Linking rapid forecast error growth to diabatic processes

Sánchez, Claudio; Methven, John; Gray, Suzanne L.; Cullen, M. J. P.

doi:10.1002/qj.3861

Cited by 19 publications

(29 citation statements)

References 78 publications

(115 reference statements)

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“…While there is evidence that the impact of latent heat release is most prominently communicated to RWPs by uppertropospheric divergent outflow, it is in general difficult to accurately disentangle the relative contributions of dry and moist dynamics to upper-tropospheric divergence (e.g., Quinting and Jones, 2016;Sanchez et al, 2020), and thus its impact on RWPs. This study did not attempt such a quantitative decomposition, but a new qualitative hypothesis is provided for the interplay between dry and moist dynamics in RWPs.…”

Section: Discussionmentioning

confidence: 99%

“…Forecast errors grow most rapidly in regions of convection and precipitation (Hohenegger and Schär, 2007;Zhang et al, 2007;Selz and Craig, 2015). Moist processes in the warm sector of cyclones have been identified as one of the most important sources of forecast errors and uncertainty in the midlatitudes (Rodwell et al, 2018;Sanchez et al, 2020). Upper-tropospheric outflow most effectively communicates uncertainties associated with moist processes to the tropopause region , where these uncertainties have been shown to potentially transfer to the amplitude of the downstream ridge (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Potential-Vorticity Dynamics of Troughs and Ridges within Rossby Wave Packets during a 40-year reanalysis period

Teubler¹,

Riemer²

2020

Preprint

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Abstract. Rossby wave packets (RWPs) are fundamental to midlatitude dynamics and govern weather systems from their individual life cycles to their climatological distributions. Renewed interest in RWPs as precursors to high-impact weather events and in the context of atmospheric predictability motivates this study to revisit the dynamics of RWPs. A quantitative potential vorticity (PV) framework is employed. Based on the well established PV-thinking of midlatitude dynamics, the processes governing RWP amplitude evolution comprise group propagation of Rossby waves, baroclinic interaction, the impact of upper-tropospheric divergent flow, and direct diabatic PV modification by nonconservative processes. An advantage of the PV framework is that the impact of moist processes is more directly diagnosed than in alternative, established frameworks for RWP dynamics. The mean dynamics of more than 6000 RWPs from 1979–2017 are presented using ERA5 data, complemented with nonconservative tendencies from the Year of tropical convection data (available 2008–2010). Confirming a pre-existing model of RWP dynamics, group propagation within RWPs is consistent with linear barotropic theory, and baroclinic and divergent amplification occur most prominently during the mature stage and rather towards the trailing edge of RWPs. Refining the pre-existing model, the maximum of divergent amplification occurs in advance of max-imum baroclinic growth and baroclinic interaction tends to weaken RWP amplitude towards the leading edge. Downstream baroclinic development is confirmed to provide a valid description of RWP dynamics in both, summer and winter, although baroclinic growth is substantially smaller (about 50 %) in summer. Longwave radiative cooling makes a first-order contribution to ridge and trough amplitude. This large impact, however, is not coupled to other governing processes and is thus interpreted as a climatological background process. The direct impact of other nonconservative tendencies, including latent heat release, is an order of magnitude smaller than longwave radiative cooling. Arguably, latent heat release still has a substantial impact on RWPs by invigorating upper-troposhperic divergence. The divergent flow amplifies ridges and weakens troughs. This impact is of leading order and larger than that of baroclinic growth. To the extent that divergence is associated with latent heat release below, we argue that moist processes contribute to the well-known asymmetry in the spatial scale of troughs and ridges. For ridges, divergent amplification is strongly coupled to baroclinic growth and enhanced latent heat release. We thus propose that the life cycle of ridges is best described in terms of downstream moist-baroclinic development. Finally, our results demonstrate that divergent ridge amplification does not only depend on the magnitude of latent heat release but also on its relative location (phasing). We have demonstrated that phasing is a function of the stage of the baroclinic life cycle. We thus further hypothesize that phasing is the most relevant aspect of the dry baroclinic dynamics, rather than the impact of secondary circulations that develop associated with the dry dynamics of a baroclinically developing wave.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Potential-Vorticity Dynamics of Troughs and Ridges within Rossby Wave Packets during a 40-year reanalysis period

Teubler¹,

Riemer²

2020

Preprint

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“…Corridors of direct moisture advection from the mid-latitudes to the Arctic tend to ascend from the surface to the middle troposphere along moist isentropes (Laliberté and Kushner, 2014;Wernli and Papritz, 2018;Hao et al, 2021), andFeldl et al (2020) find that greater warming and moistening of the upper troposphere does not directly contribute to Arctic amplification as it does not affect the near-surface lapse rate feedback. However, transport of moist air masses from the mid-latitude near-surface layer to the Arctic middle and upper troposphere likely still contributes to Arctic warming indirectly, as latent heat release aids the formation of blocking anticyclones (Pfahl et al, 2015;Grams and Archambault, 2016;Zhang and Wang, 2018;Sánchez et al, 2020) that deflect cyclones poleward (Papritz and Dunn-Sigouin, 2020) and warm the lower troposphere through subsidence (Laliberté and Kushner, 2014;Ding et al, 2017;Wernli and Papritz, 2018;Papritz, 2020).…”

