Sensitivity analysis of divergence and underlying processes around organised convection with a cloud resolving model

2020 ◽  
Author(s):  
Edward Groot ◽  
Holger Tost
Keyword(s):  
Heat Release ◽  
Latent Heat ◽  
Convective Cloud ◽  
Momentum Transport ◽  
Latent Heat Release ◽  
Moist Static Energy ◽  
Cloud Resolving Model ◽  
Convective Momentum Transport ◽  
Static Energy ◽  
The Impact

<p>In this study we are trying to understand (limits of) predictability related to (organised) convection and its upscale error growth.</p><p>For that purpose we aim to analyse the impact of three convection driving and amplifying processes, namely latent heat release, redistribution of moist static energy and convective momentum transport on the development of the convective cells. Furthermore, we plan to investigate uncertainties in these processes on downward propagation of the flow and ensemble spread.</p><p>The first results to be presented regard an idealised and strongly organised case of splitting convective storms modeled at different resolutions and with some small adaptations in the model convective cloud resolving model CM1. Currently processed resolution experiments show that both the actual divergence field and the processes supected to underlie it exhibit some sensitivity to model resolution on the subkilometre scale (100-1000 m). We can also show that the upper tropospheric divergence can be directly related to the latent heat release, as it is located vertically above the major latent heat releases. Nevertheless, neither the vertical redistribution of moist static energy nor the convective momentum transport are negligible and all three impact the divergent outflow of the convective storm.</p>

scholarly journals The Influence of Incipient Latent Heat Release on the Precipitation Distribution of the 24–25 January 2000 U.S. East Coast Cyclone

2005 ◽  
Vol 133 (7) ◽  
pp. 1913-1937 ◽  
Author(s):  
Michael J. Brennan ◽  
Gary M. Lackmann
Keyword(s):  
Heat Release ◽  
Latent Heat ◽  
Moisture Transport ◽  
East Coast ◽  
Weather Prediction ◽  
Lower Troposphere ◽  
Latent Heat Release ◽  
Precipitation Distribution ◽  
Balanced Flow ◽  
The Impact

Abstract The role of a diabatically produced lower-tropospheric potential vorticity (PV) maximum in determining the precipitation distribution of the 24–25 January 2000 U.S. East Coast cyclone is investigated. Operational numerical weather prediction (NWP) models performed poorly with this storm, even within 24 h of the event, as they were unable to properly forecast the westward extent of heavy precipitation over the Carolinas and mid-Atlantic. The development of an area of incipient precipitation (IP) around 0600 UTC 24 January over the southeastern United States prior to rapid cyclogenesis was also poorly forecasted by the operational NWP models. It is hypothesized that the lower-tropospheric diabatic PV maximum initially produced by the IP was important to subsequent inland moisture transport over the Carolinas and mid-Atlantic. A PV budget confirms that latent heat release in the midtroposphere associated with the IP led to the initial formation of a PV maximum in the lower troposphere that propagated eastward in association with the IP to the Atlantic coast late on 24 January. The impact of this PV maximum on the westward moisture transport was quantified by piecewise Ertel PV inversion. Results from the inversion show that the balanced flow associated with this evolving cyclonic PV maximum contributed substantially to the onshore moisture flux into the Carolinas and Virginia. The balanced flow associated with the PV anomaly also contributed to quasigeostrophic forcing for ascent in the region. These findings suggest that accurate numerical prediction of the precipitation distribution in this event requires adequate representation of the IP and its associated impacts on the PV distribution.

scholarly journals Potential-vorticity dynamics of troughs and ridges within Rossby wave packets during a 40-year reanalysis period

2021 ◽  
Vol 2 (3) ◽  
pp. 535-559
Author(s):  
Franziska Teubler ◽  
Michael Riemer
Keyword(s):  
Heat Release ◽  
Latent Heat ◽  
Rossby Wave ◽  
Potential Vorticity ◽  
Wave Packets ◽  
Radiative Cooling ◽  
Latent Heat Release ◽  
Divergent Flow ◽  
Moist Processes ◽  
The Impact

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 amplifications occur most prominently during the mature stage and towards the trailing edge of RWPs. Refining the pre-existing model, the maximum of divergent amplification occurs in advance of maximum 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, with the potential that this contribution is partly associated with cloud-radiative effects. 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-tropospheric 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, our results show 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. Consistent with theories of moist-baroclinic instability, both the amplitude and the relative location of latent heat release within the developing wave pattern depend on the state of the baroclinic development. Taking this “phasing” aspect into account, we provide some evidence that variability in the strength of divergent ridge amplification can predominantly be attributed to variability in latent heat release below rather than to secondary circulations associated with the dry dynamics of a baroclinic wave.

scholarly journals Impact of Assimilating Upper-Level Dropsonde Observations Collected during the TCI Field Campaign on the Prediction of Intensity and Structure of Hurricane Patricia (2015)

