Large scale features and energetics of the hybrid subtropical low ‘Duck’ over the Tasman Sea

New aspects of the genesis and partial tropical transition of a rare hybrid subtropical cyclone on the eastern Australian coast are presented. The ‘Duck’ (March 2001) attracted more recent attention due to its underlying genesis mechanisms being remarkably similar to the first South Atlantic hurricane (March 2004). Here we put this cyclone in climate perspective, showing that it belongs to a class within the 1 % lowest frequency percentile in the Southern Hemisphere as a function of its thermal evolution. A large scale analysis reveals a combined influence from an existing tropical cyclone and a persistent mid-latitude block. A Lagrangian tracer showed that the upper level air parcels arriving at the cyclone’s center had been modified by the blocking. Lorenz energetics is used to identify connections with both tropical and extratropical processes, and reveal how these create the large scale environment conducive to the development of the vortex. The results reveal that the blocking exerted the most important influence, with a strong peak in barotropic generation of kinetic energy over a large area traversed by the air parcels just before genesis. A secondary peak also coincided with the first time the cyclone developed an upper level warm core, but with insufficient amplitude to allow for a full tropical transition. The applications of this technique are numerous and promising, particularly on the use of global climate models to infer changes in environmental parameters associated with severe storms.     

Circulatory Patterns of Air Pollutants within the Barcelona Air Basin in a Summertime situation: Lidar and Numerical Approaches

This work examines circulatory patterns of airpollutants in the area of Barcelona (Spain), a regionwith strong coastal and orographic influences. Thiswas achieved through exploitation ofelastic-backscatter lidar data and by numericalsimulation of the atmosphere with a meteorologicalmesoscale model (MEMO). Lidar data were acquired inJuly 1992 during a collaborative campaign between LosAlamos National Laboratory (LANL) and the PolytechnicUniversity of Catalonia (UPC). The lidar providedinformation about the distribution of aerosols and theprevailing winds, determined by application of amaximum cross-correlation algorithm toelastic-backscatter lidar data. Lidar winds are usedto evaluate high altitude winds simulated by themodel. This study showed that circulatory patterns inBarcelona are correlated with daytime convectivevertical mixing, sea-breeze circulations, and verticalforcing caused by mountain thermal and mechanicaleffects.     

Tracing the origins and propagation of pre-tropical storm Debby (2006) mesoscale convective systems using pattern recognition and image fusion

This study is focused on developing pattern recognition and image fusion techniques to trace the origins and propagation of the pre-tropical storm (pre-TS) Debby (2006) mesoscale convective systems (MCSs) and African easterly waves (AEWs) using satellite imagery. These MCSs could be generating over mountains in North Africa and going through complicated splitting and merging processes. Therefore, an objectively analyzed MCS movement is essential. This study presents a technique which traces extracted features to find the origin of TS Debby. This technique produces a fused image with the most relevant information from water vapor and infrared satellite images, segments the cloud top height satellite images by clustering clouds, and tracks clouds to determine the origin of TS Debby (2006). The presented technique could be applied to other AEWs and MCSs which lead to tropical cyclogenesis to improve the numerical weather prediction over data sparse areas, such as over eastern and central North Africa.     

Testing the robustness of semi-empirical sea level projections

We determine the parameters of the semi-empirical link between global temperature and global sea level in a wide variety of ways, using different equations, different data sets for temperature and sea level as well as different statistical techniques. We then compare projections of all these different model versions (over 30) for a moderate global warming scenario for the period 2000–2100. We find the projections are robust and are mostly within ±20% of that obtained with the method of Vermeer and Rahmstorf (Proc Natl Acad Sci USA 106:21527–21532, 2009), namely ~1 m for the given warming of 1.8°C. Lower projections are obtained only if the correction for reservoir storage is ignored and/or the sea level data set of Church and White (Surv Geophys, 2011) is used. However, the latter provides an estimate of the base temperature T ₀ that conflicts with the constraints from three other data sets, in particular with proxy data showing stable sea level over the period 1400–1800. Our new best-estimate model, accounting also for groundwater pumping, is very close to the model of Vermeer and Rahmstorf (Proc Natl Acad Sci USA 106:21527–21532, 2009).     

Observational and modelling studies of Amazonia interannual climate variability

The interannual variability of climate in the Amazon basin is studied using precipitation and river level anomalies observed near the March/April rainy season peak for the period 1980–86, supported by satellite imagery of tropical convection. Evaluation of this data in conjunction with the corresponding circulation and sea-surface temperature (SST) anomaly patterns indicates that abundant rainy seasons in Northern Amazonia are characterized by anomalously cold surface waters in the tropical eastern Pacific, and negative/positive SST anomalies in the tropical North/South Atlantic, accelerated Northeast trades and a southward displaced Intertropical Convergence Zone (ITCZ) over the Atlantic sector. Years with deficient rainfall show broadly opposite patterns.General circulation model (GCM) experiments using observed SST in three case studies were aimed at testing the teleconnections between SST and Amazon climate implied by the empirical analysis. The GCM-generated surface fields resemble the corresponding observers fields most closely over the tropical Pacific and, with one exception, over the tropical Atlantic as well. The modeled precipitation features, along the Northwest coast of South America, anomalies of opposite sign to the North and South of the equator, in agreement with observations and results from a different GCM. Similarities in simulations run from different initial conditions, but using the same global SST, indicate broad consistency in response to common boundary forcing.     

