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Dall'Olmo G.,Plymouth Marine Laboratory | Dall'Olmo G.,National Center for Earth Observation | Mork K.A.,Norwegian Institute of Marine Research | Mork K.A.,Center for Climate Dynamics
Geophysical Research Letters | Year: 2014

Despite its fundamental role in controlling the Earth's climate, present estimates of global organic carbon export to the deep sea are affected by relatively large uncertainties. These uncertainties are due to lack of observations as well as disagreement among methods and assumptions used to estimate carbon export. Complementary observations are thus needed to reduce these uncertainties. Here we show that optical backscattering measured by Bio-Argo floats can detect a seasonal carbon export flux in the Norwegian Sea. This export was most likely due to small particles (i.e., 0.2-20 μm), was comparable to published export values, and contributed to long-term carbon sequestration. Our findings highlight the importance of small particles and of physical mixing in the biological carbon pump and support the use of autonomous platforms as tools to improve our mechanistic understanding of the ocean carbon cycle. Key Points Bio-Argo floats can track small particles in the mesopelagic region Export fluxes from small particles were significant Small particles contributed to long-term carbon sequestration ©2014. The Authors. Source

Taylor C.M.,UK Center for Ecology and Hydrology | Taylor C.M.,National Center for Earth Observation
Geophysical Research Letters | Year: 2015

Feedbacks between soil moisture and precipitation are important for understanding hydroclimatic variability in many regions. However, much uncertainty remains about how land surface fluxes influence the initiation of deep convection locally. While some studies consider only atmospheric and soil profiles, in a one-dimensional sense, others have argued that horizontal variability in fluxes plays an important role in convective triggering, via mesoscale circulations. This paper presents the first comprehensive observational analysis over Europe linking convective initiation to soil moisture, based on satellite observations of cloud top and land surface temperature, and soil moisture. The results show that convective initiations are favored on the downwind side of dry surfaces, close to wetter areas. The signal is clearest following dry periods and under light winds, consistent with forcing by a mesoscale circulation. Overall, the detected signal in Europe is weaker than in previous Sahelian analysis, but key spatial characteristics are essentially the same. ©2015. The Authors. Source

Wooster M.J.,Kings College London | Wooster M.J.,National Center for Earth Observation | Perry G.L.W.,University of Auckland | Zoumas A.,Kings College London
Biogeosciences | Year: 2012

Borneo (Indonesia) is Earth's third largest island, and the location of both extensive areas of rainforest and tropical peatlands. It is the site of both regular (seasonal) biomass burning associated with deforestation, land cover change and agricultural production preparations, and occasional, but much more severe, extreme fire episodes releasing enormous volumes of carbon from burning vegetation and peat. These extreme fire episodes are believed to result from anthropogenic practices related to (the still ongoing) forest degradation and clearance activities, whose impact with regard to fire is magnified by the effects of El Niño related drought. Since 2000, data from the MODIS Earth Observation satellite instruments have been used to study fire on Borneo, but earlier large fire events remain less well documented. Here we focus on a series of large fire episodes prior to the MODIS era, and specifically a 20 yr period covering both the two strongest El Niño events on record (1997-1998 and 1982-1983), along with an unprecedented series of more frequent, but weaker, El Niños. For the five El Niños occurring between 1980 and 2000, we develop quantitative measures of the fire activity across Borneo based on active fire counts derived from NOAA AVHRR Global Area Coverage (GAC) Earth Observation satellite data. We use these metrics to investigate relationships between the strength and timing of the El Niño event, the associated drought, and the fire activity. During each El Niño, we find areas of major fire activity confined within two or three fire sub-seasons (separated by monsoons) and focused in parts of South and Central Kalimantan, and sometimes also in East and/or West Kalimantan. For each El Niño we investigate various lag correlations, and find relationships of similar strength between monthly rainfall deficit and fire, but of more variable strength between indices of El Niño strength (ENSO indices) and rainfall deficit. The two strongest El Niño episodes (1982-1983 and 1997-1998) are accompanied by the most abundant fires (two and three times the active fire count seen in the next largest fire year), and the strongest correlations between measures of El Niño strength, rainfall and fire. We find the most significant positive statistical association between an ENSO index and fire activity to be that between the 16-month (first and second fire sub-seasons) cumulative NINO3 anomaly and the simultaneously recorded active fire count (r Combining double low line 0.98, based on the five El Niño episodes between 1980 and 2000), although we find a negative association of equal strength between the cumulative NINO4 index and active fire count when considered over the entire two year duration of each El Niño episode (first, second and third fire sub-seasons). Our results confirm that the El Niño phenomenon, via its effect on precipitation, is a primary large-scale, short-term climatic factor that has a strong control on the magnitude of the fire activity resulting from the numerous land cover changes, agricultural preparation practices and human-caused ignitions occurring annually across Borneo. The results also suggest that ENSO forecasting maybe a realistic means of estimating the extent and magnitude of this fire activity some months in advance, thus offering some potential for forecasting effects on the remaining forest and peatland resource and the regional atmosphere. © 2012 Author(s). Source

