The role of latent heating in warm frontogenesis

Igel, Adele L.; Heever, Susan C. van den

doi:10.1002/qj.2118

Cited by 19 publications

(10 citation statements)

References 30 publications

(37 reference statements)

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“…Davis and Emanuel, 1991;Stoelinga, 1996), thereby aiding in the intensification of these weather systems. Other microphysical processes including evaporation, melting, or sublimation of hydrometeors also have the potential to influence the frontal circulation (Huang and Emanuel, 1991;Szeto and Stewart, 1997;Igel and v. d. Heever, 2014) and the development of extratropical cyclones (Joos and Wernli, 2012;Dearden et al, 2016;Hardy et al, 2017). Furthermore, turbulence (Tory and Reeder, 2005;Adamson et al, 2006) and air-surface interactions (Muir and Reeder, 2010) can also modify the structure and evolution of cyclones and their accompanying fronts.…”

Section: Introductionmentioning

confidence: 99%

Systematic assessment of the diabatic processes that modify low-level potential vorticity in extratropical cyclones

Attinger¹,

Spreitzer²,

Boettcher³

et al. 2021

Preprint

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Abstract. Diabatic processes significantly affect the development and structure of extratropical cyclones. Previous studies quantified the dynamical relevance of selected diabatic processes by studying their influence on potential vorticity (PV) in individual cyclones. However, a more general assessment of the relevance of all PV-modifying processes in a larger ensemble of cyclones is currently missing. Based on a series of twelve 35-day model simulations using the Integrated Forecasting System (IFS) of the European Centre for Medium-range Weather Forecasts (ECMWF), this study systematically quantifies the relevance of individual diabatic processes for the dynamics of 288 rapidly intensifying extratropical cyclones. To this end, PV tendencies associated with each parametrized process in the model are accumulated along 15 h backward trajectories. The investigation focuses on regions of high PV (≥ 1 PVU) along the cold front, warm front, and in the cyclone center, as well as of negative PV (≤ −0.1 PVU) along the cold and warm front in the lower troposphere. On average, the primary processes that modify PV during the 24 h period of most rapid cyclone intensification remain temporally consistent for all anomalies considered. However, a pronounced case-to-case variability is found when comparing the dominant processes across individual cyclones. Along the cold front, PV is primarily generated by condensation in half of the investigated cyclones. For the remaining cyclones, convection or long-wave radiative cooling become the dominant process depending on environmental conditions. Results are similar for both seasons, with a reduced role of convection for the generation of PV along the cold front in the warm season. Negative PV west of the cold front is produced by turbulent exchange of momentum and temperature as well as long-wave radiative heating. The relevance of long-wave radiative heating is reduced during summer. The positive PV anomaly at the warm front is predominantly generated by condensation in the cold season, whereas turbulent mixing becomes the prevalent process during the warm season. Convection only plays a minor role for the generation of PV at the warm front. Negative PV along the warm front is produced by long-wave radiative heating, turbulent temperature tendencies, or melting of snow in the cold season. Turbulent temperature tendencies become the dominant process decreasing PV at the warm front in the warm season, together with melting of snow and turbulent exchange of momentum. The positive PV anomaly in the cyclone center is primarily produced by condensation, with only few cyclones where PV production is mainly associated with turbulent mixing or convection. A composite analysis further reveals that PV anomalies generated by convection require a negative air-sea temperature difference in the warm sector of the cyclone, which promotes a heat flux directed into the atmosphere and destabilizes the boundary layer. These cyclones primarily occur over warm ocean currents in the cold season. On the other hand, cyclones that occur in a significantly colder environment are often associated with a positive air-sea temperature difference in the warm sector, leading to PV generation by long-wave radiative cooling. Finally, long-wave radiative heating due to a negative air-sea temperature difference in the cold sector can produce negative PV along the cold and warm front. The general agreement between accumulated PV tendencies and the net PV change along trajectories is good. Therefore, the approach used in this study yields valuable insight regarding the specific physical processes that modify low-level PV in rapidly deepening extratropical cyclones.

