Diurnal differences in tropical maritime anvil cloud evolution

2021 ◽  
pp. 1-66
Author(s):  
Adam B. Sokol ◽  
Casey J. Wall ◽  
Dennis L. Hartmann ◽  
Peter N. Blossey
Keyword(s):  
Diurnal Cycle ◽  
Deep Convection ◽  
Radiative Heating ◽  
Cloud Base ◽  
Diurnal Difference ◽  
Size Number ◽  
Cloud Resolving Model ◽  
Ice Crystal Size ◽  
Environmental Air ◽  
Cloud Evolution

Abstract Satellite observations of tropical maritime convection indicate an afternoon maximum in anvil cloud fraction that cannot be explained by the diurnal cycle of deep convection peaking at night. We use idealized cloud-resolving model simulations of single anvil cloud evolution pathways, initialized at different times of the day, to show that tropical anvil clouds formed during the day are more widespread and longer lasting than those formed at night. This diurnal difference is caused by shortwave radiative heating, which lofts and spreads anvil clouds via a mesoscale circulation that is largely absent at night, when a different, longwave-driven circulation dominates. The nighttime circulation entrains dry environmental air that erodes cloud top and shortens anvil lifetime. Increased ice nucleation in more turbulent nighttime conditions supported by the longwave cloud top cooling and cloud base heating dipole cannot overcompensate for the effect of diurnal shortwave radiative heating. Radiative-convective equilibrium simulations with a realistic diurnal cycle of insolation confirm the crucial role of shortwave heating in lofting and sustaining anvil clouds. The shortwave-driven mesoscale ascent leads to daytime anvils with larger ice crystal size, number concentration, and water content at cloud top than their nighttime counterparts.

Do Undiluted Convective Plumes Exist in the Upper Tropical Troposphere?

2010 ◽  
Vol 67 (2) ◽  
pp. 468-484 ◽  
Author(s):  
David M. Romps ◽  
Zhiming Kuang
Keyword(s):  
Kinetic Energy ◽  
Deep Convection ◽  
Potential Temperature ◽  
Specific Humidity ◽  
Heat Of Fusion ◽  
Cloud Base ◽  
Base Temperature ◽  
Neutral Buoyancy ◽  
Environmental Air ◽  
Ice Phase

Abstract Using a passive tracer, entrainment is studied in cloud-resolving simulations of deep convection in radiative–convective equilibrium. It is found that the convective flux of undiluted parcels decays with height exponentially, indicating a constant probability per vertical distance of mixing with environmental air. This probability per distance is sufficiently large that undiluted updrafts are negligible above a height of 4–5 km and virtually absent above 10 km. These results are shown to be independent of the horizontal grid size within the range of 3.2 km to 100 m. Plumes that do reach the tropopause are found to be highly diluted. An equivalent potential temperature is defined that is exactly conserved for all reversible adiabatic transformations, including those with ice. Using this conserved variable, it is shown that the latent heat of fusion (from both freezing and deposition) causes only a small increase in the level of neutral buoyancy near the tropopause. In fact, when taken to sufficiently low pressures, a parcel with an ice phase ends up colder than it would without an ice phase. Nevertheless, the contribution from fusion to a parcel’s kinetic energy is quite large. Using an ensemble of tracers, information is encoded in parcels at the cloud base and decoded where the parcel is observed in the free troposphere. Using this technique, clouds at the tropopause are diagnosed for their cloud-base temperature, specific humidity, and vertical velocity. Using these as the initial values for a Lagrangian parcel model, it is shown that fusion provides the kinetic energy required for diluted parcels to reach the tropopause.

scholarly journals A study of the effect of overshooting deep convection on the water content of the TTL and lower stratosphere from Cloud Resolving Model simulations

