Diagnosing the Horizontal Propagation of Rossby Wave Packets along the Midlatitude Waveguide

Abstract

It has been suggested that upper-tropospheric Rossby wave packets propagating along the midlatitude waveguide may play a role for triggering severe weather. This motivates the search for robust methods to detect and track Rossby wave packets and to diagnose their properties. In the framework of several observed cases, this paper compares different methods that have been proposed for these tasks, with an emphasis on horizontal propagation and on a particular formulation of a wave activity flux previously suggested by Takaya and Nakamura. The utility of this flux is compromised by the semigeostrophic nature of upper-tropospheric Rossby waves, but this problem can partly be overcome by a semigeostrophic coordinate transformation. The wave activity flux allows one to obtain information from a single snapshot about the meridional propagation, in particular propagation from or into polar and subtropical latitudes, as well as about the onset of wave breaking. This helps to clarify the dynamics of individual wave packets in cases where other, more conventional methods provide ambiguous or even misleading information. In some cases, the “true dynamics” of the Rossby wave packet turns out to be more complex than apparent from the more conventional diagnostics, and this may have important implications for the predictability of the wave packet.

New insights into Rossby wave packet properties in the extratropical UTLS using GNSS radio occultations

“…6). Although the parameter used by Wolf and Wirth (2017) is 300 hPa meridional winds and the time filtering is slightly different (30 day highpass), their spectrum also shows the two relative maxima of wave activity: one at mid-latitudes around w6 and the other at polar 25 latitudes and lower wavenumbers, similarly to our Fig. 3a.…”

“…Some methods make use of a threshold relative to the zonally averaged RWP envelope amplitude (e.g., Glatt and Wirth, 2014;Grazzini and Vitart, 2015;Quinting and Vitart, 2019). While solving the issue of pressure level distance to the tropopause, in 15 this case an even bigger problem arises: the presence of stronger wave activity over a near-global longitude range would increase the threshold substantially, reducing the diagnosed RWP size (Wolf and Wirth, 2017). Also, in the case of a zonally localized RWP growing into a high-amplitude and global wave due to resonant conditions (e.g., Petoukhov et al, 2013), a relative threshold would on the contrary yield a shrinking RWP.…”

Quasi‐stationary waves and their impact on European weather and extreme events

“…For this envelope reconstruction, we use the method of Zimin et al. (), but instead of using a fixed wavenumber range, we choose a latitude‐dependent wavenumber range (as in (Wolf and Wirth, )). The latitude dependence is based on the cosine decay of the main contribution of the power spectra of v ′ .…”

“…With v ′ ( ) given and assuming C consists of a specific range of relevant wavenumbers (typically s 1 ≈ 4 to s 2 ≈ 8 in midlatitudes), we can calculate the envelope of the wave A. For this envelope reconstruction, we use the method of Zimin et al (2003), but instead of using a fixed wavenumber range, we choose a latitude-dependent wavenumber range (as in Wolf and Wirth, 2017). The latitude dependence is based on the cosine decay of the main contribution of the power spectra of v ′ .…”

Climatic features of summertime baroclinic wave packets over Eurasia and the associated possible impacts on precipitation in southern China

“…In fact, the RWPs play a crucial role in weather system development in downstream region. Since the pioneering works by Yeh in 1949, and by Pedlosky in 1972(Pedlosky, 1972, many studies have investigated features of the RWP including its spatial structure and propagation (e.g., Martius et al, 2008;Torn and Hakim, 2015;Wolf and Wirth, 2017). RWPs are potential vorticity-related and under influences of waveguide and storm-track (Chang, 1999;Martius et al, 2010;Chang et al, 2002;Hakim, 2003;Grazzini and Vitart, 2014).…”