Separating the dynamical effects of climate change and ozone depletion. Part I: Southern Hemisphere stratosphere

A version of the Canadian Middle Atmosphere Model that is coupled to an ocean is used to investigate the separate effects of climate change and ozone depletion on the dynamics of the Southern Hemisphere (SH) stratosphere. This is achieved by performing three sets of simulations extending from 1960 to 2099: 1) greenhouse gases (GHGs) fixed at 1960 levels and ozone depleting substances (ODSs) varying in time, 2) ODSs fixed at 1960 levels and GHGs varying in time, and 3) both GHGs and ODSs varying in time. The response of various dynamical quantities to theGHGand ODS forcings is shown to be additive; that is, trends computed from the sum of the first two simulations are equal to trends from the third. Additivity is shown to hold for the zonal mean zonal wind and temperature, the mass flux into and out of the stratosphere, and the latitudinally averaged wave drag in SH spring and summer, as well as for final warming dates. Ozone depletion and recovery causes seasonal changes in lower-stratosphere mass flux, with reduced polar downwelling in the past followed by increased downwelling in the future in SH spring, and the reverse in SH summer. These seasonal changes are attributed to changes in wave drag caused by ozone-induced changes in the zonal mean zonal winds. Climate change, on the other hand, causes a steady decrease in wave drag during SH spring, which delays the breakdown of the vortex, resulting in increased wave drag in summer

Seasonality in Southeast Asian stock markets: some new evidence on day-of-the-week effects

This paper examines the evidence for a day-of-the-week effect in five Southeast Asian stock markets: South Korea, Malaysia, the Philippines, Taiwan and Thailand. Findings indicate significant seasonality for three of the five markets. Market risk, proxied by the return on the FTA World Price Index, is not sufficient to explain this calendar anomaly. Although an extension of the risk-return equation to incorporate interactive seasonal dummy variables can explain some significant day-of-the-week effects, market risk alone appears insufficient to characterize this phenomenon.

Effects of the 5-HT(1A) agonist (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) on cocaine choice in cynomolgus monkeys

Drugs that alter brain serotonin (5-HT) function can modulate the behavioral effects of cocaine, but the underlying receptor mechanisms are poorly understood. The present study examined the effects of the selective 5-HT1A receptor agonist (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, 0.01-0.1 mg/kg, i.v.) on cocaine self-administration in the context of a choice procedure. Five adult male cynomolgus monkeys self-administered cocaine (saline, 0.003-0.03 mg/kg per injection) under a concurrent fixed-ratio 50 schedule of food (1-g banana-flavored pellets) and cocaine presentation. Allocation of responses to the cocaine-associated lever (cocaine choice) increased in a dose-related manner from < or =20% of total responses when saline or 0.003 mg/kg per injection cocaine was the alternative to food to > or =75% when 0.03 mg/kg per injection cocaine was available. In four of five monkeys, when choice was between a low cocaine dose and food, 0.01 mg/kg 8-OH-DPAT increased injection-lever responding. At cocaine doses which occasioned > or =75% cocaine choice, 8-OH-DPAT did not alter response allocation. In the fifth monkey, 8-OH-DPAT only decreased injection-lever responding. When choice was between saline and food, 8-OH-DPAT did not reliably shift responding to the injection lever, except at doses that disrupted operant performance. These results suggest that a 5-HT1A receptor agonist can increase the reinforcing strength of a low cocaine dose relative to a concurrently available non-drug reinforcer.

Effects of drugs that potentiate GABA on extinction of positively-reinforced operant behaviour

Extinction following positively reinforced operant conditioning reduces response frequency, at least in part through the aversive or frustrative effects of non-reinforcement. According to J.A. Gray's theory, non-reinforcement activates the behavioural inhibition system which in turn causes anxiety. As predicted, anxiolytic drugs including benzodiazepines affect the operant extinction process. Recent studies have shown that reducing GABA-mediated neurotransmission retards extinction of aversive conditioning. We have shown in a series of studies that anxiolytic compounds that potentiate GABA facilitate extinction of positively reinforced fixed-ratio operant behaviour in C57B1/6 male mice. This effect does not occur in the early stages of extinction, nor is it dependent on cumulative effects of the compound administered. Potentiation of GABA at later stages has the effect of increasing sensitivity to the extinction contingency and facilitates the inhibition of the behaviour that is no longer required. The GABAergic hypnotic, zolpidem, has the same selective effects on operant extinction in this procedure. The effects of zolpidem are not due to sedative action. There is evidence across our series of experiments that different GABA-A subtype receptors are involved in extinction facilitation and anxiolysis. Consequently, this procedure may not be an appropriate model for anxiolytic drug action, but it may be a useful technique for analysing the neural bases of extinction and designing therapeutic interventions in humans where failure to extinguish inappropriate behaviours can lead to pathological conditions such as post-traumatic stress disorder.

