact cellular structure may not necessarily extend to 400 km. A comparison between observations and the Mass Spectrometer Incoherent Scatter 1990 (MSIS90) model predictions shows that although the model describes the general structure of the observed density reasonably well, it misses the double peaks at low latitudes completely. This causes an underestimation of the total mass density by 15–20% in the crest region. At high latitudes an underestimation of 20–30% occurs in the midnight sector and the cusp region. Outside these localized areas the agreement between observations and predictions is quite good, with only ∼5% difference on average under quiet geomagnetic conditions.

Effects of Noise on Thorpe Scales and Run Lengths

Abstract Estimating the diapycnal mixing rate from standard CTD data by identifying overturning regions in the water column (the Thorpe-scale approach) provides good spatial and temporal coverage but is sometimes limited by instrument noise. This noise leads to spurious density inversions that are difficult to distinguish from real turbulent overturns. Previous efforts to eliminate noise may have overcorrected and hence underestimated the level of mixing. Here idealized density profiles are used to identify the magnitude and characteristics of overturning regions arising entirely from instrument noise, in order to establish a standard against which CTD data can be compared. The key nondimensional parameters are 1) the amplitude of the noise scaled by the density change over the section of profile considered, and 2) the number of data points in the section of profile. In some cases the product of these, which is equal to the amplitude of the noise scaled by the average density difference between consecutive measurements, is more useful than the second parameter. The probability distribution of “run length,” a useful diagnostic, varies significantly across this parameter space. Reasons for this are discussed, and it is shown that CTD data very rarely lie in a region of parameter space where comparison with the probability density function (PDF) of run lengths for a random uncorrelated series, or its rms value 6, is appropriate. The distribution of Thorpe displacements arising entirely from instrument noise, as well as the Thorpe scale and the statistics of density inversions, is also discussed. Analysis of CTD data from the interfaces of the thermohaline staircase in the deep Canada Basin illustrates how the results can be applied in practice to help to distinguish between signal and noise in marginal regimes. Density inversions seen in these data are shown to be no different from those that would result from instrument noise.