2007 ◽  
Vol 7 (18) ◽  
pp. 4977-5002 ◽  
Author(s):  
D. P. Grosvenor ◽  
T. W. Choularton ◽  
H. Coe ◽  
G. Held
Keyword(s):  
Boundary Layer ◽  
Water Content ◽  
Lower Stratosphere ◽  
Deep Convection ◽  
Cold Trap ◽  
Cloud Base ◽  
Anthropogenic Aerosols ◽  
Height Range ◽  
Cloud Resolving Model ◽  
The Impact

Abstract. Simulations of overshooting, tropical deep convection using a Cloud Resolving Model with bulk microphysics are presented in order to examine the effect on the water content of the TTL (Tropical Tropopause Layer) and lower stratosphere. This case study is a subproject of the HIBISCUS (Impact of tropical convection on the upper troposphere and lower stratosphere at global scale) campaign, which took place in Bauru, Brazil (22° S, 49° W), from the end of January to early March 2004. Comparisons between 2-D and 3-D simulations suggest that the use of 3-D dynamics is vital in order to capture the mixing between the overshoot and the stratospheric air, which caused evaporation of ice and resulted in an overall moistening of the lower stratosphere. In contrast, a dehydrating effect was predicted by the 2-D simulation due to the extra time, allowed by the lack of mixing, for the ice transported to the region to precipitate out of the overshoot air. Three different strengths of convection are simulated in 3-D by applying successively lower heating rates (used to initiate the convection) in the boundary layer. Moistening is produced in all cases, indicating that convective vigour is not a factor in whether moistening or dehydration is produced by clouds that penetrate the tropopause, since the weakest case only just did so. An estimate of the moistening effect of these clouds on an air parcel traversing a convective region is made based on the domain mean simulated moistening and the frequency of convective events observed by the IPMet (Instituto de Pesquisas Meteorológicas, Universidade Estadual Paulista) radar (S-band type at 2.8 Ghz) to have the same 10 dBZ echo top height as those simulated. These suggest a fairly significant mean moistening of 0.26, 0.13 and 0.05 ppmv in the strongest, medium and weakest cases, respectively, for heights between 16 and 17 km. Since the cold point and WMO (World Meteorological Organization) tropopause in this region lies at ~15.9 km, this is likely to represent direct stratospheric moistening. Much more moistening is predicted for the 15–16 km height range with increases of 0.85–2.8 ppmv predicted. However, it would be required that this air is lofted through the tropopause via the Brewer Dobson circulation in order for it to have a stratospheric effect. Whether this is likely is uncertain and, in addition, the dehydration of air as it passes through the cold trap and the number of times that trajectories sample convective regions needs to be taken into account to gauge the overall stratospheric effect. Nevertheless, the results suggest a potentially significant role for convection in determining the stratospheric water content. Sensitivity tests exploring the impact of increased aerosol numbers in the boundary layer suggest that a corresponding rise in cloud droplet numbers at cloud base would increase the number concentrations of the ice crystals transported to the TTL, which had the effect of reducing the fall speeds of the ice and causing a ~13% rise in the mean vapour increase in both the 15–16 and 16–17 km height ranges, respectively, when compared to the control case. Increases in the total water were much larger, being 34% and 132% higher for the same height ranges, but it is unclear whether the extra ice will be able to evaporate before precipitating from the region. These results suggest a possible impact of natural and anthropogenic aerosols on how convective clouds affect stratospheric moisture levels.

The Role of Entrainment in the Diurnal Cycle of Continental Convection

2010 ◽  
Vol 23 (10) ◽  
pp. 2722-2738 ◽  
Author(s):  
Anthony D. Del Genio ◽  
Jingbo Wu
Keyword(s):  
Diurnal Cycle ◽  
General Circulation ◽  
Free Parameter ◽  
Deep Convection ◽  
Wrf Model ◽  
Time Of Day ◽  
Cloud Base ◽  
Cold Pool ◽  
Entrainment Rate ◽  
Cumulus Parameterizations

