The diurnal path to persistent convective self-aggregation

Jensen, Gorm; Fiévet, Romain; Haerter, Jan O.

doi:10.1002/essoar.10508541.1

Cited by 3 publications

(6 citation statements)

References 43 publications

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“…In RCE, horizontal moisture variations were suggested to give rise to imbalances in thermal radiative emission, which would then drive a persistent circulation and resultant upstream moisture transport—reinforcing the initial moisture imbalance (Emanuel et al., 2014). Recent numerical work extends this notion to diurnal cycle simulations, where MCS emerge and cause abrupt transitions to such a moisture segregated state (Jensen et al., 2021). Importantly, the mesoscale convective system dynamics was found to occur only at sufficiently high horizontal model grid resolution, where CP interactions could be resolved sufficiently.…”

Section: Discussionmentioning

confidence: 96%

“…Cold pools have been implicated in a large range of cloud field properties, including the formation of MCS (Haerter et al., 2020; Houze Jr, 2004; Jensen et al., 2021; Kain & Fritsch, 1992; Schumacher & Rasmussen, 2020), the evolution of squall lines (M. D. Parker, 2008; D. J. Parker & Diop‐Kane, 2017; Rotunno et al., 1988; Weisman et al., 1988), the organization of trade‐wind cumuli (Dauhut et al., 2022; Seifert & Heus, 2013; Vogel et al., 2021; Zuidema et al., 2012) and stratocumuli (Glassmeier & Feingold, 2017), and idealized studies on convective self‐aggregation (Haerter, 2019; Haerter et al., 2019; Jeevanjee & Romps, 2013; Muller & Bony, 2015; Nissen & Haerter, 2021) and the convective diurnal cycle (Böing, 2016; Böing et al., 2012; Haerter et al., 2019; Haerter & Schlemmer, 2018; Schlemmer & Hohenegger, 2016). In all of these systems, the exact role of cold pools in giving structure to the cloud and precipitation fields is still not well‐understood.…”

Section: Discussionmentioning

confidence: 99%

“…As an extension of the current method, it could be interesting to devise a moisture tracking for simulated convective cloud fields. Especially for hysteretic phenomena, such as convective self‐aggregation, the long‐term memory of mesoscale moisture anomalies could play a critical role in maintaining a persistent atmospheric circulation (Bretherton et al., 2005; Jensen et al., 2021; Muller & Bony, 2015). In RCE, horizontal moisture variations were suggested to give rise to imbalances in thermal radiative emission, which would then drive a persistent circulation and resultant upstream moisture transport—reinforcing the initial moisture imbalance (Emanuel et al., 2014).…”

Section: Discussionmentioning

confidence: 99%

“…Besides the higher density compared to their surroundings, cold pools manifest themselves by a divergent near‐surface wind field and vortical structures along their “dynamical edges,” that is, the demarcation between the cold pool (CP) and the ambient atmosphere. Many recent studies have considered the characteristics of cold pools (Drager & van den Heever, 2017; Fournier & Haerter, 2019; Gentine et al., 2016; Henneberg et al., 2020; Schlemmer & Hohenegger, 2016; Torri & Kuang, 2019), because they have been implicated in the spatio‐temporal organization of the convective cloud field—thus impacting non‐random organization of rainfall, with consequences for extreme events, such as flooding (Böing, 2016; Haerter et al., 2019; Jensen et al., 2021; Schlemmer & Hohenegger, 2016; Simpson, 1980; Tompkins, 2001b).…”

Section: Introductionmentioning

confidence: 99%

“…Even the paradigmatic “convective self‐aggregation” (CSA), a system‐scale symmetry breaking, was found to be affected by CP activity (Haerter, 2019; Jeevanjee & Romps, 2013; Muller et al., 2022; Nissen & Haerter, 2021). In an effort to study more realistic configurations, recent numerical experiments employ temporally varying surface temperatures to investigate the impact of the diurnal cycle on correlated CP activity, especially regarding the formation of mesoscale convective systems (MCS) (Haerter et al., 2020; Jensen et al., 2021), stimulating conceptual models to help explain the complex processes involved (Niehues et al., 2021).…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Detecting Cold Pool Family Trees in Convection Resolving Simulations

