Convective Area Research Articles

Relationship Between Summer Precipitation in North China and Madden–Julian Oscillation During the Boreal Summer of 2018

Based on the data about summer precipitation in North China, tropical MJO (short for Madden-Julian Oscillation) index, and NCEP/NCAR (short for National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis data, this paper analyzed the relationship between summer precipitation 2018 in North China and MJO by using multiple statistical methods. Findings indicate that, (1) Summer precipitation in North China is closely related to MJO. During the times when the MJO was in phases 5 and 6, North China had heavy precipitation. (2) The correlation mechanism is mainly: At 850 hPa, when MJO storm clouds move eastward, anticyclonic circulation is excited in the north side of the convection area, thus forming a pair of cyclones and anticyclones. Though MJO storm clouds cannot move northward to higher latitude to have direct impact on the summer precipitation in North China, the anticyclonic circulation on the north side of cyclones during the eastward movement of MJO to phases 5 and 6 can strengthen the water-vapor transfer of southerly wind (corresponding to RMM1) or that of southeast wind (corresponding to RMM2) in summer in North China, thus providing favorable water-vapor conditions for precipitation in North China. At 500 hPa, when MJO moves eastward into phases 5 and 6, the western Pacific subtropical high will move northward to the area near the Korean Peninsula and be strengthened, thus blocking weather systems that come from the west, and facilitating ascending motions in North China. At 200 hPa, MJO-associated convection will generate disturbances at upper troposphere and transmit the impacts of disturbances to downstream areas along the westerly jet waveguide, thus forming a disturbance wave train. When MJO moves eastward into phases 5 and 6, duing to the effect of wave train propagation, disturbances at the height of the 500 hPa pressure will have a positive anomaly near the Korean Peninsula, forming an obvious barotropic structure with 500 hPa subtropical high, which strengthens the blocking to weather systems that come from the west and is favorable to the precipitation in North China. (3) MJO can be used for extended-range forecast of summer precipitation over North China.

Thermal analysis of a binary base fluid in pool boiling system of glycol–water alumina nano-suspension

The main aim of the present research is to measure the nucleate boiling heat transfer coefficient (BHTC) of aqueous glycol nano-suspension as a coolant around a horizontal heater. Alumina nanoparticles were added to the base fluid at a volumetric concentration of 1% to improve the thermal conductivity of the nano-suspension. The pressure of the system was set to the atmospheric pressure, and the coolant was tested at different applied heat fluxes (HF) ranged from 0 to 90 kW m−2 and volumetric concentration of 0–40% of the heavier component. Two zones of heat transfer were identified, including a natural convection zone and nucleate boiling one mixed with bubble formation and bubble interactions. Results also showed that the HTC of the nano-suspension is smaller than those recorded for the pure water. A rough comparison was made to examine the accuracy of the developed equations for estimating the BHTC value against the experimental data. It was found that the developed equations are not accurate for the data measured in the free convection region. Thus, the Churchill-Chu correlation was recommended for estimating the BHTC in the free convection area of heat transfer. Also, the effect of operating parameters such as HF and volumetric concentration on the pool boiling HTC of the solution was studied.

Eddies in the North Greenland Sea and Fram Strait From Satellite Altimetry, SAR and High‐Resolution Model Data

