SUMMARYA multi-year simulation with an atmospheric general-circulation model (AGCM), the Unified Model, is shown to simulate the main features of seasonal variations in the concentrations of water vapour in the stratosphere-the so-called tape-recorder signal. An off-line transport model, utilizing winds from the AGCM, is used to synthesize the signal from local contributions. During June-July-August, the most significant localized contribution to the moist phase of the signal comes from an air stream emanating from the South-East Asian monsoon. The moist air does not enter the stratosphere immediately above the monsoon in a localized 'fountain'. Rather, the air stream moves southward, via the monsoon's upper level anticyclone, into the tropical stratosphere while moving steadily upwards across isentropic surfaces in a field of radiative heating in the tropical tropopause layer (TTL). As a result of this steady ascent during equatorward movement, not all the airstream is freeze dried in the cold cap of low temperatures which exists in the TTL above the monsoon. The water vapour mixing ratios of air entering the stratospheric tape-recorder are therefore not entirely set by the minimum temperatures near the equator, but in part by physical conditions outside the inner tropical region used to define the tape-recorder signal. During December-January-February, the flow near the tropopause is simpler. Dry air enters the stratosphere by slow upglide through the localized temperature minimum near the tropical tropopause over the western Pacific. The mixing ratios during the dry phase are set largely by freeze drying in this region. The simple tape-recorder model, which envisages that mixing ratios are set by the minimum temperature near the tropical tropopause is therefore an oversimplification.

SUMMARYThe sensitivity of a climate model's transport to the choice of numerical advection scheme is investigated using simulations of the stratospheric tape recorder. Signi cant differences are found between tracers advected with the Heun scheme (with centred spatial differencing) and tracers advected with a ux-limited total variation diminishing (TVD) scheme. The tape recorder simulated by the TVD scheme propagates upwards unrealistically fast: about three times faster than the tape recorder of the Heun scheme, even though the winds are identical. In contrast, the amplitude of the TVD scheme's tape recorder is more realistic than that of the Heun scheme, which is too strong in the middle stratosphere.Further off-line tracer experiments, using a family of conservative, upwind advection schemes, demonstrate how the tape recorder's phase speed decreases as the order of the polynomial representing the tracer's subgrid variation is increased. It is found that schemes with more implicit vertical diffusion than a quasi third-order scheme produce a tape recorder with unacceptably fast upwards propagation. The sensitivity can only be reproduced in a one-dimensional model when winds with strong variability are used, highlighting a limitation of the traditional advection tests that use constant winds. The experiments also show that the numerical oscillations produced by non-monotonic methods, including the Heun scheme, can arti cially strengthen the tape-recorder signal resulting in a unrealistic lack of attenuation with height. Finally, a full climate simulation using a higher-order, monotonic advection scheme is found to produce a tape recorder that is reasonably realistic, both in speed and amplitude.

I begin the paper by outlining one classic argument for the guise of the good: that we must think that desires represent their objects favourably in order to explain why they can make actions rational (Quinn 1995; Stampe 1987). But what exactly is the conclusion of this argument? Many have recently formulated the guise of the good as the view that desires are akin to perceptual appearances of the good (Oddie 2005; Stampe 1987; Tenenbaum 2007). But I argue that this view fails to capitalize on the above argument, and that the argument is better understood as favouring a view on which desires are belief-like states. I finish by addressing some countervailing claims made by Avery Archer (2016).

In this paper, I defend a new theory of normative reasons called reasons as good bases (RGB), according to which a normative reason to u is something that is a good basis for uing. The idea is that the grounds on which we do thingsbases-can be better or worse as things of their kind, and a normative reason-a good reason-is something that is just a good instance of such a ground. After introducing RGB, I clarify what it is to be a good basis, and argue that RGB has various attractive features: it has intuitive implications, makes good sense of the weights of reasons, and attractively explains the relationship between normative reasons and motivating reasons. I then briefly defend the view from objections and compare it to rivals. Finally, I sketch two possible implications of RGB: some kind of constitutivism, according to which the norms that govern us are explained by the nature of agency, and second, the claim that agents who do things for reasons generally do them for good reasons.

In this paper I first argue against one attractive formulation of the motivation argument, and against one attractive formulation of noncognitivism. I do so by example: I suggest that other-regarding normative judgments do not seem to have motivational powers and do not seem to be desires. After defending these two claims, I argue that other views can accommodate the motivational role of normative judgment without facing this objection. For example, desire-as-belief theories do so, since such theories only say that some normative judgments constitute desires, not that all such judgments do so. (I also briefly present similar reasoning in favor of the claim that desire-as-belief is superior to noncognitivism with respect to the Frege-Geach objection.) In short, I argue that, if we are seeking a theory that explains the motivational role of normative judgement, some theories are better than others insofar as they do so without committing to the claim that all normative judgements play such a motivational role.