The Life Cycles of Ice Crystals Detrained From the Tops of Deep Convection

Jensen, E. J.; Heever, Susan C. van den; Grant, Leah D.

doi:10.1029/2018jd028832

Cited by 25 publications

(35 citation statements)

References 38 publications

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“…Our main conclusions differ from a modeling study by Jensen et al (), in which they followed trajectories of ICs detrained from a midlatitude thunderstorm and simulated the first 3 hr of their microphysical evolution. Their results show the importance of gravitational settling and depositional growth.…”

Section: Discussioncontrasting

confidence: 99%

“…On the other hand, in the climatologically relevant RCE simulation, the cloud processes change the distribution of water vapor, which in turn drives a large part of the upper tropospheric cloud-scale circulation. Our main conclusions differ from a modeling study by Jensen et al (2018), in which they followed trajectories of ICs detrained from a midlatitude thunderstorm and simulated the first 3 hr of their microphysical evolution. Their results show the importance of gravitational settling and depositional growth.…”

Section: Drivers Of Anvil Evolutionsupporting

confidence: 91%

“…P3 is therefore well suited for studies of transitions of deep, precipitating anvils, to thin, nonprecipitating cirrus; a situation, in which we expect numerous transitions between several categories of atmospheric ice particles. In order to allow the formation of clouds with number concentrations of ICs comparable to those observed in freshly detrained anvil clouds (Heymsfield, Krämer, Luebke, et al, ; Jensen et al, ), we increased the upper limit of IC number concentration from 0.5 × 10 6 to 10 7 kg −1 (about 2–5 × 10 3 L −1 at the anvil cloud altitudes). Simulations of the dynamics of the MJO field campaign (Yoneyama et al, ) that used this increased upper limit on the IC number concentration showed good agreement with the observed radiative fluxes (Gasparini et al, ).…”

Section: Modeling Setupmentioning

confidence: 99%

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What Drives the Life Cycle of Tropical Anvil Clouds?

Gasparini

Blossey

Hartmann

et al. 2019

J Adv Model Earth Syst

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The net radiative effects of tropical clouds are determined by the evolution of thick, freshly detrained anvil clouds into thin anvil clouds. Thick anvil clouds reduce Earth's energy balance and cool the climate, while thin anvil clouds warm the climate. To determine role of these clouds in climate change we need to understand how interactions of their microphysical and macrophysical properties control their radiative properties. We explore anvil cloud evolution using a cloud‐resolving model in three‐simulation setups of increasing complexity to disentangle the impacts of the various components of diabatic heating and their interaction with cloud‐scale motions. The first phase of evolution and rapid cloud spreading is dominated by latent heating within convective updrafts. After the convective detrainment stops, most of the spreading and thinning of the anvil cloud is driven by cloud radiative processes and latent heating. The combination of radiative cooling at cloud top, latent cooling due to sublimation at cloud base, latent heating due to deposition and radiative heating in between leads to a sandwich‐like, cooling‐heating‐cooling structure. The heating sandwich promotes the development of two within‐anvil convective layers and a double cell circulation, dominated by strong outflow at 12‐km altitude with inflow above and below. Our study reveals how small‐scale processes including convective, microphysical processes, latent and radiative heating interact within the anvil cloud system. The absence or a different representation of only one component results in a significantly different cloud evolution with large impacts on cloud radiative effects.

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Section: Discussioncontrasting

confidence: 99%

Section: Drivers Of Anvil Evolutionsupporting

confidence: 91%

Section: Modeling Setupmentioning

confidence: 99%

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What Drives the Life Cycle of Tropical Anvil Clouds?

Gasparini

Blossey

Hartmann

et al. 2019

J Adv Model Earth Syst

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“…This factor‐of‐4 decrease in τ is accompanied by a relatively small decrease in geometric thickness, suggesting that optical thinning at the initial stages of the anvil life cycle is driven primarily by microphysical changes rather than geometric changes. This could reflect anvil precipitation and is consistent with previous findings that large ice crystals are removed relatively rapidly after detrainment (Garrett et al, 2005; Jensen et al, 2018). On the whole, these changes act to reduce the initial diurnal difference in microphysical structure, though the 01:30 anvils remain more top‐heavy in some respects at

τ = 10

.…”