AbstractIn this study, we investigate eddy dynamics in the northern Greenland Sea and the Fram Strait using AVISO altimetry, spaceborne synthetic aperture radar (SAR), and Finite Element Sea ice‐Ocean Model (FESOM) high‐resolution numerical model data. In the region, eddies are thought to play an important role in the redistribution of the warmer and saltier Atlantic Water between the Arctic Ocean and the areas of deep convection in the central Greenland Sea. We found that eddies detected in AVISO and in SAR form two complementary data sets of large mesoscale eddies (with typical radii of 30–50 km) and of small mesoscale/submesoscale eddies (with typical radii of 1–5 km and not exceeding 30 km), respectively. For large mesoscale eddies, the number of cyclones and anticyclones is approximately the same, while for submesoscale eddies, cyclones are strongly dominating. The limitations and possible biases in each of the data sets are discussed and cross‐validated against FESOM results. It is noted that the most energetic eddies are concentrated along the major currents and in the northern part of the region. Eddy translations follow the mean currents in their overall cyclonic circulation around the northern Greenland Sea. A convergence of the eddies toward the Nordbukta area is detected. On seasonal time scale, a higher number of more intense mesoscale eddies is observed during winter, associated with a quasi‐simultaneous intensification of the mean currents. Model results also show an increase in the number of small eddies in spring‐early summer attributed to the decay of large eddies, while in late autumn, the opposite tendency suggests eddy merger.

Fire smoke movement and distribution in ventilation shafts

Vertical shafts are common structures in buildings, which accelerate smoke spread in fires due to stack effect. In this study, fire smoke movement and distribution in a ventilation shaft were studied through analysing temperature distributions, velocity distributions, CO2 concentration distributions and pressure distributions. Four exhaust rates were discussed and compared. It was found that the status of gas flow at the bottom of the shaft was firstly disturbed when the exhaust fan was working. Then some eddies appeared. As the number of eddies was increased and eddies got enlarged, gas flow in the entire shaft was influenced from the bottom to the top. A high temperature area and a strong convection area appeared close to the open door which was located at the bottom of the shaft. When the exhaust fan was working, the high temperature area and the strong convection area were both controlled at lower positions. The CO2 concentration and the pressure in the shaft were negatively related to the exhaust rate, while the neutral pressure plane height was positively related to the exhaust rate.

Quantitative analysis of trapezoid baffle block sloping angles on oxygen transport and performance of proton exchange membrane fuel cell

Increasing the power density of proton exchange membrane (PEM) fuel cell without extra cost through flow channel design is an effective method to achieve cost and compact requirement of its commercialization for vehicles. PEM fuel cell power or current density is mainly limited by oxygen transport to the reacting sites in the cathode porous electrode. Inserting baffle blocks in the flow channel of PEM fuel cell can effectively enhance the oxygen transport and fuel cell performance. However, existing researches on the structure design of baffle blocks are still insufficient, especially for the design of baffle block sloping angles. In this study, the influence of the trapezoid baffle block sloping angles on the convective and diffusive oxygen transport and performance of PEM fuel cell is quantitatively investigated using a three-dimensional numerical model. The results indicate that larger leading angle of the baffle block leads to a higher gas velocity component in the vertical direction, hence enhances the convective oxygen transport effect; but it reduces the convection area, as well as the oxygen delivery efficiency in the channel. Larger trailing angle of the baffle block induces the back-flow phenomenon at the rear of the baffle block, which causes the loss of gas pressure and worse oxygen transport. Both the baffle block sloping angles are carefully designed, and it demonstrates that the trapezoid baffle blocks with both the leading and trailing sloping angles of 45° show the best oxygen transport and fuel cell performance.

Atlantic Meridional Overturning Circulation and δ13C Variability During the Last Interglacial

AbstractThe Atlantic Meridional Overturning Circulation (AMOC) is thought to be relatively vigorous and stable during Interglacial periods on multimillennial (equilibrium) timescales. However, recent proxy (δ13C benthic) reconstructions suggest that higher frequency variability in deep water circulation may have been common during some interglacial periods, including the Last Interglacial (LIG, 130–115 ka). The origin of these isotope variations and their implications for past AMOC remain poorly understood. Using iLOVECLIM, an Earth system model of intermediate complexity (EMIC) allowing the computation of and direct comparison to proxy reconstructions, we perform a transient experiment of the LIG (125–115 ka) forced only by boundary conditions of greenhouse gases and orbital forcings. The model simulates large centennial‐scale variations in the interior of the North Atlantic similar in timescale and amplitude to changes resolved by high‐resolution reconstructions from the LIG. In the model, these variations are caused by changes in the relative influence of North Atlantic Deep Water (NADW) and southern source water (SSW) and are closely linked to large (∼50%) changes in AMOC strength provoked by saline input and associated deep convection areas south of Greenland. We identify regions within the subpolar North Atlantic with different sensitivity and response to changes in preformed of NADW and to changes in NADW versus SSW influence, which is useful for proxy record interpretation. This could explain the relatively large δ13C gradient (∼0.4%0) observed at ∼3 km water depth in the subpolar North Atlantic at the inception of the last glacial.

