Ray McGrath

Impact of Balloon Drift Errors in Radiosonde Data on Climate Statistics

Abstract Radiosonde data are a valuable resource in the detection of climate change in the upper atmosphere. Long time series of stratospheric temperature data, carefully screened and corrected to remove errors, are available for this purpose. Normal reporting practice usually ascribes a fixed time and position (the station location) to all data reported in the ascent. In reality, the ascent may take around 90 min to complete and the spatial drift of the radiosonde may exceed 200 km. This note examines the magnitude of the errors associated with this practice using simulated radiosonde data generated from the ECMWF reanalysis archive. The results suggest that the temperature errors, while generally small in the troposphere, are locally significant in the stratosphere, particularly in the jet stream areas. However, the impact of the drift errors on global climate statistics is very small. Errors in the wind and humidity data are also examined.

Boundary Filter Initialization of the Hirlam Model

In this paper we establish the mathematical framework for the filtering problem on a bounded interval, and provide a motivation for the use of the “half-sinc” function as a boundary filter. A boundary filter is one which yields output valid at the start or end of the interval on which the input is available. Such filters have obvious relevance to the problem of initialization for Numerical Weather Prediction. We also discuss some fundamental difficulties encountered when filtering time-limited functions.