Effects of chlordiazepoxide on extinction and re-acquisition of operant behaviour in mice

Relatively little is known about the role of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) in extinction of appetitively motivated tasks. The benzodiazepine (BZ) chlordiazepoxide (CDP) was administered during extinction and re-acquisition of lever pressing by mice following food reinforced discrete-trial fixed-ratio 5 (FR-5) training. Typical FR behaviour was established during baseline training and persisted for several extinction sessions. There were 15 extinction sessions in all, followed by six re-acquisition sessions where food reinforcement was re-introduced. In a 2x2x2 between-group design, CDP (15 mg/kg) or vehicle injections were given prior to either the last two food reinforcement sessions and the first 10 extinction sessions, or the final five extinction sessions, or the six re-acquisition sessions. Initially CDP had no effect on the rate of extinction, but after several extinction sessions it significantly facilitated it. Surprisingly, if CDP was administered only after several sessions of extinction, it immediately produced facilitation. Thus the delayed effects of CDP are not due to drug accumulation. These data suggest that some neural change must occur before CDP can affect extinction processes. In re-acquisition sessions, CDP facilitated the reinstatement of food-reinforced lever pressing. Implications for neural and behavioural accounts of operant extinction are discussed.

Transient atmospheric response to interactive SST anomalies

The transient atmospheric response to interactive SST anomalies in the midlatitudes is investigated using a three-layer QG model coupled in perpetual winter conditions to a slab oceanic mixed layer in the North Atlantic. The SST anomalies are diagnosed from a coupled run and prescribed as initial conditions, but are free to evolve. The initial evolution of the atmospheric response is similar to that obtained with a prescribed SST anomaly, starting as a quasi-linear baroclinic and then quickly evolving into a growing equivalent barotropic one. Because of the heat flux damping, the SST anomaly amplitude slowly decreases, albeit with little change in pattern. Correspondingly, the atmospheric response only increases until it reaches a maximum amplitude after about 1–3.5 months, depending on the SST anomaly considered. The response is similar to that at equilibrium in the fixed SST case, but it is 1.5–2 times smaller, and then slowly decays away.

The importance of vertical velocity variability for estimates of the indirect aerosol effects

The activation of aerosols to form cloud droplets is dependent upon vertical velocities whose local variability is not typically resolved at the GCM grid scale. Consequently, it is necessary to represent the subgrid-scale variability of vertical velocity in the calculation of cloud droplet number concentration. This study uses the UK Chemistry and Aerosols community model (UKCA) within the Hadley Centre Global Environmental Model (HadGEM3), coupled for the first time to an explicit aerosol activation parameterisation, and hence known as UKCA-Activate. We explore the range of uncertainty in estimates of the indirect aerosol effects attributable to the choice of parameterisation of the subgrid-scale variability of vertical velocity in HadGEM-UKCA. Results of simulations demonstrate that the use of a characteristic vertical velocity cannot replicate results derived with a distribution of vertical velocities, and is to be discouraged in GCMs. This study focuses on the effect of the variance (σw2) of a Gaussian pdf (probability density function) of vertical velocity. Fixed values of σw (spanning the range measured in situ by nine flight campaigns found in the literature) and a configuration in which σw depends on turbulent kinetic energy are tested. Results from the mid-range fixed σw and TKE-based configurations both compare well with observed vertical velocity distributions and cloud droplet number concentrations. The radiative flux perturbation due to the total effects of anthropogenic aerosol is estimated at −1.9 W m−2 with σw = 0.1 m s−1, −2.1 W m−2 with σw derived from TKE, −2.25 W m−2 with σw = 0.4 m s−1, and −2.3 W m−2 with σw = 0.7 m s−1. The breadth of this range is 0.4 W m−2, which is comparable to a substantial fraction of the total diversity of current aerosol forcing estimates. Reducing the uncertainty in the parameterisation of σw would therefore be an important step towards reducing the uncertainty in estimates of the indirect aerosol effects. Detailed examination of regional radiative flux perturbations reveals that aerosol microphysics can be responsible for some climate-relevant radiative effects, highlighting the importance of including microphysical aerosol processes in GCMs.

A regime-dependent parametrization of subgrid-scale cloud water content variability

The subgrid-scale spatial variability in cloud water content can be described by a parameter f called the fractional standard deviation. This is equal to the standard deviation of the cloud water content divided by the mean. This parameter is an input to schemes that calculate the impact of subgrid-scale cloud inhomogeneity on gridbox-mean radiative fluxes and microphysical process rates. A new regime-dependent parametrization of the spatial variability of cloud water content is derived from CloudSat observations of ice clouds. In addition to the dependencies on horizontal and vertical resolution and cloud fraction included in previous parametrizations, the new parametrization includes an explicit dependence on cloud type. The new parametrization is then implemented in the Global Atmosphere 6 (GA6) configuration of the Met Office Unified Model and used to model the effects of subgrid variability of both ice and liquid water content on radiative fluxes and autoconversion and accretion rates in three 20-year atmosphere-only climate simulations. These simulations show the impact of the new regime-dependent parametrization on diagnostic radiation calculations, interactive radiation calculations and both interactive radiation calculations and in a new warm microphysics scheme. The control simulation uses a globally constant f value of 0.75 to model the effect of cloud water content variability on radiative fluxes. The use of the new regime-dependent parametrization in the model results in a global mean which is higher than the control's fixed value and a global distribution of f which is closer to CloudSat observations. When the new regime-dependent parametrization is used in radiative transfer calculations only, the magnitudes of short-wave and long-wave top of atmosphere cloud radiative forcing are reduced, increasing the existing global mean biases in the control. When also applied in a new warm microphysics scheme, the short-wave global mean bias is reduced.