Hoeller,

Fiévet,

Haerter

2024

J Adv Model Earth Syst

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Recent observations and modeling increasingly reveal the key role of cold pools in organizing the convective cloud field. Several methods for detecting cold pools in simulations exist, but are usually based on buoyancy fields and fall short of reliably identifying the active gust front. The current cold pool (CP) detection and tracking algorithm (CoolDeTA), aims to identify cold pools and follow them in time, thereby distinguishing their active gust fronts and the “offspring” rain cells generated nearby. To accomplish these tasks, CoolDeTA utilizes a combination of thermodynamic and dynamical variables and examines the spatial and temporal relationships between cold pools and rain events. We demonstrate that CoolDeTA can reconstruct CP family trees. Using CoolDeTA we can contrast radiative convective equilibrium (RCE) and diurnal cycle CP dynamics, as well as cases with vertical wind shear and without. We show that the results obtained are consistent with a conceptual model where CP triggering of children rain cells follows a simple birth rate, proportional to a CP's gust front length. The proportionality factor depends on the ambient atmospheric stability and is lower for RCE, in line with marginal stability as traditionally ascribed to the moist adiabat. In the diurnal case, where ambient stability is lower, the birth rate thus becomes substantially higher, in line with periodic insolation forcing—resulting in essentially run‐away mesoscale excitations generated by a single parent rain cell and its CP.

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Section: Discussionmentioning

confidence: 96%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Detecting Cold Pool Family Trees in Convection Resolving Simulations

Hoeller,

Fiévet,

Haerter

2024

J Adv Model Earth Syst

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U-Net Segmentation for the Detection of Convective Cold Pools From Cloud and Rainfall Fields

Hoeller

Fiévet²,

Haerter

2022

Preprint

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Convective cold pools (CPs) are known to mediate the interaction between convective rain cells and thereby help organize thunderstorm clusters, in particular mesoscale convective systems and extreme rainfall events. Unfortunately, the observational detection of CPs on a large scale has so far been hampered by the lack of relevant large-scale nearsurface data. Unlike numerical studies, where high-resolution near-surface fields of relevant quantities such as virtual temperature and winds are available and frequently used to detect cold pools, observational studies mainly identify CPs based on surface time series. Since research vessels or weather stations measure these time series locally, the characterization of cold pools from observations is limited to regional or station-based studies. To eventually enable studies on a global scale, we here develop and evaluate a methodology for the detection of CPs that relies only on data that (i) is globally available and (ii) has high spatio-temporal resolution. We trained convolutional neural networks to segment CPs in cloud and rainfall fields from high-resolution cloud resolving simulation output. Such data is not only available from simulations, but also from geostationary satellites that fulfill both (i) and (ii). The networks make use of a U-Net architecture, a common choice for image segmentation due to its strength in learning spatial correlations at different scales. Based on cloud and rainfall fields only, the trained networks systematically identify CP pixels in the simulation output. Our methodology may thus open for reliable global CP detection from space-borne sensors. As it also provides information on the spatial extent and the relative positioning of CPs over time, our method may offer new insight into the role of CPs in convective organization.

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Characteristics of Station‐Derived Convective Cold Pools Over Equatorial Africa

Hoeller,

Haerter,

Da Silva

2024

Geophysical Research Letters

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Due to their potential role in organizing tropical mesoscale convective systems, a better understanding of cold pool (CP) dynamics in such regions is critical, particularly over land where the diurnal cycle further concentrates convective activity. Numerical models help disentangle the processes involved but often lack observational benchmarks. To close this gap, we analyze nearly 43 years of five‐minute resolution near‐surface timeseries, recorded from 12 automatic weather stations across equatorial Africa during 2019–2023. We identify 4,218 CPs based on criteria for temperature and wind. The identified CP gust fronts, which exhibit respective median temperature and specific humidity decreases of 5.3 K and 2.8 g kg−1, closely correlate with satellite‐observed brightness temperature discontinuities. Despite weak diurnal variation in precipitation, observed CP occurrence shows a pronounced diurnal cycle with an afternoon peak — a feature we attribute to low‐level moisture conditions. Our findings can serve as observational benchmark to improve simulations of CP organization.

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The diurnal path to persistent convective self-aggregation

Cited by 3 publications

References 43 publications

Detecting Cold Pool Family Trees in Convection Resolving Simulations

Detecting Cold Pool Family Trees in Convection Resolving Simulations

U-Net Segmentation for the Detection of Convective Cold Pools From Cloud and Rainfall Fields

Characteristics of Station‐Derived Convective Cold Pools Over Equatorial Africa

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