Abstract. An empirical technique for retrieving profiles of the square of the Brunt-Väisälä frequency, ω 2 B , from MST radar return signal power is presented. The validity of the technique, which is applied over the altitude range 1.0-15.7 km, is limited to those altitudes at which the humidity contributions to the mean vertical gradient of generalised potential refractive index, M, can be ignored. Although this is commonly assumed to be the case above the first few kilometres of the atmosphere, it is shown that humidity contributions can be significant right up to the tropopause level. In specific circumstances, however, the technique is valid over large sections of the troposphere. Comparisons of radarand (balloon-borne) radiosonde-derived ω 2 B profiles are typically quantitatively and qualitatively well matched. However, the horizontal separation between the radar and the radiosondes (which were launched at the radar site) increases with increasing altitude. Under conditions of mountain wave activity, which can be highly localised, large discrepancies can occur at lower-stratospheric altitudes. This demonstrates the fact that radiosonde observations cannot necessarily be assumed to be representative of the atmosphere above the launch site.

Mobile robot tipover is a concern as it can create dangerous situations for operators and bystanders, cause collateral damage to the surrounding environment, and result in an aborted mission. Algorithms have been developed by others to assess the stability of the robot, and many of these algorithms have been demonstrated using simulated data. In order to verify that these algorithms accurately match real-world behavior, we have collected data of a mobile robot tipping over and then compared this data to the stability measures provided by three algorithms: Zero-Moment Point (ZMP), Force-Angle stability measure (FA), and Moment-Height Stability measure (MHS). A small mobile robot platform based on the iRobot PackBot drove a course including ramps and obstacles; an IMU and GPS provided inertial and positional data for the algorithms, and the actual tipover event is determined from video footage of the tests. The average normalized measure at tipover event initiation was found to be 0.665 for ZMP, -0.094 for FA, and 0.023 for MHS, where a value of 1 corresponds to resting stability. Standard deviations were 0.38, 0.84, and 0.67, respectively. The measures show a significant amount of noise, which is likely due to the vibrations caused by movement of the tracks and could be reduced by employing additional filtering during data collection. The preliminary real-world data validates these tipover algorithms as able to assess robot stability, and they can be used as part of a tipover avoidance system.

The signature of mid‐latitude convection observed by a 46.5 MHz wind‐profiling radar at Aberystwyth, UK (52.4°N, 4.0°W), is demonstrated by way of a case study. A key feature of such radars is their ability to measure the vertical air velocity directly, even under conditions of precipitation. Higher frequency radars, which have more typically been used for such studies, measure the net effect of hydrometeor terminal velocities and the air motion under such conditions. The radar is capable of observing both updrafts and downdrafts, with peak updrafts of the order of 10 m s−1. The signature of convection additionally consists of enhanced values of the radar return spectral width, which cannot be interpreted in terms of turbulence intensity, and reduced reliability of the corresponding radar‐derived horizontal wind components. When convection reaches the uppermost troposphere, the radar return signal power can be anomalously large leading to the radar‐derived tropopause altitude being overestimated. The presence of convection is confirmed by thermal infrared satellite imagery of high‐topped clouds. Use is also made of radiosonde and UHF wind‐profiler data.

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