Abstract In continental convective environments, general circulation models typically produce a diurnal cycle of rainfall that peaks close to the noon maximum of insolation, hours earlier than the observed peak. One possible reason is insufficient sensitivity of their cumulus parameterizations to the state of the environment due to weak entrainment. The Weather Research and Forecasting (WRF) model, run at cloud-resolving (600 and 125 m) resolution, is used to study the diurnal transition from shallow to deep convection during the monsoon break period of the Tropical Warm Pool–International Cloud Experiment. The WRF model develops a transition from shallow to deep convection in isolated events by 1430–1500 local time. The inferred entrainment rate weakens with increasing time of day as convection deepens. Several current cumulus parameterizations are tested for their ability to reproduce the WRF behavior. The Gregory parameterization, in which entrainment rate varies directly with parcel buoyancy and inversely as the square of the updraft speed, is the best predictor of the inferred WRF entrainment profiles. The Gregory scheme depends on a free parameter that represents the fraction of buoyant turbulent kinetic energy generation on the cloud scale that is consumed by the turbulent entrainment process at smaller scales. A single vertical profile of this free parameter, increasing with height above the boundary layer but constant with varying convection depth, produces entrainment rate profiles consistent with those inferred from the WRF over the buoyant depth of the convection. Parameterizations in which entrainment varies inversely with altitude or updraft speed or increases with decreasing tropospheric relative humidity do not perform as well. Entrainment rate at cloud base decreases as convection depth increases; this behavior appears to be related to an increase in vertical velocity at downdraft cold pool edges.

scholarly journals A study of the effect of overshooting deep convection on the water content of the TTL and lower stratosphere from Cloud Resolving Model simulations

2007 ◽  
Vol 7 (3) ◽  
pp. 7277-7346 ◽  
Author(s):  
D. P. Grosvenor ◽  
T. W. Choularton ◽  
H. Coe ◽  
G. Held
Keyword(s):  
Boundary Layer ◽  
Water Content ◽  
Lower Stratosphere ◽  
Deep Convection ◽  
Cold Trap ◽  
Cloud Base ◽  
Anthropogenic Aerosols ◽  
Height Range ◽  
Cloud Resolving Model ◽  
The Impact

Abstract. Simulations of overshooting, tropical deep convection using a Cloud Resolving Model with bulk microphysics are presented in order to examine the effect on the water content of the TTL (Tropical Tropopause Layer) and lower stratosphere. This case study is a subproject of the HIBISUCS (Impact of tropical convection on the upper troposphere and lower stratosphere at global scale) campaign, which took place in Bauru, Brazil (22° S), from the end of January to early March 2004. Comparisons between 2-D and 3-D simulations suggest that the use of 3-D dynamics is vital in order to capture the mixing between the overshoot and the stratospheric air, which caused evaporation of ice and resulted in an overall moistening of the lower stratosphere. In contrast, a dehydrating effect was predicted by the 2-D simulation due to the extra time, allowed by the lack of mixing, for the ice transported to the region to precipitate out of the overshoot air. Three different strengths of convection are simulated in 3-D by applying successively lower heating rates (used to initiate the convection) in the boundary layer. Moistening is produced in all cases, indicating that convective vigour is not a factor in whether moistening or dehydration is predicted, since the weakest case only just penetrated the tropopause. An estimate of the moistening effect of these clouds on an air parcel traversing a convective region is made based on the domain mean simulated moistening and the frequency of convective events observed by the IPMet (Instituto de Pesquisas Meteorológicas, Universidade Estadual Paulista) radar to have the same 10 dBZ echo top height as those simulated. These suggest a fairly significant mean moistening of 0.26, 0.13 and 0.05 ppmv in the strongest, medium and weakest cases, respectively, for heights between 16 and 17 km. Since the tropopause in this region is thought to lie at ~15.9 km, this is likely to represent direct stratospheric moistening. Much more moistening is predicted for the 15–16 km height range with increases of 0.85–2.8 ppmv predicted. However, it would be required that this air is lofted through the tropopause via the Brewer Dobson circulation in order for it to have a stratospheric effect. Whether this is likely is uncertain and, in addition, the dehydration of air as it passes through the cold trap and the number of times that trajectories sample convective regions needs to be taken into account to gauge the overall stratospheric effect. Nevertheless, the results suggest a potentially significant role for convection in determining the stratospheric water content. Sensitivity tests exploring the impact of increased aerosol numbers in the boundary layer suggest that a corresponding rise in cloud droplet numbers at cloud base would increase the number concentrations of the ice crystals transported to the TTL, which had the effect of reducing the fall speeds of the ice and causing a ~13% rise in the mean vapour increase in both the 15–16 and 16–17 km height ranges, respectively, when compared to the control case. Increases in the total water were much larger, being 34% and 132% higher for the same height ranges, but it is unclear whether the extra ice will be able to evaporate before precipitating from the region. These results suggest a possible impact of natural and anthropogenic aerosols on how convective clouds affect stratospheric moisture levels.

