1,564 research outputs found
Potential Vorticity Mixing in a Tangled Magnetic Field
A theory of potential vorticity (PV) mixing in a disordered (tangled)
magnetic field is presented. The analysis is in the context of -plane
MHD, with a special focus on the physics of momentum transport in the stably
stratified, quasi-2D solar tachocline. A physical picture of mean PV evolution
by vorticity advection and tilting of magnetic fields is proposed. In the case
of weak-field perturbations, quasi-linear theory predicts that the Reynolds and
magnetic stresses balance as turbulence Alfv\'enizes for a larger mean magnetic
field. Jet formation is explored quantitatively in the mean field-resistivity
parameter space. However, since even a modest mean magnetic field leads to
large magnetic perturbations for large magnetic Reynolds number, the physically
relevant case is that of a strong but disordered field. We show that numerical
calculations indicate that the Reynolds stress is modified well before
Alfv\'enization -- i.e. before fluid and magnetic energies balance. To
understand these trends, a double-average model of PV mixing in a stochastic
magnetic field is developed. Calculations indicate that mean-square fields
strongly modify Reynolds stress phase coherence and also induce a magnetic drag
on zonal flows. The physics of transport reduction by tangled fields is
elucidated and linked to the related quench of turbulent resistivity. We
propose a physical picture of the system as a resisto-elastic medium threaded
by a tangled magnetic network. Applications of the theory to momentum transport
in the tachocline and other systems are discussed in detail.Comment: 17 pages, 10 figures, 2 table
Three key lessons from Labour’s campaign – and how the party needs to change
Jeremy Corbyn has confounded his critics and increased Labour’s share of the vote in the General Election. But the party is some way from being able to command a parliamentary majority, says Patrick Diamond. Labour has articulated a vision of society which appeals to many young people and ‘left behind’ voters. Now the party needs to get over the intellectual defensiveness which has afflicted it for decades – and reach out to people in English constituencies who have no tribal loyalty to Labour
The trouble with Jeremy Corbyn: five tests the Labour leader is failing
Much of the Parliamentary Labour Party want to replace Jeremy Corbyn, and his popularity among the general public is low. Yet he was resoundingly re-elected by party members last autumn. Patrick Diamond assesses the Labour leader’s performance as an opposition leader according to five criteria, and concludes the risk of a Labour schism between ‘principles’ and ‘power’ – of the kind that rivened the party in the early 1980s – is considerable
Reducing the size of the civil service by a fifth at a time of myriad pressures hardly seems designed to achieve the government’s goals in a post-Brexit future
While bureaucratic headcount is a crude measure of government capability, Patrick Diamond explains the reasons why the recent proposal to cut 91,000 civil service jobs is particularly problematic
Cummings's thinking is a potent challenge to the Whitehall system - and is likely to be opposed
Patrick Diamond discusses Dominic Cummings's stated intent of imposing disruptive reforms on the civil service, and explains why his rhetoric may prove to be particularly counterproductive in a Conservative Government
A reformer from a bygone era: what the Cummings saga tells us about British governance
Patrick Diamond writes that the Cummings coronavirus row has wider implications for the machinery of British government. These revolve around the status of political advisers and the future of Cummings’s state reform visions
Groupthink, partisanship, and the end of Whitehall
Patrick Diamond writes that the traditional Whitehall model is being replaced by a system centred on politicised campaigning and run by partisan appointees. These institutional changes are unfolding at a critical moment in British politics, as Whitehall prepares to support Ministers in carrying out Brexit, and render the government machinery more vulnerable to groupthink and partisanship than ever before
What Michael Barber’s appointment tells us about Whitehall reform and the ‘science’ of delivery
In learning lessons from COVID-19 and preceding governance pathologies, it is clear a new approach is needed based on a fundamental overhaul of how policy change is undertaken, writes Patrick Diamond. He discusses what Sir Michael Barber’s recent appointment to carry out an audit of government effectiveness tells us about the government’s attitude towards reform, and whether Barber can help resolve the governance problems enveloping the British state
Dominic Cummings’s thinking on the civil service is a potent challenge to the Whitehall system – and is likely to be opposed
Patrick Diamond discusses Dominic Cummings’s stated intent of imposing disruptive reforms on the civil service, and explains why his rhetoric may prove to be particularly counterproductive in a Conservative Government
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