Section: Arctic Moisture Intrusions: Impacts On Sea Ice and Relationships With Blockingmentioning

confidence: 99%

Local and Remote Atmospheric Circulation Drivers of Arctic Change: A Review

et al. 2021

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Arctic Amplification is a fundamental feature of past, present, and modelled future climate. However, the causes of this “amplification” within Earth’s climate system are not fully understood. To date, warming in the Arctic has been most pronounced in autumn and winter seasons, with this trend predicted to continue based on model projections of future climate. Nevertheless, the mechanisms by which this will take place are numerous, interconnected. and complex. Will future Arctic Amplification be primarily driven by local, within-Arctic processes, or will external forces play a greater role in contributing to changing climate in this region? Motivated by this uncertainty in future Arctic climate, this review seeks to evaluate several of the key atmospheric circulation processes important to the ongoing discussion of Arctic amplification, focusing primarily on processes in the troposphere. Both local and remote drivers of Arctic amplification are considered, with specific focus given to high-latitude atmospheric blocking, poleward moisture transport, and tropical-high latitude subseasonal teleconnections. Impacts of circulation variability and moisture transport on sea ice, ice sheet surface mass balance, snow cover, and other surface cryospheric variables are reviewed and discussed. The future evolution of Arctic amplification is discussed in terms of projected future trends in atmospheric blocking and moisture transport and their coupling with the cryosphere. As high-latitude atmospheric circulation is strongly influenced by lower-latitude processes, the future state of tropical-to-Arctic teleconnections is also considered.

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“…Sánchez et al . (2020) have shown that in most NAWDEX intensive observing periods (IOPs) the ageostrophic horizontal wind attributable to the balanced (semi‐geostrophic) response to heating advects the tropopause on the western and northern flanks of ridges, resulting in ridge areal expansion. Therefore, here we focus on the IOPs where this behaviour has already been established, summarised in Table 1.…”

Section: Methodology Data and Modellingmentioning

confidence: 99%

“…Recently, Sánchez et al . (2020) have also shown that periods when diabatic influence on the horizontal advection of the tropopause, and associated ridge building across the North Atlantic, are stronger than normal are linked to lower predictability than usual for weather over Europe and “predictability barriers” where forecast error grows more rapidly than ensemble forecast spread. In other words, forecasts (at lead times greater than 2 days) are more uncertain when diabatic processes affect the tropopause location.…”

Section: Introductionmentioning

confidence: 99%

Circulation conservation in the outflow of warm conveyor belts and consequences for Rossby wave evolution

Saffin

Methven

Bland

et al. 2021

Quart J Royal Meteoro Soc

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Rossby waves on the jet stream are associated with meridional motions, displacing air and the strong potential vorticity (PV) gradient on isentropic surfaces. Poleward motion along sloping isentropic surfaces typically results in ascent and a ridge of air with low PV values. Latent heating in the ascending warm conveyor belt (WCB) enables air to cross isentropic surfaces so that the WCB outflow into a ridge occurs in a higher isentropic layer than the inflow. However, the PV impermeability theorem states that there can be no PV flux across isentropic surfaces, so how can heating alter the PV pattern of a Rossby wave? Here, the ways in which heating in WCBs can influence Rossby wave evolution at tropopause level are explained in the context of the PV impermeability theorem. First, a WCB outflow volume is defined by the upper tropospheric air in a ridge that has experienced net heating over the last few days, using a tracer within short global model forecasts. Second, the boundary of this outflow volume is tracked backwards using isentropic trajectories allowing quantification of the degree to which circulation is conserved, as predicted by theory, even though the WCB transports mass into the volume from lower isentropic layers. This diabatic flux of mass into the outflow volume results in an increase in density and expansion in the outflow area, the partition being determined approximately by PV inversion. The area expansion, combined with conservation of circulation, implies stronger anticyclonic vorticity. The relative vorticity change from divergent outflow can be as large as the decrease relative to the background planetary vorticity associated with poleward displacement of the circuit. The additional anticyclonic relative motion results in enhanced anticyclonic overturning of PV contours on the eastern flank of the ridge, altering qualitatively the nonlinear evolution of the Rossby wave.

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Linking rapid forecast error growth to diabatic processes

Cited by 19 publications

References 78 publications

Potential-Vorticity Dynamics of Troughs and Ridges within Rossby Wave Packets during a 40-year reanalysis period

Potential-Vorticity Dynamics of Troughs and Ridges within Rossby Wave Packets during a 40-year reanalysis period

Local and Remote Atmospheric Circulation Drivers of Arctic Change: A Review

Circulation conservation in the outflow of warm conveyor belts and consequences for Rossby wave evolution

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