We examine the effects of the limited size, mean value and aspect ratio of datasets when applying... more We examine the effects of the limited size, mean value and aspect ratio of datasets when applying the Radon Transform technique for the detection of alignments. We also introduce a Radon Transform equivalent to the Bartlett Periodogram approach, which has the advantage of improving the RT spectral estimates and can mitigate the aspect ratio problem. This technique is applied for the first time, in 3D, to study the characteristics of propagation and energy distribution of westward propagating meso-scale features in the south-east Indian Ocean. Results highlight a waveguide of enhanced westward propagating around 25°S.
Abstract. Ice growth in turbulent seawater is often accom-panied by the accumulation of frazil ic... more Abstract. Ice growth in turbulent seawater is often accom-panied by the accumulation of frazil ice crystals at its sur-face, forming a grease ice layer. The thickness and volume fraction of this ice layer play an important role in shaping the gradual transition from a loose to a solid ice cover, how-ever, observations are very sparse. Here we analyse an ex-tensive set of observations of frazil ice, grown in two parallel tanks with controlled wave conditions and thermal forcing, focusing on the first one to two days of grease ice accumu-lation. The following unresolved issues are addressed: (i) at which volume fraction the frazil crystals ’ rising process starts and how densely they accumulate at the surface, (ii) how the grease ice solid fraction and salinity evolve with time until solid ice starts to form and (iii) how do these conditions affect, and are affected by, waves and heat loss from the ice. We obtained estimates of the minimum ini-tial grease ice solid fraction (0.03–0.05...
Drones are increasingly being used globally for the support of healthcare programmes. Madagascar,... more Drones are increasingly being used globally for the support of healthcare programmes. Madagascar, Malawi and Senegal are among a group of early adopters piloting the use of bi-directional transport drones for health systems in sub-Saharan Africa. This article presents the experiences as well as the strengths, weaknesses, opportunities and threats (SWOT analysis) of these country projects. Methods for addressing regulatory, feasibility, acceptability, and monitoring and evaluation issues are presented to guide future implementations. Main recommendations for governments, implementers, drone providers and funders include (1) developing more reliable technologies, (2) thorough vetting of drone providers’ capabilities during the selection process, (3) using and strengthening local capacity, (4) building in-country markets and businesses to maintain drone operations locally, (5) coordinating efforts among all stakeholders under government leadership, (6) implementing and identifying fund...
Under turbulent conditions ice growth in sea water often occurs as tiny suspended frazil ice crys... more Under turbulent conditions ice growth in sea water often occurs as tiny suspended frazil ice crystals. When the turbulence is insufficient to keep the crystals in suspension, they may accumulate in a surface grease layer of pure ice and sea water. Here we give an account of this grease of low solid fraction and high salinity prior to its freeze-up into a solid ice cover. We provide equations for determining the bulk salinity, Sg, and solid ice volume fraction, ϕ s, of the grease layer by indirect and direct methods, review previous observations, and present new data. For the evolution of the solid fraction of accumulating grease ice we find (I) an early mode 0.08 < ϕ s < 0.12 and (II) a long-term packing limit of 0.28 < ϕ s < 0.31, which for sea water of salinity 34 corresponds to 29.5 < Sg <31.5 and 24 < Sg < 26, respectively. We associate (I) with a mechanical limit related to initial random packing of frazil crystals and (II) with a thermodynamic limit, be...
We present results from a laboratory tank study of ice growing from saline water in a wave field,... more We present results from a laboratory tank study of ice growing from saline water in a wave field, focusing on the transition from a predominantly frazil/grease-ice cover to a pancake-ice cover. Combining surface temperature observations with direct and indirect determinations of ice salinity and solid fraction, we describe the evolution of frazil- and pancake-ice area fraction, salinity and solid-ice volume fraction over the course of 1 day. In the investigated stage of transition, frazil ice surrounding the pancakes was found to have rather constant properties: a surface temperature 0.4–0.6 K below the freezing point of the underlying sea water, a salinity of 24–26 g kg–1 and a solid volume fraction of 0.25–0.29. the average salinity of young pancake ice, estimated from heat and salt budgets, decreased from 18 to 15 g kg–1, while average solid volume fractions increased from 0.6 to 0.7. the transition from frazil to pancake is estimated to take place when solid fractions reach 0.37...
The Polynya Signature Simulation Method (PSSM) is applied to Special Sensor Microwave/Imager obse... more The Polynya Signature Simulation Method (PSSM) is applied to Special Sensor Microwave/Imager observations from different Defense Meteorological Satellite Program spacecraft for 2002–05 to analyze the polynya area in the Ross Sea (Ross Ice Shelf polynya (RISP) and Terra Nova Bay polynya (TNBP)) and off the Adélie Coast (Mertz Glacier polynya (MGP)), Antarctica, on a sub-daily scale. The RISP and the MGP exhibit similar average total polynya areas. Major area changes (>10000km2; TNPB: >2000km2) occur over a range of 2–3 to 20 days in all regions. Sub-daily area changes are largest for the MGP (5800km2) and smallest for the TNBP (800km2), underlining the persistence of the forcing of the latter. ARTIST sea-ice (ASI) algorithm concentration maps obtained using 89 GHz Advanced Microwave Scanning Radiometer (AMSR-E) data are compared to PSSM maps, yielding convincing agreement in the average, similarly detailed winter polynya distribution. Average ASI algorithm ice concentrations ta...