scholarly journals Updraft Constraints on Entrainment: Insights from Amazonian Deep Convection

2019 ◽  
Vol 76 (8) ◽  
pp. 2429-2442 ◽  
Author(s):  
Usama M. Anber ◽  
Scott E. Giangrande ◽  
Leo J. Donner ◽  
Michael P. Jensen
Keyword(s):  
Ad Hoc ◽  
Prediction Models ◽  
Mixing Time ◽  
Deep Convection ◽  
Weather Prediction ◽  
Limited Area ◽  
Grid Cells ◽  
Model Simulations ◽  
Cloud Resolving Model ◽  
Environmental Air

AbstractMixing of environmental air into clouds, or entrainment, has been identified as a major contributor to erroneous climate predictions made by modern comprehensive climate and numerical weather prediction models. Despite receiving extensive attention, the ad hoc treatment of this convective-scale process in global models remains poor. On the other hand, while limited-area high-resolution nonhydrostatic models can directly resolve entrainment, their sensitivity to model resolution, especially with the lack of benchmark mass flux observations, limits their applicability. Here, the dataset from the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) campaign focusing on radar retrievals of convective updraft vertical velocities is used with the aid of cloud-resolving model simulations of four deep convective events over the Amazon to provide insights into entrainment. Entrainment and detrainment are diagnosed from the model simulations by applying the mass continuity equation over cloud volumes, in which grid cells are identified by some thresholds of updraft vertical velocity and cloud condensates, and accounting for the sources and sinks of the air mass. Entrainment is then defined as the environmental air intruding into convective cores causing cloud volume to shrink, while detrainment is defined as cloudy grid cells departing the convective core and causing cloud volume to expand. It is found that the diagnosed entrainment from the simulated convective events is strongly correlated to the inverse of the updraft vertical velocities in convective cores, which enables a more robust estimation of the mixing time scale. This highlights the need for improved observational capabilities for sampling updraft velocities across diverse geographic and cloud conditions. Evaluation of a number of assumptions used to represent entrainment in parameterization schemes is also presented, as contrasted against the diagnosed one.

scholarly journals Observation of the Tropical Cyclone Diurnal Cycle Using Hyperspectral Infrared Satellite Sounding Retrievals

2021 ◽  
Author(s):  
Erika L. Duran ◽  
Emily B. Berndt ◽  
Patrick Duran
Keyword(s):  
Tropical Cyclone ◽  
Diurnal Cycle ◽  
Inner Core ◽  
Deep Layer ◽  
Deep Convection ◽  
Satellite System ◽  
Radiative Heating ◽  
Lapse Rate ◽  
Vertical Profiles ◽  
Microwave Sounding

