title: Inflow reconnection solutions in incompressible visco-resistive plasmas

authors: Craig, Ian J.D.

subjects: magnetic reconnection

abstract: The development of a visco-resistive length scale for the thickness of a reconnecting current sheet would have significant consequences for the physics of magnetic reconnection in solar flares. In this paper, planar magnetic reconnection in an incompressible visco-resistive plasma is investigated analytically and numerically. Relaxation simulations are performed in an "open" geometry that allows material to enter and exit the reconnection volume. Solutions of two types are identified depending on the strength of the external flow that drives the reconnection. For sufficiently strong flows separate resistive and viscous layers develop in the reconnection region. In this case merging rates are found to be largely independent of viscosity. However, when the flow is too weak to produce a localized current layer, an equilibrium lacking any small-scale structure is obtained. The central conclusion is that neither of these steady-state solutions provide evidence of a visco-resistive length scale.

text: Inflow reconnection solutions in incompressible visco-resistive plasmas The development of a visco-resistive length scale for the thickness of a reconnecting current sheet would have significant consequences for the physics of magnetic reconnection in solar flares. In this paper, planar magnetic reconnection in an incompressible visco-resistive plasma is investigated analytically and numerically. Relaxation simulations are performed in an "open" geometry that allows material to enter and exit the reconnection volume. Solutions of two types are identified depending on the strength of the external flow that drives the reconnection. For sufficiently strong flows separate resistive and viscous layers develop in the reconnection region. In this case merging rates are found to be largely independent of viscosity. However, when the flow is too weak to produce a localized current layer, an equilibrium lacking any small-scale structure is obtained. The central conclusion is that neither of these steady-state solutions provide evidence of a visco-resistive length scale.

year: 2012

title: Sea-level change: Living with uncertainty

authors: de Lange, Willem P.

abstract: Sea level change is a naturally occurring process. Since the last glacial maximum, some 18,000 years ago, de-glaciation has taken place and this natural global warming has led to sea-level rise of on average 120 m or so. At some times, pulses of melt water coming from large peri-glacial lakes led to rates of sea-level rise as high as 3 m per century. The rate slowed down some 7000 years ago and since then has been naturally fluctuating by only a few meters. The remaining global sea-level rise has been about 20 cm in the 20th century. Has this led to global disasters? The answer is no. If the projected rise over the 21st century is double what was seen in the 20th, is it likely that it will result in global disasters? Again, the answer is most likely no; human ingenuity, innovation and engineering, and the proper material and financial resources should solve local problems if and when they arrive, as they have in the 20th century (see the Dutch example). 
In this short and accessible monograph, Willem de Lange and Robert Carter describe and explain sea-level change, including the many remaining uncertainties in our full understanding of what exactly drives this change, and discuss the implications, mainly regarding coastal management. The monograph is intended for policy makers, but it should be informative for any educated reader. De Lange and Carter analyse the causes of sea-level change, and describe how it has been measured – with tide gauges over the past 100 to 150 years and from satellites over the past 30 years. Their key message is to recall that sea-level change is a local phenomenon, with high variability and multiple causes. In the 20th century, for a global average rise of 20 cm, there has been sea-level rise of up to twice that value in some places, but in others a drop of the same amount! Because of the melting of a large former ice cap over the Baltic area, the Earth’s viscous mantle is slowly deforming and as a result sea-level is decreasing in the North of the British Isles at the same time as it is rising on the south coast. Moreover, we have known since Darwin and understood since the plate tectonics revolution that atolls in the Pacific form over slowly subsiding volcanoes and will eventually drown (but at a slower ‘geological’ rate, due to thermal subsidence of the lithosphere on which they stand). In any case, the global average has no practical value in local or regional coastal management.

text: Sea-level change: Living with uncertainty Sea level change is a naturally occurring process. Since the last glacial maximum, some 18,000 years ago, de-glaciation has taken place and this natural global warming has led to sea-level rise of on average 120 m or so. At some times, pulses of melt water coming from large peri-glacial lakes led to rates of sea-level rise as high as 3 m per century. The rate slowed down some 7000 years ago and since then has been naturally fluctuating by only a few meters. The remaining global sea-level rise has been about 20 cm in the 20th century. Has this led to global disasters? The answer is no. If the projected rise over the 21st century is double what was seen in the 20th, is it likely that it will result in global disasters? Again, the answer is most likely no; human ingenuity, innovation and engineering, and the proper material and financial resources should solve local problems if and when they arrive, as they have in the 20th century (see the Dutch example). 
In this short and accessible monograph, Willem de Lange and Robert Carter describe and explain sea-level change, including the many remaining uncertainties in our full understanding of what exactly drives this change, and discuss the implications, mainly regarding coastal management. The monograph is intended for policy makers, but it should be informative for any educated reader. De Lange and Carter analyse the causes of sea-level change, and describe how it has been measured – with tide gauges over the past 100 to 150 years and from satellites over the past 30 years. Their key message is to recall that sea-level change is a local phenomenon, with high variability and multiple causes. In the 20th century, for a global average rise of 20 cm, there has been sea-level rise of up to twice that value in some places, but in others a drop of the same amount! Because of the melting of a large former ice cap over the Baltic area, the Earth’s viscous mantle is slowly deforming and as a result sea-level is decreasing in the North of the British Isles at the same time as it is rising on the south coast. Moreover, we have known since Darwin and understood since the plate tectonics revolution that atolls in the Pacific form over slowly subsiding volcanoes and will eventually drown (but at a slower ‘geological’ rate, due to thermal subsidence of the lithosphere on which they stand). In any case, the global average has no practical value in local or regional coastal management.

year: 2014-01-15

title: Sociocultural realities: exploring new horizons by Angus Macfarlane, Sonja Macfarlane and Melinda Webber [Book Review]

authors: McNae, Rachel Elizabeth

abstract: This article reviews the book "Sociocultural realities: exploring new horizons", by Angus Macfarlane, Sonja Macfarlane and Melinda Webber

text: Sociocultural realities: exploring new horizons by Angus Macfarlane, Sonja Macfarlane and Melinda Webber [Book Review] This article reviews the book "Sociocultural realities: exploring new horizons", by Angus Macfarlane, Sonja Macfarlane and Melinda Webber

year: 2017