Smith T.E.L.,Kings College London | Wooster M.J.,Kings College London | Wooster M.J.,National Center for Earth Observation | Tattaris M.,Kings College London | Griffith D.W.T.,University of Wollongong
Atmospheric Measurement Techniques | Year: 2011

When compared to established point-sampling methods, Open-Path Fourier Transform Infrared (OP-FTIR) spectroscopy can provide path-integrated concentrations of multiple gases simultaneously, in situ and near-continuously. The trace gas pathlength amounts can be retrieved from the measured IR spectra using a forward model coupled to a non-linear least squares fitting procedure, without requiring "background" spectral measurements unaffected by the gases of interest. However, few studies have investigated the accuracy of such retrievals for CO2, CH4 and CO, particularly across broad concentration ranges covering those characteristic of ambient to highly polluted air (e.g. from biomass burning or industrial plumes). Here we perform such an assessment using data collected by a field-portable FTIR spectrometer. The FTIR was positioned to view a fixed IR source placed at the other end of an IR-transparent cell filled with the gases of interest, whose target concentrations were varied by more than two orders of magnitude. Retrievals made using the model are complicated by absorption line pressure broadening, the effects of temperature on absorption band shape, and by convolution of the gas absorption lines and the instrument line shape (ILS). Despite this, with careful model parameterisation (i.e. the optimum wavenumber range, ILS, and assumed gas temperature and pressure for the retrieval), concentrations for all target gases were able to be retrieved to within 5%. Sensitivity to the aforementioned model inputs was also investigated. CO retrievals were shown to be most sensitive to the ILS (a function of the assumed instrument field-of-view), which is due to the narrow nature of CO absorption lines and their consequent sensitivity to convolution with the ILS. Conversely, CO2 retrievals were most sensitive to assumed atmospheric parameters, particularly gas temperature. Our findings provide confidence that FTIR-derived trace gas retrievals of CO2, CH4 and CO based on modeling can yield results with high accuracies, even over very large (many order of magnitude) concentration ranges that can prove difficult to retrieve via standard classical least squares (CLS) techniques. With the methods employed here, we suggest that errors in the retrieved trace gas concentrations should remain well below 10%, even with the uncertainties in atmospheric pressure and temperature that might arise when studying plumes in more difficult field situations (e.g. at uncertain altitudes or temperatures). © Author(s) 2011. Source

Dacre H.F.,University of Reading | Hawcroft M.K.,University of Reading | Stringer M.A.,University of Reading | Hodges K.I.,National Center for Earth Observation
Bulletin of the American Meteorological Society | Year: 2012

Extratropical cyclones play a significant role in determining the day-to-day weather conditions in many parts of the world through their associated wind and precipitation patterns. The atlas has been created to explore the mean structure and evolution of the 200 most intense North Atlantic cyclones identified in 20 winters of the ERAInterim reanalysis data. The method used to create the composite fields is described in section 2. In sections 3 and 4, vertical and horizontal composites of cyclone structure for cyclones generated in the North Atlantic regions are used to subjectively identify features such as the relative positions of cold, warm, and occluded fronts and their associated wind and cloud patterns. At the same time, development of a closed isobar forms and the central pressure falls; cyclonic circulation and system-relative wind speeds around the cyclone center increase. The system-relative winds are computed by subtracting the propagation speed of the cyclone from the gridded winds for each individual cyclone before compositing. Source

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