Tropical Cirrus in Global Storm-Resolving Models. Part I: Role of Deep Convection

Nugent, Jacqueline M; Turbeville, Samantha M; Bretherton, Christopher S.; Blossey, Peter N.; Ackerman, Thomas P.

doi:10.1002/essoar.10507904.1

Cited by 3 publications

(2 citation statements)

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“…Following Sokol and Hartmann (2020), Nugent et al (2021), andTurbeville et al (2021), we use IWP to distinguish three different categories of ice clouds:…”

Section: Ice Cloud Classification Methodsmentioning

confidence: 99%

Stable water isotope signals in tropical ice clouds in the West African monsoon simulated with a regional convection-permitting model

Vries¹,

Aemisegger²,

Wernli³

2021

Preprint

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Abstract. Tropical ice clouds have an important influence on the Earth’s radiative balance. They often form as a result of tropical deep convection, which strongly affects the water budget of the tropical tropopause layer. Ice cloud formation involves complex interactions on various scales, which are not fully understood yet and lead to large uncertainties in climate predictions. In this study, we investigate the formation of tropical ice clouds related to deep convection in the West African monsoon, using stable water isotopes as tracers of moist atmospheric processes. We perform simulations using the regional isotope-enabled model COSMOiso with different resolutions and treatments of convection for the period of June–July 2016. First, we evaluate the ability of our simulations to represent the isotopic composition of monthly precipitation through comparison with GNIP observations, and the precipitation characteristics related to the monsoon evolution and convective storms based on insights from the DACCIWA field campaign in 2016. Next, a case study of a mesoscale convective system (MCS) explores the isotope signatures of tropical deep convection in atmospheric water vapour and ice. Convective updrafts within the MCS inject enriched ice into the upper troposphere leading to depletion of vapour within these updrafts due to the preferential condensation and deposition of heavy isotopes. Water vapour in downdrafts within the same MCS are enriched by non-fractionating sublimation of ice. In contrast to ice within the MCS core regions, ice in widespread cirrus shields is isotopically in approximate equilibrium with the ambient vapour, which is consistent with in situ formation of ice. These findings from the case study are supported by a statistical evaluation of isotope signals in the West African monsoon ice clouds. The following five key processes related to tropical ice clouds can be distinguished based on their characteristic isotope signatures: (1) convective lofting of enriched ice into the upper troposphere, (2) cirrus clouds that form in situ from ambient vapour under equilibrium fractionation, (3) sedimentation and sublimation of ice in the mixed-phase cloud layer in the vicinity of convective systems and underneath cirrus shields, (4) sublimation of ice in convective downdrafts that enriches the environmental vapour, and (5) the freezing of liquid water in the mixed-phase cloud layer at the base of convective updrafts. Importantly, the results show that convective systems strongly modulate the humidity budget and the isotopic composition of the lower tropical tropopause layer. They contribute to about 40 % of the total water and 60 % of HDO in the 175–125 hPa layer in the African monsoon region according to estimates based on our model simulations. Overall, this study demonstrates that isotopes can serve as useful tracers to disentangle the role of different processes in the Earth’s water cycle, including convective transport, the formation of ice clouds, and their impact on the tropical tropopause layer.

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“…Following Sokol and Hartmann (2020), Nugent et al (2021), andTurbeville et al (2021), we use IWP to distinguish three different categories of ice clouds:…”

Section: Ice Cloud Classification Methodsmentioning

confidence: 99%

Stable water isotope signals in tropical ice clouds in the West African monsoon simulated with a regional convection-permitting model

Vries¹,

Aemisegger²,

Wernli³

2021

Preprint

View full text Add to dashboard Cite

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“…While this new class of global models has been proven useful for understanding the properties of intense convection on a global scale (Cheng et al, 2022;Harris et al, 2023), these models are at best marginally able to accurately simulate individual supercells. In fact, this group of global models is referred to as global storm-resolving models in numerous studies (e.g., Judt et al, 2021;Nugent et al, 2022). Zarzycki et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Supercells and Tornado-like Vortices in an Idealized Global Atmosphere Model

Cheng,

Lin,

Harris

et al. 2023

Preprint

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We investigate the representation of individual supercells and intriguing tornado-like vortices in a simplified, locally-refined global atmosphere model. The model, featuring grid stretching, can locally enhance the model resolution and economically reach the cloud-resolving scale. Given an unstable sheared environment, the model can simulate supercells realistically, with a near-ground vortex and funnel cloud at the center of a rotating updraft reminiscent of a tornado. An analysis of the vorticity budget suggests that the updraft core of the supercell tilts environmental horizontal vorticity into the tornado-like vortex. The updraft also acts to amplify the vortex through vertical stretching. Results suggest that the simulated vortex is dynamically similar to observed tornadoes and modeling studies at much higher horizontal resolution.

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Opinion: Tropical cirrus – from micro-scale processes to climate-scale impacts

Gasparini,

Sullivan,

Sokol

et al. 2023

Atmos. Chem. Phys.

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Abstract. Tropical cirrus clouds, i.e., any type of ice cloud with tops above 400 hPa, play a critical role in the climate system and are a major source of uncertainty in our understanding of global warming. Tropical cirrus clouds involve processes spanning a wide range of spatial and temporal scales, from ice microphysics on cloud scales to mesoscale convective organization and planetary wave dynamics. This complexity makes tropical cirrus clouds notoriously difficult to model and has left many important questions stubbornly unanswered. At the same time, their multi-scale nature makes them well-positioned to benefit from the rise of global, high-resolution simulations of Earth's atmosphere and a growing abundance of remotely sensed and in situ observations. Rapid progress on our understanding of tropical cirrus requires coordinated efforts to take advantage of these modern computational and observational abilities. In this opinion paper, we review recent progress in cirrus studies, highlight important unanswered questions, and discuss promising paths forward. Significant progress has been made in understanding the life cycle of convectively generated “anvil” cirrus and the response of their macrophysical properties to large-scale controls. On the other hand, much work remains to be done to fully understand how small-scale anvil processes and the climatological anvil radiative effect will respond to global warming. Thin, in situ formed cirrus clouds are now known to be closely tied to the thermal structure and humidity of the tropical tropopause layer, but microphysical uncertainties prevent a full understanding of this link, as well as the precise amount of water vapor entering the stratosphere. Model representation of ice-nucleating particles, water vapor supersaturation, and ice depositional growth continue to pose great challenges to cirrus modeling. We believe that major advances in the understanding of tropical cirrus can be made through a combination of cross-tool synthesis and cross-scale studies conducted by cross-disciplinary research teams.

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Tropical Cirrus in Global Storm-Resolving Models. Part I: Role of Deep Convection

Cited by 3 publications

References 0 publications

Stable water isotope signals in tropical ice clouds in the West African monsoon simulated with a regional convection-permitting model

Stable water isotope signals in tropical ice clouds in the West African monsoon simulated with a regional convection-permitting model

Supercells and Tornado-like Vortices in an Idealized Global Atmosphere Model

Opinion: Tropical cirrus – from micro-scale processes to climate-scale impacts

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