Atmospheric concentrations and deposition of heavy metals over the North Sea: A literature review

A literature review of the atmospheric concentration rates and dry and wet deposition fluxes of particulate Cd, Cr, Cu, Pb and Zn to the North Sea and adjacent areas is given. The results of direct measurements of dry and wet deposition fluxes are compared to indirect estimates and to modelling values. This work points out the large uncertainties in results of different studies on atmospheric input of trace elements into the North Sea. The current knowledge about the dependence of the deposition velocity upon the particle size and about the processes controlling wet deposition fluxes, and the quality and completeness of the emission data are still inadequate for describing the environmental cycle and impact of heavy metals in the North Sea.     

A methodology study of the validation of clouds in GCMs using ISCCP satellite observations

The cloudiness fields simulated by a general circulation model and a validation using the International Satellite Cloud Climatology Project (ISCCP) satellite observations are presented. An adapted methodology is developed, in which the issue of the sub-grid scale variability of the cloud fields, and how it may affect the comparison exercise, is considered carefully. In particular different assumptions about the vertical overlap of cloud layers are made, allowing us to reconstruct the cloud distribution inside a model grid column. Carrying out an analysis directly comparable to that of ISCCP then becomes possible. The relevance of this method is demonstrated by its application to the evaluation of the cloud schemes used in Laboratoire de Météoroligie Dynamique (LMD) general circulation model. We compare cloud properties, such as cloud-top height and cloud optical thickness, analysed by ISCCP and simulated by the LMD GCM. The results show that a direct comparison of simulated low cloudiness and that shown from satellites is not possible. They also reveal some model deficiencies concerning the cloud vertical distribution. Some of these features depend little on the cloud overlap assumption and may reveal inadequate parameterisation of the boundary layer mixing or the cloud water precipitation rate. High convective clouds also appear to be too thick.     

Identification and elimination of an inflow boundary computational solution in limited area model integrations

Abstract

The linearized non‐divergent barotropic vorticity equation in one dimension is used for the study of a problem associated with the specification of lateral boundaries in limited area models. This problem presents itself in the form of a “pillow” that builds up near the inflow boundary of the model. Linear analysis shows that this pillow can easily be eliminated. Linear integrations carried out with a corrector seem to be reasonably accurate.

Similar integrations with the linearized shallow water equations in one dimension also produce a pillow and the same corrector gives improved results. Additional runs are performed in order to show that some commonly used nesting strategies do not control this computational problem in a satisfactory manner. It seems that these strategies could be improved with an appropriate corrector.     

Assessment of phosphogypsum impact on the salt-marshes of the Tinto river (SW Spain): role of natural attenuation processes

About 120 Mton of phosphogypsum from the fertiliser industry were stack-piled on the salt-marshes of the Tinto river (Spain). This paper investigates the capacity of salt-marshes to attenuate contamination due to downward leaching from phosphogypsum. Solids and pore-waters were characterized at different depths of the pile to reach the marsh-ground. In superficial zones, metals were highly mobile, and no reduced sulphur was found. However, pollutant concentration decreased in the pore-water in deeper oxygen-restricted zones. Metal removal occurred by precipitation of newly formed sulphides, being this process main responsible for the contamination attenuation. Pyrite-S was the main sulphide component (up to 2528 mg/kg) and occurred as framboids, leading to high degrees of pyritization (up to 97%). The sulphidization reaction is Fe-limited; however, excess of acid-volatile sulphide over other metals cause precipitation of other sulphides, mainly of Cu and As. This decrease in metal mobility significantly minimises the impact of phosphogypsums on the salt-marshes.     

Variability of carbon dioxide flux from tropical (Cerrado) hydroelectric reservoirs

Hydroelectric reservoirs generate energy without significant combustion of fossil fuels. However, these systems can, potentially, emit greenhouse gases (GHG’s) at a rate which may be significant at the global scale, and, possible, co-equal, per kilowatt-hour, to that from conventional coal or oil-fired systems. Although much of the new construction of hydroelectric reservoirs is in the tropics, most of the data on GHG emissions comes from temperate regions. Further, much of the existing data on reservoir gas emissions comes from single sites, usually near the terminal dams. Large tropical reservoirs often involve the impoundments of river systems with complex morphology which in turn can cause spatial heterogeneity in gas flux. We evaluated spatial and seasonal variability in CO₂ concentrations and gas flux for five large (50–1,400 km²) reservoirs in the Cerrado region of Brazil. Most of data set (87% of all measurements) showed CO₂ supersaturation and net efflux to the atmosphere. There was as much or more variation in pCO₂ over space and among seasons. The large studied reservoirs showed different zones in terms of CO₂ emission because those fluxes are dependent on flooded biomass, watershed input of organic matter and dam operation regime. Here we demonstrate that the reservoirs in the Brazilian Cerrado have low rates of CO₂ emissions compared to existing global comparisons. Our results suggest that ignoring the spatial variability can lead to more than 25% error in total system gas flux.