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Section: Introductionmentioning

confidence: 99%

Systematic assessment of the diabatic processes that modify low-level potential vorticity in extratropical cyclones

Attinger¹,

Spreitzer²,

Boettcher³

et al. 2021

Preprint

View full text Add to dashboard Cite

show abstract

“…The dynamics of extratropical weather systems are substantially affected by heating and cooling due to diabatic processes, such as cloud latent heat release and radiative transfer, as well as by turbulent mixing and friction. This applies from the mesoscale to the large scale, including fronts (e.g., Parker and Thorpe 1995;Lackmann 2002;Igel and van den Heever 2014), cyclones (e.g., Stoelinga 1996;Rossa et al 2000;Adamson et al 2006), and Rossby waves (e.g., Grams et al 2011;Joos and Forbes 2016). Diagnosing and quantifying the systematic effects of diabatic processes on the dynamics is subject to ongoing research (e.g., Hardy et al 2017;Büeler and Pfahl 2017;Crezee et al 2017;Saffin et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Modification of Potential Vorticity near the Tropopause by Nonconservative Processes in the ECMWF Model

Spreitzer

Attinger

Boettcher

et al. 2019

Journal of the Atmospheric Sciences

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The upper-level potential vorticity (PV) structure plays a key role in the evolution of extratropical weather systems. PV is modified by nonconservative processes, such as cloud latent heating, radiative transfer, and turbulence. Using a Lagrangian method, material PV modification near the tropopause is attributed to specific parameterized processes in the global model of the European Centre for Medium-Range Weather Forecasts (ECMWF). In a case study, several flow features identified in a vertical section across an extratropical cyclone experienced strong PV modification. In particular clear-air turbulence at the jet stream is found to be a relevant process (i) for the PV structure of an upper-level front–jet system, corroborating previous observation-based findings of turbulent PV generation; (ii) for the purely turbulent decay of a tropopause fold, identified as an effective process of stratosphere–troposphere exchange; and (iii) in the ridge, where the Lagrangian accumulated turbulent PV modification exhibits a distinct vertical pattern, potentially impacting the strength of the tropopause inversion layer. In contrast, cloud processes affect the near-tropopause PV structure above a warm conveyor belt outflow in the ridge and above cold-sector convection. In agreement with previous studies, radiative PV production dominates in regions with an anomalously low tropopause, where both radiation and convection act to increase the vertical PV gradient across the tropopause. The particular strengths of the Lagrangian diagnostic are that it connects prominent tropopause structures with nonconservative PV modification along the flow and that it quantifies the relative importance of turbulence, radiation, and cloud processes for these modifications.

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“…Smagorinsky, ; Aubert, ; Danard, ; Kuo et al . ; Igel and van den Heever, ). Additionally, it was shown that other microphysical processes such as snow deposition, melting or sublimation and their exact formulation can also substantially influence the mesoscale details, track, and strength of extratropical cyclones (e.g.…”

Section: Introductionmentioning

confidence: 99%

Quantifying the role of individual diabatic processes for the formation of PV anomalies in a North Pacific cyclone

Attinger

Spreitzer

Boettcher

et al. 2019

Quart J Royal Meteoro Soc

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Processes that do not conserve potential vorticity (PV) have a profound impact on the intensity, evolution, and mesoscale details of extratropical weather systems. This study aims at quantifying and improving the understanding of how and when physical processes modify PV in cyclones. To this end, a 6-day forecast of a North Pacific cyclone is performed using a recent operational version of the ECMWF global numerical weather prediction model. Hourly instantaneous temperature and momentum tendencies of each parametrized process are used to compute the corresponding PV tendencies. By integrating these diabatic PV rates along backward trajectories, the relative contribution of individual processes for the PV budget can be assessed. The cold front is characterized by an elongated filament of increased PV, generated by latent heating due to condensation at the front as well as long-wave radiative cooling at the surface. Turbulent mixing at the interface of the boundary layer decreases PV behind the cold front during the early stage of the cyclone, while sublimation of snow produces negative PV in the mature phase. A broad region of enhanced PV is found along the warm front, generated by condensation and turbulence at the front as well as long-wave radiative cooling at the surface. The region of decreased PV north of the warm front is mainly modified by snow melting and sublimation. Finally, high values of PV along the bent-back front and the cyclone centre are generated by condensation, convection, snow melting and sublimation. In general, turbulent mixing offsets intense PV modification induced by the other processes. This study highlights the relevance of condensation, melting and sublimation of snow, long-wave radiative cooling, turbulence, and convection for the production of low-level PV anomalies and underlines the importance of correctly representing these processes in weather prediction models. K E Y W O R D Sconvection, diabatic processes, extratropical cyclone, IFS, microphysics, potential vorticity, radiation, turbulence Q J R Meteorol Soc. 2019;145:2454-2476.wileyonlinelibrary.com/journal/qj

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The role of latent heating in warm frontogenesis

Cited by 19 publications

References 30 publications

Systematic assessment of the diabatic processes that modify low-level potential vorticity in extratropical cyclones

Systematic assessment of the diabatic processes that modify low-level potential vorticity in extratropical cyclones

Modification of Potential Vorticity near the Tropopause by Nonconservative Processes in the ECMWF Model

Quantifying the role of individual diabatic processes for the formation of PV anomalies in a North Pacific cyclone

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