AbstractHyperspectral infrared satellite sounding retrievals are used to examine thermodynamic changes in the tropical cyclone (TC) environment associated with the diurnal cycle of radiation. Vertical profiles of temperature and moisture are retrieved from the Suomi National Polar–orbiting Partnership (S–NPP) satellite system, National Oceanic and Atmospheric Administration (NOAA)–20, and the Meteorological Operational (MetOp) A/B satellite system, leveraging both infrared and microwave sounding technologies. Vertical profiles are binned radially based on distance from the storm center and composited at 4–hr intervals to reveal the evolution of the diurnal cycle. For the three cases examined – Hurricane Dorian (2019), Hurricane Florence (2018) and Hurricane Irma (2017) – a marked diurnal signal is evident that extends through a deep layer of the troposphere. Statistically significant differences at the 95% level are observed in temperature, moisture, and lapse rate profiles, indicating a moistening and destabilization of the mid to upper troposphere that is more pronounced near the inner core of the TC at night. Observations support a favorable environment for the formation of deep convection caused by diurnal differences in radiative heating tendencies, which could partially explain why new diurnal pulses tend to form around sunset. These findings demonstrate that the diurnal cycle of radiation affects TC thermodynamics through a deep layer of the troposphere, and suggest that hyperspectral infrared satellite sounding retrievals are valuable assets in detecting thermodynamic variations in TCs.

scholarly journals Evaluating Boundary Layer–Based Mass Flux Closures Using Cloud-Resolving Model Simulations of Deep Convection

2010 ◽  
Vol 67 (7) ◽  
pp. 2212-2225 ◽  
Author(s):  
Jennifer K. Fletcher ◽  
Christopher S. Bretherton
Keyword(s):  
Boundary Layer ◽  
Mass Flux ◽  
Large Scale ◽  
Deep Convection ◽  
Cloud Base ◽  
Cumulus Convection ◽  
Model Simulations ◽  
Shallow Cumulus ◽  
Wide Range ◽  
Cloud Resolving Model

Abstract High-resolution three-dimensional cloud resolving model simulations of deep cumulus convection under a wide range of large-scale forcings are used to evaluate a mass flux closure based on boundary layer convective inhibition (CIN) that has previously been applied in parameterizations of shallow cumulus convection. With minor modifications, it is also found to perform well for deep oceanic and continental cumulus convection, and it matches simulated cloud-base mass flux much better than a closure based only on the boundary layer convective velocity scale. CIN closure maintains an important feedback among cumulus base mass flux, compensating subsidence, and CIN that keeps the boundary layer top close to cloud base. For deep convection, the proposed CIN closure requires prediction of a boundary layer mean turbulent kinetic energy (TKE) and a horizontal moisture variance, both of which are strongly correlated with precipitation. For our cases, CIN closure predicts cloud-base mass flux in deep convective environments as well as the best possible bulk entraining CAPE closure, but unlike the latter, CIN closure also works well for shallow cumulus convection without retuning of parameters.

A modelling perspective on anvil evolution differences between day and night

2021 ◽  
Author(s):  
Blaž Gasparini ◽  
Adam Sokol ◽  
Casey Wall ◽  
Dennis Hartmann ◽  
Peter Blossey
Keyword(s):  
Diurnal Cycle ◽  
Deep Convection ◽  
Cloud Fraction ◽  
Number Concentration ◽  
Shortwave Radiation ◽  
Ice Crystal ◽  
Ice Water Content ◽  
Environmental Air ◽  
Ice Water

<p>Geostationary satellite observations of tropical maritime convection indicate an afternoon maximum in anvil cloud fraction that cannot be explained by the diurnal cycle of deep convection peaking in the night. This implies that the daytime anvils must be more widespread and/or long lived compared with the anvils that are formed during the night.</p><p>We study the decay of anvil clouds in an idealized cloud resolving modelling setup in which a cloud is initialized in the middle of the model domain to identify what causes differences in the evolution depending on the time of the day in which the cloud is detrained from a deep convective core. We show that daytime anvils are both longer lived and more widespread. The main reason for their longevity is the heating due to absorption of shortwave radiation, which leads to a mesoscale ascent within the cloud, helping to loft and spread the cloud further than the nighttime anvils. The nighttime anvil cloud top is dominated by longwave radiative cooling, which drives a circulation that erodes the cloud top by entrainment of drier environmental air and leads to a cloud descent and shorter lifetime. </p><p>Additional simulations in radiative convective equilibrium setup with a realistic diurnal cycle of insolation confirm the crucial role of shortwave heating in increasing the daytime anvil cloud top and anvil longevity. In addition, the mesoscale ascent also modifies daytime anvil properties, leading to an increased ice water content, higher ice crystal number concentration and larger ice crystal radius near cloud top.</p>

scholarly journals Characteristics of Cloud Systems over the Tibetan Plateau and East China during Boreal Summer

