Zonal wave numbers of the summertime 2 day planetary wave observed in the mesosphere by EOS Aura Microwave Limb Sounder

Abstract

Recent observations and theoretical work suggest that the 2 day planetary wave in the summertime mesosphere is composed of multiple superposed zonal wave numbers. Here we use EOS Aura Microwave Limb Sounder (MLS) temperature data to determine the component zonal wave numbers of the 2 day wave in the mesosphere at latitudes of 70°S to 70°N from 2004 to 2009. We consider the effect of aliasing between different wave numbers and note that significant aliasing can occur and result in spurious signals, particularly at high latitudes in winter. The seasonal evolution of the different wave numbers is investigated and found to be very different between the Northern and Southern Hemispheres. In both hemispheres the wave is dominated by westward traveling waves of zonal wave number 3 and 4 (W3 and W4). However, in the Southern Hemisphere the wave is dominated by the W3 component, but in the Northern Hemisphere the W3 component is smaller and the W4 component is often of similar or larger amplitude. A small‐amplitude westward traveling zonal wave number 2 (W2) wave is also evident in both hemispheres. In the Northern Hemisphere, the W2 amplitudes never exceed 3 K, the W3 amplitudes can reach 3.5 K, and the W4 can be the largest component, reaching amplitudes of 4 K. In the Southern Hemisphere, the W2 amplitudes can reach up to 3.5 K, the W3 amplitudes can be much larger, reaching 12 K, and the W4 amplitudes are smaller than in the Northern Hemisphere, in 4 out of 5 years not exceeding 3 K. The Northern Hemisphere W4 can reach large amplitudes in August when the W3 is small, which means that the late summer Northern Hemisphere quasi‐2 day wave is usually a W4 oscillation rather than the familiar W3. In contrast, in the Southern Hemisphere, the W3 is often larger than the W4 around the summer solstice, and there are no episodes observed where the wave becomes dominated by the W4 for an extended period of time. A high degree of interannual variability is evident, particularly in the Southern Hemisphere, where the W3 peak amplitudes vary from 12 K in January 2006 to 3 K in January 2009. The height‐latitude structure of the W4 suggests that this wave is a (4, 0) Rossby‐gravity wave.

Global climatological variability of quasi-two-day waves revealed by TIMED/SABER observations

“…In order to better understand the generation mechanisms and propagation characteristics of QTDWs, global structure of QTDW amplitudes from stratosphere to the upper In the SH (NH), the maximum QTDW amplitude often occurs in January (July), which coincides with previous research (Pancheva et al, 2004;Tunbridge et al, 2011). Therefore, only amplitudes in these months are statistical analyzed.…”

“…The most prominent component in the MLT is the quasitwo-day wave (QTDW), which is able to affect horizontal wind and temperature in the middle atmosphere (Palo et al, 1999). Amplitudes of QTDWs in temperature and wind can reach 12 K (Tunbridge et al, 2011) and 60 m s −1 (Wu et al, 1993). Traces of QTDWs can also be found in atmospheric H 2 O, carbon monoxide, OH emission, and height of the F2 layer (Wu et al, 1993;Randel, 1994;Forbes and Zhang, 1997;Limpasuvan and Wu, 2003;Limpasuvan et al, 2005;Tunbridge et al, 2011;Pedatella and Forbes, 2012).…”

“…During summertime, the QTDW was proved to be the strongest PW in the MLT (Muller, 1972;Roger and Prata, 1981;Wu et al, 1993;Harris and Vincent, 1993;Harris, 1994;Garcia et al, 2005;Palo et al, 2007;McCormack et al, 2009), and thus it is taken as the primary topic of this paper. In addition, most of our attention is paid to the summertime in the altitude range from 70 to 90 km and from 30 • S (N) to 50 • S (N) in latitude, where intense QTDWs recur regularly (Muller, 1972;Muller and Nelson, 1978;Craig et al, 1980;Salby, 1981;Meek et al, 1996;Garcia et al, 2005;Tunbridge et al, 2011). On the satellite's yawing days, data points are extraordinarily scattered in latitude and unsuitable for spectral analysis.…”

“…Satellite observations contribute greatly to our knowledge of global morphology of QTDWs. Evident QTDWs often occur in the middle and upper atmosphere at mid-high latitudes after summer solstice (Rodger and Prata, 1981;Randel, 1994;Tunbridge et al, 2011), and amplitudes of them are twice larger in the SH than in the NH (Limpasuvan et al, 2000). Wavenumbers of distinctive QTDWs in the SH are usually −3, while in the NH they are −3 and −4 (Limpasu- van et al, 2000;Garcia et al, 2005).…”

“…Satellites can almost provide whole global wind fields, temperature and atmospheric compositions from the upper troposphere to the lower thermosphere. For example, the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) can measure the lower atmospheric temperature (He et al, 2009;Yang and Zou, 2012); the Upper Atmospheric Research Satellite/High Resolution Doppler Imager (UARS/HRDI) measures temperature, zonal and meridional wind, water vapor and ozone concentration in the middle and upper atmosphere (Wu et al, 1993(Wu et al, , 1996; the Thermosphere Ionosphere Mesosphere Energetics Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) is used for temperature measurements in the upper atmosphere (Xu et al, 2007a, b); and the line-of-sight (LOS) winds can be surveyed by the Microwave Limb Sounder (MLS) on Aura (Tunbridge et al, 2011). Satellite observations contribute greatly to our knowledge of global morphology of QTDWs.…”