Contact CEH NORA team at noraceh@ceh.ac.ukThe NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. precipitation set a record (Fig. 3a). Sustained high precipitation amounts 60 during the whole winter led to this record, rather than a few very wet days, Human influence on climate in the 2014 Southern 61and none of the 5-day precipitation averages over the three winter months 62 was a record (Fig. 3b). Similarly, while Thames' daily peak river flows were 63 not exceptional, the 30-day peak flow was the second highest since 64 measurements began in 1883 ( Supplementary Fig. 10 to provide a conservative estimate of uncertainty. 106We consider January precipitation and SLP, with Southern England 107Precipitation (SEP) averaged over land grid points in 50º-52ºN, 6.5ºW-2ºE. 189In the large RCM ensemble, the best estimate for the overall change in risk of is an increase of 43%, with a range from no change to 164% increase 192 associated with uncertainty in the pattern of anthropogenic warming (Fig. 5d). rainfall that we simulate is less on timescales that dominate flooding in this 252 catchment, consistent with the mechanism being an increase in the frequency 253 of the zonal regime, and so, successions of strong but fast-moving storms. 254Outputs from CLASSIC are combined with information about the location of
Here we present an automated dust detection scheme using the Infrared (IR) channels of the Spinning Enhanced Visible and Infrared Imager (SEVIRI), carried on board Meteosat Second Generation (MSG) satellites, from which dust scheme images that are now widely used in Saharan dust studies are created. This provides an objective, readily reproducible and quick way to build up climatologies of dust presence which compares well with subjectively identified dust presence in the daytime hours. At nighttime the automated detection scheme is less reliable due to the strong diurnal cycle of surface temperatures. Our SEVIRI Dust Flag (SDF) is compared to Aerosol Optical Depth (AOD) from the surface and found to successfully and consistently identify moderate‐heavy dust outbreaks, although success rate is lower in the early morning and late evening. SDF corresponds to Absorbing Aerosol Index (AAI) from the Ozone Monitoring Instrument (OMI) that is also indicative of moderate‐heavy dust outbreaks across the central and western Sahara, but there are differences in the spatial patterns of climatologies created over a number of years that are likely to be due to the different sensitivities of the detection schemes. Despite these discrepancies, SDF and AAI both place dust hot spots in southern Algeria and across its southern borders with Mali and Niger, and SDF climatologies for June–August 2004–2010 reveal that there is a substantial degree of interannual variability in dust presence in the central and western Sahara in the boreal summer.
[1] Using a combination of idealized radiative transfer simulations and a case study from the first field campaign of the Saharan Mineral Dust Experiment (SAMUM) in southern Morocco, this paper provides a systematic assessment of the limitations of the widely used Spinning Enhanced Visible and Infrared Imager (SEVIRI) red-green-blue (RGB) thermal infrared dust product. Both analyses indicate that the ability of the product to identify dust, via its characteristic pink coloring, is strongly dependent on the column water vapor, the lower tropospheric lapse rate, and dust altitude. In particular, when column water vapor exceeds $20-25 mm, dust presence, even for visible optical depths of the order 0.8, is effectively masked. Variability in dust optical properties also has a marked impact on the imagery, primarily as a result of variability in dust composition. There is a moderate sensitivity to the satellite viewing geometry, particularly in moist conditions. The underlying surface can act to confound the signal seen through variations in spectral emissivity, which are predominantly manifested in the 8.7 mm SEVIRI channel. In addition, if a temperature inversion is present, typical of early morning conditions over the Sahara and Sahel, an increased dust loading can actually reduce the pink coloring of the RGB image compared to pristine conditions. Attempts to match specific SEVIRI observations to simulations using SAMUM measurements are challenging because of high uncertainties in surface skin temperature and emissivity. Recommendations concerning the use and interpretation of the SEVIRI RGB imagery are provided on the basis of these findings.Citation: Brindley, H., P. Knippertz, C. Ryder, and I. Ashpole (2012), A critical evaluation of the ability of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) thermal infrared red-green-blue rendering to identify dust events: Theoretical analysis,
[1] Observed river gauging data show significant evaporative losses from the land and water surface in the Niger inland delta. These losses indicate an important potential feedback between the land surface and atmosphere. Moreover, the reduction in river flow downstream of the wetland has clear implications for water management in the region and beyond. Here we have modeled the evaporative losses that occur over the Niger inland delta by adding an overbank flow parameterization to the Joint UK Land-Environment Simulator (JULES) land surface model. The hydrological component of this model comprises a probability-distributed model of soil moisture and runoff production coupled with a discrete approximation to the one-dimensional kinematic wave equation to route river water downslope. We use subgrid-resolution topographic data to derive a two-parameter frequency distribution of inundated areas for each grid box which we then employ to represent overbank inundation in the model. The model was driven using data from the ALMIP experiment (ALMIP stands for AMMA Land surface Model Intercomparison Project, wherein AMMA stands for African Monsoon Multidisciplinary Analyses). The model reproduces the salient features of the observed river flow and inundation patterns; these include significant evaporative losses from the inundated region accounting for doubling of the total land-atmosphere water flux during periods of greatest flooding. Our predictions of inundated area are in good agreement with observed estimates of the extent of inundation obtained using satellite infrared and microwave remote sensing.
In this paper, we outline a new objective dust source detection method for the central and western Sahara (CWS), based on the automated tracking of individual dust plumes in data from the Spinning Enhanced Visible and Infrared Imager, available every 15 mins. at ~0.03° spatial resolution. The method is used to map the origin of summertime dust storms in the CWS for June – August 2004 – 2010. It reveals the sources of these events in unprecedented detail, allowing for the identification of specific, highly active source areas. The study of collocated surface features reveals that many of the dominant sources are likely associated with paleolakes and outwash plains, many in close proximity to the Saharan mountains. Extensive nonsource areas are associated with low albedo and elevated terrain, pointing to the mountainous regions of the Sahara. Additionally, sand seas are not identified as important source areas, but their margins sometimes are. The automated tracking method also facilitates analysis of the transport direction of dust plumes from key source regions and the inference of emission mechanisms. It is found that there are two broad domains within the CWS: one in southwest Algeria and northwest Mali, characterized primarily by transport toward the southwest and very likely dominated by low‐level jets embedded in the northeasterly Harmattan winds; and a second in southern Algeria, northwest Niger, and northeast Mali where there is no preferred transport direction and a strong potential association between dust events and deep convection, pointing toward cold pool outflows as the likely deflation mechanism.
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