The 16-day planetary waves: multi-MF radar observations from the arctic to equator and comparisons with the HRDI measurements and the GSWM modelling results

Abstract

Abstract. The mesospheric and lower thermospheric (MLT) winds (60–100 km) obtained by multiple MF radars, located from the arctic to equator at Tromsø (70° N, 19° E), Saskatoon (52° N, 107° W), London (43° N, 81° W), Hawaii (21° N, 157° W) and Christmas Island (2° N, 157° W), respectively, are used to study the planetary-scale 16-day waves. Based on the simultaneous observations (1993/1994), the variabilities of the wave amplitudes, periods and phases are derived. At mid- and high-latitude locations the 16-day waves are usually pervasive in the winter-centred seasons (October through March), with the amplitude gradually decreasing with height. From the subtropical location to the equator, the summer wave activities become strong at some particular altitude where the inter-hemisphere wave ducts possibly allow for the leakage of the wave from the other hemispheric winter. The observational results are in good agreement with the theoretical conclusion that, for slowly westward-traveling waves, such as the 16-day wave, vertical propagation is permitted only in an eastward background flow of moderate speed which is present in the winter hemisphere. The wave period also varies with height and time in a range of about 12–24 days. The wave latitudinal differences and the vertical structures are compared with the Global Scale Wave Model (GSWM) for the winter situation. Although their amplitude variations and profiles have a similar tendency, the discrepancies are considerable. For example, the maximum zonal amplitude occurs around 40° N for radar but 30° N for the model. The phase differences between sites due to the latitudinal effect are basically consistent with the model prediction of equatorward phase-propagation. The global 16-day waves at 95 km from the HRDI wind measurements during 1992 through 1995 are also displayed. Again, the wave is a winter dominant phenomenon with strong amplitude around the 40–60° latitude-band on both hemispheres.Key words. Meteorology and atmospheric dynamics – waves and tides – middle atmosphere dynamics – thermospheric dynamics

Mean winds, temperatures and the 16- and 5-day planetary waves in the mesosphere and lower thermosphere over Bear Lake Observatory (42° N, 111° W)

“…There is also an oscillation of period ∼16 days and amplitudes of order ∼15 m s −1 and 10 K in December and January, similarly marked on the figure. These periods are consistent with those reported for the "5-day wave" and the "16-day wave", respectively (e.g., Espy and Witt, 1996;Espy et al, 1997;Luo et al, 2002b;Lieberman et al, 2003;Riggin et al, 2006;Day and Mitchell, 2010a,b;Day et al, 2011).…”

Longitudinal and latitudinal variations in dynamic characteristics of the MLT (70−95km): a study involving the CUJO network

“…The theoretical expectation for this wave is for propagation from the lower atmosphere and resulting activity throughout the winter hemisphere's eastward flow, with the possibility of summer mesopause activity due to propagation from the winter hemisphere. The results from the 2-D Global Scale Wave Model (GSWM) in Luo et al, (2000Luo et al, ( , 2002b were generally consistent with this simple scenario, but also demonstrated strong sensitivity to the background winds in the model. Our observations reinforce those conclusions: we again hypothesize that local conditions (winds, other PW modes, PW and GW interactions, and temperatures) may favour responses or resonances of different amplitude and at different periods at different sites.…”

Characteristics of Arctic winds at CANDAC-PEARL (80° N, 86° W) and Svalbard (78° N, 16° E) for 2006–2009: radar observations and comparisons with the model CMAM-DAS

“…For example, the observed zonal/EW wind's ∼10 d oscillation (taken to be the regional response to a Rossby PW) near day 30, is also evident in the NS component. The NS component is typically weaker in a Rossby wave (Luo et al, 2002). However, the feature in the contours near 10 d in the zonal-CMAM wavelet is less coherent and convincing, while it is not present in the meridional-wavelet.…”