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  • Author or Editor: J. M. Rees x
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J. C. W. Denholm-Price
and
J. M. Rees

Abstract

The method of frequency-wavenumber “beamsteering” is a familiar tool in seismic applications and radar work where it is commonly used to detect coherent, propagating disturbances in “noisy” data. However, its use in meteorological situations is not well documented. In this paper the beamsteering method is summarized and its application in a meteorological context is discussed. Three different algorithms are used to detect single waves in artificial data with varying signal-to-noise ratios. Two of these are different beamsteering algorithms:one is a low-resolution scheme where the frequency-wavenumber spectrum is estimated using a fixed wavenumber window and the other a high-resolution method where the wavenumber window is effectively optimized for each wavenumber. These are compared with a method based on the cross-correlation function, which is more routinely used in meteorological studies. The results from this analysis provide a quantifiable measure of the performance and reliability of the three methods when detecting single waves at a given frequency. The performance of the high-resolution beamsteering algorithm is then tested in a similar manner with two waves at the same frequency.

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Gareth J. Marshall
,
Rebecca M. Vignols
, and
W. G. Rees

Abstract

The authors provide a detailed climatology and evaluation of recent climate change in the Kola Peninsula, Arctic Russia, a region influenced by both the North Atlantic and Arctic Oceans. The analysis is based on 50 years of monthly surface air temperature (SAT), precipitation (PPN), and sea level pressure (SLP) data from 10 meteorological stations for 1966–2015. Regional mean annual SAT is ~0°C: the moderating effect of the ocean is such that coastal (inland) stations have a positive (negative) value. Examined mean annual PPN totals rise from ~430 mm in the northeast of the region to ~600 mm in the west. Annual SAT in the Kola Peninsula has increased by 2.3° ± 1.0°C over the past 50 years. Seasonally, statistically significant warming has taken place in spring and fall, although the largest trend has occurred in winter. Although there has been no significant change in annual PPN, spring has become significantly wetter and fall drier. The former is associated with the only significant seasonal SLP trend (decrease). A positive winter North Atlantic Oscillation (NAO) index is generally associated with a warmer and wetter Kola Peninsula whereas a positive Siberian high (SH) index has the opposite impact. The relationship between both the NAO and SH and the SAT is broadly coherent across the region whereas their relationship with PPN varies markedly, although none of the relationships is temporally invariant. Reduced sea ice in the Barents and White Seas and associated circulation changes are likely to be the principal drivers behind the observed changes.

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J. M. Rees
,
J. C. W. Denholm-Price
,
J. C. King
, and
P. S. Anderson

Abstract

Internal gravity waves are frequently observed in stably stratified regions of the atmospheric boundary layer. In order to determine the statistical influence of such waves on the dynamics of the boundary layer it is necessary to compile information concerning properties of the waves such as frequency of occurrence, propagation, and spectral characteristics. Gravity wave climatologies have been compiled from relatively few locations. In this paper a climatological study of gravity waves, in the period range 1–20 min, propagating in the stably stratified atmospheric boundary layer overlying an Antarctic ice shelf is presented. An extensive set of boundary layer measurements were compiled throughout 1991. Surface pressure fluctuations were recorded from a spatial array of six sensitive microbarographs. Wind and temperature records from an instrumented mast were also available. A beam-steering technique has been used to determine wave parameters from the surface pressure data. The microbarographs detected the presence of internal gravity waves throughout the observational campaign. Root-mean-square pressure values were typically in the region 16–40 μb, but a significant number of isolated events with amplitudes of up to 180 μb were also found. Wave properties have been studied in conjunction with the mean wind and temperature profiles in the boundary layer. It was found that most of the wave activity did not originate locally, but from shear layers aloft, or, more commonly, from the katabatic flow regime where the ice shelf joins the Antarctic continent.

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