2017 ◽  
Vol 30 (9) ◽  
pp. 3117-3137 ◽  
Author(s):  
Jinghua Chen ◽  
Xiaoqing Wu ◽  
Yan Yin ◽  
Qian Huang ◽  
Hui Xiao
Keyword(s):  
Tibetan Plateau ◽  
Diurnal Cycle ◽  
Convective Cloud ◽  
Radiative Heating ◽  
East China ◽  
Boreal Summer ◽  
The Tibetan Plateau ◽  
Cloud Systems ◽  
Convective Clouds ◽  
Cloud Resolving Model

Constrained by ERA-Interim, a cloud-resolving model is employed to characterize cloud systems over the Tibetan Plateau (TP) and east China. The authors focus on analyzing the role of different physical processes on cloud macro- and microscale properties of the cloud systems, especially convective cloud systems between east China and the TP. It is found that convective clouds over the TP are thinner than over east China. This difference is also reflected in the albedo at the top of the atmosphere, where smaller albedos are found for the clouds over the TP. Furthermore, the lifetimes of the deep cloud systems over the TP are shorter than over east China. For the entire simulated period, the latent heat released by phase transitions contributes the most to the total heating and moisture budget, followed by eddy transport over all regions. In addition, radiative heating also plays a nonnegligible role in the total heating effects over the TP. These results also suggest that the influence of ice phase processes is more important over the TP than east China, especially during deep convective periods. Affected by strong surface heat flux, the cloud-top height of convective clouds over the TP exhibits a diurnal cycle, leading to a diurnal cycle of rainfall.

scholarly journals Latent Heating and Mixing due to Entrainment in Tropical Deep Convection

2014 ◽  
Vol 71 (2) ◽  
pp. 816-832 ◽  
Author(s):  
Clayton J. McGee ◽  
Susan C. van den Heever
Keyword(s):  
High Resolution ◽  
Deep Convection ◽  
Potential Temperature ◽  
Latent Heating ◽  
Freezing Level ◽  
Tropical Deep Convection ◽  
Cloud Resolving Model ◽  
Nested Grid ◽  
Environmental Air ◽  
Convective Cells

Abstract Recent studies have noted the role of latent heating above the freezing level in reconciling Riehl and Malkus' hot tower hypothesis (HTH) with evidence of diluted tropical deep convective cores. This study evaluates recent modifications to the HTH through Lagrangian trajectory analysis of deep convective cores in an idealized, high-resolution cloud-resolving model (CRM) simulation that uses a sophisticated two-moment microphysical scheme. A line of tropical convective cells develops within a finer nested grid whose boundary conditions are obtained from a large-domain CRM simulation approaching radiative convective equilibrium (RCE). Microphysical impacts on latent heating and equivalent potential temperature (θe) are analyzed along trajectories ascending within convective regions of the high-resolution nested grid. Changes in θe along backward trajectories are partitioned into contributions from latent heating due to ice processes and a residual term that is shown to be an approximate representation of mixing. The simulations demonstrate that mixing with dry environmental air decreases θe along ascending trajectories below the freezing level, while latent heating due to freezing and vapor deposition increase θe above the freezing level. Latent heating contributions along trajectories from cloud nucleation, condensation, evaporation, freezing, deposition, and sublimation are also quantified. Finally, the source regions of trajectories reaching the upper troposphere are identified. Much of the air ascending within convective updrafts originates from above the lowest 2 km AGL, but the strongest updrafts are composed of air from closer to the surface. The importance of both boundary layer and midlevel inflow in moist environments is underscored in this study.

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