Low-Level Circulation and Its Coupling with Free-Tropospheric Variability as a Mechanism of Spontaneous Aggregation of Moist Convection

Yanase, Tomoro; Nishizawa, Seiya; Miura, Hiroaki; Takemi, Tetsuya; Tomita, Hirofumi

doi:10.1175/jas-d-21-0313.1

Cited by 3 publications

(14 citation statements)

References 61 publications

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“…This is consistent with previous findings by Yanase et al. (2022). Following the work by Tompkins and Semie (2017), we suggest that the free‐tropospheric drying and the associated radiative subsidence are strictly dependent on lateral mixing and updraft dilution.…”

Section: Resultssupporting

confidence: 94%

“…In particular, we argue that the radiative feedback loop which is responsible for the initial formation and the expansion of dry patches in the very initial stages, is initiated through updraft dilution in a dry environment instead of the radiative subsidence due to the WTG. This is consistent with previous findings by Yanase et al (2022). Following the work by Tompkins and Semie (2017), we suggest that the free-tropospheric drying and the associated radiative subsidence are strictly dependent on lateral mixing and updraft dilution.…”

Section: Triggering Mechanism Of Csasupporting

confidence: 93%

“…This factor is already present in the early stages of the simulation as shown in Figure 3b even if the different models starts with different temperature and different lower tropospheric relative humidity profiles. The initial drying of the free troposphere is essential for CSA (Shamekh et al., 2020; B. Yang & Tan, 2020; Yanase et al., 2022), since it allows a more efficient radiative cooling of the boundary layer in the dry regions and the onset of a shallow circulation that transports MSE from dry to moist regions (upgradient), contributing positively to CSA. This drying has to be caused by a relatively fast and efficient process which is acting on the triggering phase of CSA, which is considered here to occur during the first 5 days.…”

Section: Resultsmentioning

confidence: 99%

“…Thus, the representation of small-scale mixing processes becomes fundamental for establishing free-tropospheric (FT) drying, which is considered a prerequisite for the onset of CSA (B. Yang & Tan, 2020;Shamekh et al, 2020;Yanase et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

“…We also show how such perturbation varies with different horizontal grid sizes and how it can explain the sensitivity of CSA to horizontal resolution, independent of the amount of low‐level cloud. Thus, the representation of small‐scale mixing processes becomes fundamental for establishing free‐tropospheric (FT) drying, which is considered a prerequisite for the onset of CSA (B. Yang & Tan, 2020; Shamekh et al., 2020; Yanase et al., 2022).…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Numerical Diffusion and Turbulent Mixing in Convective Self‐Aggregation

Silvestri,

Saraceni,

Bongioannini Cerlini

2024

J Adv Model Earth Syst

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Convective Self‐Aggregation (CSA) is a common feature of idealized numerical simulations of the tropical atmosphere in Radiative‐Convective Equilibrium (RCE). However, at coarse grid resolution where deep convection is not fully resolved, the occurrence of this phenomenon is extremely sensitive to subgrid‐scale processes. This study examines the role of mixing and entrainment, provided by the turbulence model and the implicit numerical diffusion. The study compares the results of two models, WRF and SAM, by varying turbulence models, initial conditions, and horizontal spatial resolution. At a coarse grid resolution of 3 km, the removal of turbulent mixing prevents CSA in models with low numerical diffusivity but is preserved in models with high numerical diffusivity. When the horizontal grid resolution is refined to 1 km, CSA can only be achieved by increasing explicit turbulent mixing, even with a small amount of shallow clouds. Therefore, the sensitivity of CSA to horizontal grid resolution is not primarily caused by the decrease in shallow clouds. The analysis of the total water path spectrum suggests that the amplitude of initial humidity perturbations introduced by convection in the free troposphere is the key factor. This amplitude is regulated by turbulent mixing and diffusion at small scales. Prior to the onset of CSA, increased mixing makes updrafts more sensitive to the dryness of the free troposphere, which strengthens the moisture‐convection feedback. This leads to an increased distance between convective cores and a stronger humidity perturbation in the free troposphere, which can destabilize the RCE state.

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Section: Resultssupporting

confidence: 94%

Section: Triggering Mechanism Of Csasupporting

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Numerical Diffusion and Turbulent Mixing in Convective Self‐Aggregation

Silvestri,

Saraceni,

Bongioannini Cerlini

2024

J Adv Model Earth Syst

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The Unreasonable Efficiency of Total Rain Evaporation Removal in Triggering Convective Self‐Aggregation

Hwong,

Muller

2024

Geophysical Research Letters

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The elimination of rain evaporation in the planetary boundary layer (PBL) has been found to lead to convective self‐aggregation (CSA) even without radiative feedback, but the precise mechanisms underlying this phenomenon remain unclear. We conducted cloud‐resolving simulations with two domain sizes and progressively reduced rain evaporation in the PBL. Surprisingly, CSA only occurred when rain evaporation was almost completely removed. The additional convective heating resulting from the reduction of evaporative cooling in the moist patch was found to be the trigger, thereafter a dry subsidence intrusion into the PBL in the dry patch takes over and sets CSA in motion. Temperature and moisture anomalies oppose each other in their buoyancy effects, hence explaining the need for almost total rain evaporation removal. We also found radiative cooling and not cold pools to be the leading cause for the comparative ease of CSA to take place in the larger domain.

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