Section: Resultssupporting

confidence: 91%

Tropical Anvil Clouds: Radiative Driving Toward a Preferred State

Sokol

Hartmann

2020

JGR Atmospheres

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The evolution of anvil clouds detrained from deep convective systems has important implications for the tropical energy balance and is thought to be shaped by radiative heating. We use combined radar-lidar observations and a radiative transfer model to investigate the influence of radiative heating on anvil cloud altitude, thickness, and microphysical structure. We find that high clouds with an optical depth between 1 and 2 are prevalent in tropical convective regions and can persist far from any convective source. These clouds are generally located at higher altitudes than optically thicker clouds, experience strong radiative heating, and contain high concentrations of ice crystals indicative of turbulence. These findings support the hypothesis that anvil clouds are driven toward and maintained at a preferred optical thickness that corresponds to a positive cloud radiative effect. Comparison of daytime and nighttime observations suggests that anvil thinning proceeds more rapidly at night, when net radiative cooling promotes the sinking of cloud top. It is hypothesized that the properties of aged anvil clouds and their susceptibility to radiative destabilization are shaped by the time of day at which the cloud was detrained. These results underscore the importance of small-scale processes in determining the radiative effect of tropical convection. Plain Language Summary Clouds play an important role in Earth's energy balance, especially in the tropics. Thick clouds cool the climate by reflecting sunlight, while thinner clouds located high in the atmosphere warm the climate due to their strong greenhouse effect. Tropical thunderstorms generate expansive cloud systems ("anvil" clouds) that initially exert a cooling effect but evolve over time to produce a warming effect. Their net impact on the climate system depends on how much time they spend in their cooling and warming stages. In this study, we use satellite measurements and a radiation model to examine how anvil clouds evolve. We find that anvil clouds with a climate-warming effect are pervasive in the tropics and can be found far from any thunderstorm that would have produced them, suggesting that they are maintained in their warming stage for long periods of time. We observe some unique characteristics of these clouds that provide clues about the processes that maintain them. Our findings provide real-world support for previous hypotheses that, until now, relied on computer simulations. They also highlight the importance of small-scale processes in shaping the large-scale tropical energy balance and underscore the need to consider these processes in projections of future climate change.

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“…Convectively detrained ice crystals are the largest as their ICNC has been reduced to account for aggregation in convective plumes (section 3.3.1.2). Ice crystal sizes above 100 μm have been observed in convective anvils (e.g., Jensen et al, 2009Jensen et al, , 2018; however, the detrained ice crystals are very large in the extra-tropics, which could partly explain the too low extra-tropical high-level cloud cover (Figure 7). When cloud droplets freeze, the resulting ice crystals initially have approximately the size of the droplets (Figure 9), but they will grow afterwards by depositional growth.…”

Section: 1029/2019ms001824mentioning

confidence: 99%

Developing a Cloud Scheme With Prognostic Cloud Fraction and Two Moment Microphysics for ECHAM‐HAM

Münch

Lohmann

2020

J Adv Model Earth Syst

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We present a new cloud scheme for the ECHAM‐HAM global climate model (GCM) that includes prognostic cloud fraction and allows for subsaturation and supersaturation with respect to ice separately in the cloud‐free and cloudy air. Stratiform clouds form by convective detrainment, turbulent vertical diffusion, and large‐scale ascent. For each process, the corresponding cloud fraction is calculated, and the individual updraft velocities are used to determine cloud droplet/ice crystal number concentrations. Further, convective condensate is always detrained as supercooled cloud droplets at mixed‐phase temperatures (between 235 and 273 K), and convectively detrained ice crystal number concentrations are calculated based on the updraft velocity. Finally, the new scheme explicitly calculates condensation/evaporation and deposition/sublimation rates for phase‐change calculations. The new cloud scheme simulates a reasonable present‐day climate, reduces the previously overestimated cirrus cloud fraction, and in general improves the simulation of ice clouds. The model simulates the observed in‐cloud supersaturation for cirrus clouds, and it allows for a better representation of the tropical to extra‐tropical ratio of the longwave cloud radiative effect. Further, the ice water path, the ice crystal number concentrations, and the supercooled liquid fractions in mixed‐phase clouds agree better with observations in the new model than in the reference model. Ice crystal formation is dominated by the liquid‐origin processes of convective detrainment and homogeneous freezing of cloud droplets. The simulated ice clouds strongly depend on model tuning choices, in particular, the enhancement of the aggregation rate of ice crystals.

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The Life Cycles of Ice Crystals Detrained From the Tops of Deep Convection

Cited by 25 publications

References 38 publications

What Drives the Life Cycle of Tropical Anvil Clouds?

What Drives the Life Cycle of Tropical Anvil Clouds?

Tropical Anvil Clouds: Radiative Driving Toward a Preferred State

Developing a Cloud Scheme With Prognostic Cloud Fraction and Two Moment Microphysics for ECHAM‐HAM

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