Implications of Warm Rain in Shallow Cumulus and Congestus Clouds for Large-Scale Circulations

Nuijens, Louise; Emanuel, Kerry; Masunaga, Hirohiko; L’Ecuyer, Tristan

doi:10.1007/s10712-017-9429-z

Cited by 18 publications

(13 citation statements)

References 66 publications

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“…Over this area, at most 15% of all shallow cumulus cloud objects within a given grid box produce rain, while only 5%-10% of shallow cumulus cloud objects in all other regions produce rainfall. Nuijens et al (2017) found similar results, showing only 5%-10% of warm clouds produce rainfall globally. However, it should be noted that CloudSat only takes a snapshot of shallow convection at two times of the day.…”

Section: Resultsmentioning

confidence: 56%

“…These clouds impact both the atmospheric radiation budget (e.g., Zeng 2018) and the precipitation budget. As noted by Nuijens et al (2017), observations reveal 20%-40% of oceanic shallow cumulus clouds produce rain, although warm rain is usually light, with typical intensities less than 1 mm day 21 .…”

Section: Introductionmentioning

confidence: 85%

“…Most of the aforementioned studies are based on field campaign (e.g., Rauber et al 2007;Zhou et al 2015) or LES models (e.g., Nuijens et al 2017;Dagan et al 2018), which are limited to a small spatial domain for a short period. This limits the conditions over which clouds can be sampled and the effects of cloud size on precipitation can be examined.…”

Section: Introductionmentioning

confidence: 99%

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The Role of Cloud Size and Environmental Moisture in Shallow Cumulus Precipitation

Smalley

Rapp

2020

Journal of Applied Meteorology and Climatology

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Cloud models show that precipitation is more likely to occur in larger shallow clouds and/or in an environment with more moisture, in part as a result of decreasing the impacts of entrainment mixing on the updrafts. However, the role of cloud size in shallow cloud precipitation onset from global satellite observations has mostly been examined with precipitation proxies from imagers and has not been systematically examined in active sensors, primarily because of sensitivity limitations of previous spaceborne active instruments. Here we use the more sensitive CloudSat/CALIPSO observations to identify and characterize the properties of individual contiguous shallow cumulus cloud objects. The objects are conditionally sampled by cloud-top height to determine the changes in precipitation likelihood with increasing cloud size and column water vapor. On average, raining shallow cumulus clouds are typically taller by a factor of 2 and have a greater horizontal extent than their nonraining counterparts. Results show that for a fixed cloud-top height the likelihood of precipitation increases with increasing cloud size and generally follows a double power-law distribution. This suggests that the smallest cloud objects are able to grow freely within the boundary layer but the largest cloud objects are limited by environmental moisture. This is supported by our results showing that, for a fixed cloud-top height and cloud size, the precipitation likelihood also increases as environmental moisture increases. These results are consistent with the hypothesis that larger clouds occurring in a wetter environment may be better able to protect their updrafts from entrainment effects, increasing their chances of raining.

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Section: Resultsmentioning

confidence: 56%

Section: Introductionmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

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The Role of Cloud Size and Environmental Moisture in Shallow Cumulus Precipitation

Smalley

Rapp

2020

Journal of Applied Meteorology and Climatology

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“…3 and 4 are examples of isolated convection in the northeast Atlantic trade winds able to reach 4 km coexisting with cloud lines lacking precipitation. These images are representative of the northeast Atlantic (Zuidema et al 2012;Nuijens et al 2017). The (Zuidema et al 2016).…”