2019 ◽  
Vol 147 (8) ◽  
pp. 3069-3089 ◽  
Author(s):  
Jie Feng ◽  
Xuguang Wang
Keyword(s):  
Heat Release ◽  
Latent Heat ◽  
Inner Core ◽  
Motion Vector ◽  
Latent Heat Release ◽  
Field Campaign ◽  
Cyclone Intensity ◽  
Warm Core ◽  
Upper Level ◽  
The Impact

Abstract The dropsondes released during the Tropical Cyclone Intensity (TCI) field campaign provide high-resolution kinematic and thermodynamic measurements of tropical cyclones within the upper-level outflow and inner core. This study investigates the impact of these upper-level TCI dropsondes on analyses and prediction of Hurricane Patricia (2015) during its rapid intensification (RI) phase using an ensemble–variational data assimilation system. In the baseline experiment (BASE), both kinematic and thermodynamic observations of TCI dropsondes at all levels except the upper levels are assimilated. The upper-level wind and thermodynamic observations are assimilated in additional experiments to investigate their respective impacts. Compared to BASE, assimilating TCI upper-level wind observations improves the accuracy of outflow analyses verified against independent atmospheric motion vector (AMV) observations. It also strengthens the tangential and radial wind near the upper-level eyewall. The inertial stability within the upper-level eyewall is enhanced, and the maximum outflow is more aligned toward the inner core. Additionally, the analyses including the upper-level thermodynamic observations produce a warmer and drier core at high levels. Assimilating both upper-level kinematic and thermodynamic observations also improves the RI forecast. Compared to BASE, assimilating the upper-level wind induces more upright and inward-located eyewall convection, resulting in more latent heat release closer to the warm core. This process leads to stronger inner-core warming. Additionally, the initial warmer upper-level inner core produced by assimilating TCI thermodynamic observations also intensifies the convection and latent heat release within the eyewall, thus further contributing to the improved intensity forecasts.

scholarly journals Numerical Simulations of the Genesis of Typhoon Nuri (2008): Sensitivity to Initial Conditions and Implications for the Roles of Intense Convection and Moisture Conditions

2014 ◽  
Vol 29 (6) ◽  
pp. 1402-1424 ◽  
Author(s):  
Zhan Li ◽  
Zhaoxia Pu
Keyword(s):  
Numerical Simulations ◽  
Heat Release ◽  
Latent Heat ◽  
Initial Conditions ◽  
Deep Convection ◽  
Tropical Cyclone Genesis ◽  
Latent Heat Release ◽  
Numerical Predictions ◽  
Upper Level ◽  
The Impact

Abstract The sensitivity of numerical simulations of the genesis of Typhoon Nuri (2008) to initial conditions is examined using the Advanced Research core of the Weather Research and Forecasting (WRF) Model. The initial and boundary conditions are derived from two different global analyses at different lead times. One simulation successfully captures the processes of Nuri’s genesis and early intensification, whereas other simulations fail to predict the genesis of Nuri. Discrepancies between simulations with and without Nuri’s development are diagnosed. Significant differences are found in the development and organization of the intense convection during Nuri’s pregenesis phase. In the developing case, convection evolves and organizes into a “pouch” center of a westward-propagating wavelike disturbance. In the nondeveloping case, the convection fails to develop and organize. Favorable conditions for the development of deep convection include strong closed circulation patterns with high humidity, especially at the middle levels. An additional set of sensitivity experiments is performed to examine the impact of the moisture field on numerical simulations of Nuri’s genesis. Results confirm that the enhancement of mid- to upper-level moisture is favorable for Nuri’s genesis, mainly because moist conditions benefit deep convection, which produces diabatic heating from latent heat release when vertical airmass flux maxima occur in the mid- to upper-level atmosphere. The substantial warming at upper levels induced by latent heat release from persistent deep convection contributes to the drop in Nuri’s minimum central sea level pressure. Overall, results from this study demonstrate that it is essential to accurately represent the initial conditions in numerical predictions of tropical cyclone genesis.

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

2020 ◽  
Author(s):  
Franziska Teubler ◽  
Michael Riemer
Keyword(s):  
Life Cycle ◽  
Heat Release ◽  
Latent Heat ◽  
Rossby Wave ◽  
Potential Vorticity ◽  
Radiative Cooling ◽  
Latent Heat Release ◽  
Divergent Flow ◽  
Moist Processes ◽  
The Impact

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.

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

2021 ◽  
Author(s):  
Franziska Teubler ◽  
Michael Riemer
Keyword(s):  
Heat Release ◽  
Latent Heat ◽  
Rossby Wave ◽  
Potential Vorticity ◽  
Wave Packets ◽  
Radiative Cooling ◽  
Latent Heat Release ◽  
Divergent Flow ◽  
Moist Processes ◽  
The Impact

<p>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).</p><p> </p><p>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 maximum 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 only weakly 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 <em>moist</em>-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 to the jet (,phasing’).</p>

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