We examine the effects of the limited size, mean value and aspect ratio of datasets when applying... more We examine the effects of the limited size, mean value and aspect ratio of datasets when applying the Radon Transform technique for the detection of alignments. We also introduce a Radon Transform equivalent to the Bartlett Periodogram approach, which has the advantage of improving the RT spectral estimates and can mitigate the aspect ratio problem. This technique is applied for the first time, in 3D, to study the characteristics of propagation and energy distribution of westward propagating meso-scale features in the south-east Indian Ocean. Results highlight a waveguide of enhanced westward propagating around 25°S.
Abstract. Ice growth in turbulent seawater is often accom-panied by the accumulation of frazil ic... more Abstract. Ice growth in turbulent seawater is often accom-panied by the accumulation of frazil ice crystals at its sur-face, forming a grease ice layer. The thickness and volume fraction of this ice layer play an important role in shaping the gradual transition from a loose to a solid ice cover, how-ever, observations are very sparse. Here we analyse an ex-tensive set of observations of frazil ice, grown in two parallel tanks with controlled wave conditions and thermal forcing, focusing on the first one to two days of grease ice accumu-lation. The following unresolved issues are addressed: (i) at which volume fraction the frazil crystals ’ rising process starts and how densely they accumulate at the surface, (ii) how the grease ice solid fraction and salinity evolve with time until solid ice starts to form and (iii) how do these conditions affect, and are affected by, waves and heat loss from the ice. We obtained estimates of the minimum ini-tial grease ice solid fraction (0.03–0.05...
Drones are increasingly being used globally for the support of healthcare programmes. Madagascar,... more Drones are increasingly being used globally for the support of healthcare programmes. Madagascar, Malawi and Senegal are among a group of early adopters piloting the use of bi-directional transport drones for health systems in sub-Saharan Africa. This article presents the experiences as well as the strengths, weaknesses, opportunities and threats (SWOT analysis) of these country projects. Methods for addressing regulatory, feasibility, acceptability, and monitoring and evaluation issues are presented to guide future implementations. Main recommendations for governments, implementers, drone providers and funders include (1) developing more reliable technologies, (2) thorough vetting of drone providers’ capabilities during the selection process, (3) using and strengthening local capacity, (4) building in-country markets and businesses to maintain drone operations locally, (5) coordinating efforts among all stakeholders under government leadership, (6) implementing and identifying fund...
Under turbulent conditions ice growth in sea water often occurs as tiny suspended frazil ice crys... more Under turbulent conditions ice growth in sea water often occurs as tiny suspended frazil ice crystals. When the turbulence is insufficient to keep the crystals in suspension, they may accumulate in a surface grease layer of pure ice and sea water. Here we give an account of this grease of low solid fraction and high salinity prior to its freeze-up into a solid ice cover. We provide equations for determining the bulk salinity, Sg, and solid ice volume fraction, ϕ s, of the grease layer by indirect and direct methods, review previous observations, and present new data. For the evolution of the solid fraction of accumulating grease ice we find (I) an early mode 0.08 < ϕ s < 0.12 and (II) a long-term packing limit of 0.28 < ϕ s < 0.31, which for sea water of salinity 34 corresponds to 29.5 < Sg <31.5 and 24 < Sg < 26, respectively. We associate (I) with a mechanical limit related to initial random packing of frazil crystals and (II) with a thermodynamic limit, be...
We present results from a laboratory tank study of ice growing from saline water in a wave field,... more We present results from a laboratory tank study of ice growing from saline water in a wave field, focusing on the transition from a predominantly frazil/grease-ice cover to a pancake-ice cover. Combining surface temperature observations with direct and indirect determinations of ice salinity and solid fraction, we describe the evolution of frazil- and pancake-ice area fraction, salinity and solid-ice volume fraction over the course of 1 day. In the investigated stage of transition, frazil ice surrounding the pancakes was found to have rather constant properties: a surface temperature 0.4–0.6 K below the freezing point of the underlying sea water, a salinity of 24–26 g kg–1 and a solid volume fraction of 0.25–0.29. the average salinity of young pancake ice, estimated from heat and salt budgets, decreased from 18 to 15 g kg–1, while average solid volume fractions increased from 0.6 to 0.7. the transition from frazil to pancake is estimated to take place when solid fractions reach 0.37...
The Polynya Signature Simulation Method (PSSM) is applied to Special Sensor Microwave/Imager obse... more The Polynya Signature Simulation Method (PSSM) is applied to Special Sensor Microwave/Imager observations from different Defense Meteorological Satellite Program spacecraft for 2002–05 to analyze the polynya area in the Ross Sea (Ross Ice Shelf polynya (RISP) and Terra Nova Bay polynya (TNBP)) and off the Adélie Coast (Mertz Glacier polynya (MGP)), Antarctica, on a sub-daily scale. The RISP and the MGP exhibit similar average total polynya areas. Major area changes (>10000km2; TNPB: >2000km2) occur over a range of 2–3 to 20 days in all regions. Sub-daily area changes are largest for the MGP (5800km2) and smallest for the TNBP (800km2), underlining the persistence of the forcing of the latter. ARTIST sea-ice (ASI) algorithm concentration maps obtained using 89 GHz Advanced Microwave Scanning Radiometer (AMSR-E) data are compared to PSSM maps, yielding convincing agreement in the average, similarly detailed winter polynya distribution. Average ASI algorithm ice concentrations ta...
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