Section: Cold Pools From Convection Reaching the Mid-tropospherementioning

confidence: 99%

A Survey of Precipitation-Induced Atmospheric Cold Pools over Oceans and Their Interactions with the Larger-Scale Environment

et al. 2017

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Pools of air cooled by partial rain evaporation span up to several hundreds of kilometers in nature and typically last less than 1 day, ultimately losing their identity to the large-scale flow. These fundamentally differ in character from the radiatively-driven dry pools defining convective aggregation. Advancement in remote sensing and in computer capabilities has promoted exploration of how precipitation-induced cold pool processes modify the convective spectrum and life cycle. This contribution surveys current understanding of such cold pools over the tropical and subtropical oceans. In shallow convection with low rain rates, the cold pools moisten, preserving the near-surface equivalent potential temperature or increasing it if the surface moisture fluxes cannot ventilate beyond the new surface layer; both conditions indicate downdraft origin air from within the boundary layer. When rain rates exceed $ 2 mm h À1 , convective-scale downdrafts can bring down drier air of lower equivalent potential temperature from above the boundary layer. The resulting density currents facilitate the lifting of locally thermodynamically favorable air and can impose an arc-shaped mesoscale cloud organization. This organization allows clouds capable of reaching 4-5 km within otherwise dry environments. These are more commonly observed in the northern hemisphere trade wind regime, where the flow to the intertropical 123Surv Geophys (2017) 38:1283-1305 https://doi.org/10.1007/s10712-017-9447-x convergence zone is unimpeded by the equator. Their near-surface air properties share much with those shown from cold pools sampled in the equatorial Indian Ocean. Cold pools are most effective at influencing the mesoscale organization when the atmosphere is moist in the lower free troposphere and dry above, suggesting an optimal range of water vapor paths. Outstanding questions on the relationship between cold pools, their accompanying moisture distribution and cloud cover are detailed further. Near-surface water vapor rings are documented in one model inside but near the cold pool edge; these are not consistent with observations, but do improve with smaller horizontal grid spacings.

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“…These range bins with averaged reflectivity greater than 10 dBZ and averaged velocity lower than −3 m s −1 are identified as precipitation (Chandra et al, 2015). However, the drizzle with smaller sizes and lower velocity (Kollias et al, 2011;O'Connor et al, 2005) may not be identified by the above method. Thus, the radar echoes that below the lidar-detected cloud base, while still being connected to the cloud, are marked as drizzle (Wu et al, 2015;Yang et al, 2018) and removed from the training data.…”

Section: Removing Noise and Non-cloud Meteorological Targetmentioning

confidence: 99%

A robust low-level cloud and clutter discrimination method for ground-based millimeter-wavelength cloud radar

et al. 2021

Atmos. Meas. Tech.

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Abstract. Low-level clouds play a key role in the energy budget and hydrological cycle of the climate system. The accurate long-term observation of low-level clouds is essential for understanding their climate effect and model constraints. Both ground-based and spaceborne millimeter-wavelength cloud radars can penetrate clouds but the detected low-level clouds are always contaminated by clutter, which needs to be removed. In this study, we develop an algorithm to accurately separate low-level clouds from clutter for ground-based cloud radar using multi-dimensional probability distribution functions along with the Bayesian method. The radar reflectivity, linear depolarization ratio, spectral width, and their dependence on the time of the day, height, and season are used as the discriminants. A low-pass spatial filter is applied to the Bayesian undecided classification mask by considering the spatial correlation difference between clouds and clutter. The final feature mask result has a good agreement with lidar detection, showing a high probability of detection rate (98.45 %) and a low false alarm rate (0.37 %). This algorithm will be used to reliably detect low-level clouds at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) site for the study of their climate effect and the interaction with local abundant dust aerosol in semi-arid regions.

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Implications of Warm Rain in Shallow Cumulus and Congestus Clouds for Large-Scale Circulations

Cited by 18 publications

References 66 publications

The Role of Cloud Size and Environmental Moisture in Shallow Cumulus Precipitation

The Role of Cloud Size and Environmental Moisture in Shallow Cumulus Precipitation

A Survey of Precipitation-Induced Atmospheric Cold Pools over Oceans and Their Interactions with the Larger-Scale Environment

A robust low-level cloud and clutter discrimination method for ground-based millimeter-wavelength cloud radar

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