Potential vorticity in warm conveyor belt outflow

Warm conveyor belts (WCBs) are the main ascending air masses within extratropical cyclones. They often exhibit strong condensation and precipitation, associated with ascent on large scales or embedded convection. Most of the air outflows into the upper troposphere as part of a ridge. Such ridges are an integral part of Rossby waves propagating along the tropopause and are identified with a negative potential vorticity (PV) anomaly and associated anticyclonic circulation. It has been argued that diabatic modification of PV in WCBs has an important influence on the extent of the ridge, propagation of Rossby waves and weather impacts downstream. Following the coherent ensemble of trajectories defining a WCB, PV is expected to increase with time while below the level of maximum latent heating and then decrease as trajectories ascend above the heating maximum. In models, it is found that the net change is approximately zero, so that the average PV of the WCB outflow is almost equal to the PV of its inflow. Here, the conditions necessary for this evolution are explored analytically using constraints arising from the conservation of circulation. It is argued that the net PV change is insensitive to the details of diabatic processes and the PV maximum midway along a WCB depends primarily on the net diabatic transport of mass from the inflow to the outflow layer. The main effect of diabatic processes within a WCB is to raise the isentropic level of the outflow, rather than to modify PV.

Monuments should not be trusted exhibition

Monuments Should Not Be Trusted brings together over 30 leading artists and groups from the “golden years” of the Socialist Federal Republic of Yugoslavia - the period between the early 1960s and the mid 1980s. Over 100 artworks and artefacts illuminate the key contradictions of this single party state – built after WWII on socialist principles, yet immersed in “utopian consumerism.” This is the first time in the UK that the art of this period, which has attracted increasing attention, has been shown in the context of the social, economic and political conditions that gave rise to it. It draws on new and innovative research on this period, and features many of its most celebrated artists. The exhibition begins with the rise of consumerism, midway through President Josip Broz Tito’s 37 year presidency, and ends a few years after his death in 1980. As well as artists’ works in moving image, collage, photography, sculpture and painting, the exhibition encompasses music, TV clips and fascinating artefacts, such as gifts made by workers for President Tito’s birthday, and relay batons which were carried across the country and ceremonially presented to him.