Mechanisms of midlatitude cross-tropopause transport using a potential vorticity budget approach

[ 1] A potential vorticity (PV) budget method has been used to attribute vertical transport across the near-tropopause ( 1 PVU surface) in extratropical weather systems to radiative, latent heating and cooling, and mixing processes. Sources and sinks of PV due to nonconservative processes are calculated online and advected as passive tracers. There is reasonable agreement between the spatial distribution of transport determined from the PV budget method and the transport across the 1 - 2 PVU zone from a passive tracer and trajectories, but different aspects of exchange can be diagnosed with each method. Stratosphere-to-troposphere transport occurred in the broad upper level PV anomalies and was attributed mainly to latent heating and cooling processes; troposphere-to-stratosphere transport occurred toward the tail of a PV filament and in a ridge region and was attributed mainly to radiative processes. The contribution of mixing processes to transport was comparatively small. Using the PV budget method, the domain integrated exchange across the 1 PVU surface was from stratosphere to troposphere, and the magnitude of 1 x 10(15) kg over a 2 day winter integration in a large North Atlantic domain is consistent with stratosphere-troposphere exchange calculations from other studies. This exchange arises from an approximate balance between the dominant stratosphere-to-troposphere transport due to latent heating and cooling processes and troposphere-to-stratosphere transport due to radiative processes. The direction of transport across the tropopause in a fold was found to be critically dependent on the PV surface considered to represent the tropopause.

Assessment of the consistency of near-infrared water vapor line intensities using high-spectral-resolution ground-based Fourier transform measurements of solar radiation

Calculations of the absorption of solar radiation by atmospheric gases, and water vapor in particular, are dependent on the quality of databases of spectral line parameters. There has been increasing scrutiny of databases such as HITRAN in recent years, but this has mostly been performed on a band-by-band basis. We report nine high-spectral-resolution (0.03 cm(-1)) measurements of the solar radiation reaching the surface in southern England over the wave number range 2000 to 12,500 cm(-1) (0.8 to 5 mm) that allow a unique assessment of the consistency of the spectral line databases over this entire spectral region. The data are assessed in terms of the modeled water vapor column that is required to bring calculations and observations into agreement; for an entirely consistent database, this water vapor column should be constant with frequency. For the HITRAN01 database, the spread in water vapor column is about 11%, with distinct shifts between different spectral regions. The HITRAN04 database is in significantly better agreement (about 5% spread) in the completely updated 3000 to 8000 cm(-1) spectral region, but inconsistencies between individual spectral regions remain: for example, in the 8000 to 9500 cm(-1) spectral region, the results indicate an 18% (+/- 1%) underestimate in line intensities with respect to the 3000 to 8000 cm(-1) region. These measurements also indicate the impact of isotopic fractionation of water vapor in the 2500 to 2900 cm(-1) range, where HDO lines dominate over the lines of the most abundant isotope of H2O.

Development of smart variable stiffness actuators using polymer hydrogels

In this work, compliant actuators are developed by coupling braided structures and polymer gels, able to produce work by controlled gel swelling in the presence of water. A number of aspects related to the engineering of gel actuators were studied, including gel selection, modelling and experimentation of constant force and constant displacement behaviour, and response time. The actuator was intended for use as vibration neutralizer: with this aim, generation of a force of 10 N in a time not exceeding a second was needed. Results were promising in terms of force generation, although response time was still longer than required. In addition, the easiest way to obtain the reversibility of the effect is still under discussion: possible routes for improvement are suggested and will be the object of future work.