Impact of the Boreal Summer Intraseasonal Oscillation on the Diurnal Cycle of Precipitation near and over the Island of Luzon

AbstractDuring the boreal summer, satellite-based precipitation estimates indicate a distinct maximum in rainfall off the west coast of the island of Luzon in the Philippines. Also occurring during the summer months is the boreal summer intraseasonal oscillation (BSISO), a main driver of intraseasonal variability in the region. This study investigates the diurnal variability of convective intensity, morphology, and precipitation coverage offshore and over the island of Luzon. The results are then composited by BSISO activity. Results of this study indicate that offshore precipitation is markedly increased during active BSISO phases, when strong low-level southwesterly monsoon winds bring increased moisture and enhanced convergence upwind of the island’s high terrain. A key finding of this work is the existence of an afternoon maximum in convection over Luzon even during active BSISO phases, when solar heating and instability are apparently reduced due to enhanced cloud cover. This result is important, as previous studies have shown in other areas of the tropics afternoon convection over landmasses is a key component to offshore precipitation. Although offshore precipitation is maximized in the evening hours during active phases, results indicate that precipitation frequently occurs over the ocean around the clock (both as organized systems and isolated, shallow showers), possibly owing to an increase in sensible and latent heat fluxes, vertical wind shear, and convergence of the monsoon flow with land features.

A Numerical Simulation of Mass Transport in Deep Convection over the Tibet Plateau

By using the WRF-Chem model to simulate a deep convection process that occurred in the eastern part of the Tibetan Plateau, the vertical transport process and main mechanisms of water and ozone in the upper troposphere-lower stratosphere were studied. The air in the lower layer of the troposphere, which is rich in water vapor and low ozone concentration, is transported near the top of the troposphere. The enhancement of convective motion causes the height of the troposphere to rise and the temperature to decrease. Therefore, water vapor is prone to condensation and dehydration, and ice crystals are formed near the top of the troposphere, resulting in a low value zone of water vapor at 100 hPa. By analyzing the distribution of ozone, it is found that there is a high concentration of ozone transported on both sides of the deep convection area. The stronger the convection, the stronger the downward transport. It further explains that this deep convection process not only causes the upward transport of tropospheric air in the deep convection area, but also causes the transport of stratospheric air to the troposphere on both sides of the deep convection area.

Global Survey of Precipitation Properties Observed during Tropical Cyclogenesis and Their Differences Compared to Nondeveloping Disturbances

Abstract This study evaluates precipitation properties involved in tropical cyclogenesis by analyzing a multiyear, global database of passive microwave overpasses of the pregenesis stage of developing disturbances and nondeveloping disturbances. Precipitation statistics are quantified using brightness temperature proxies from the 85–91-GHz channels of multiple spaceborne sensors, as well as retrieved rain rates. Proxies focus on the overall raining area, areal coverage of deep convection, and the proximity of precipitation to the disturbance center. Of interest are the differences in those proxies for developing versus nondeveloping disturbances, how the properties evolve during the pregenesis stage, and how they differ globally. The results indicate that, of all of the proxies examined, the total raining area and rain volume near the circulation center are the most useful precipitation-related predictors for genesis. The areal coverage of deep convection also differentiates developing from nondeveloping disturbances and, similar to the total raining area, generally also increases during the pregenesis stage, particularly within a day of genesis. As the threshold convective intensity is increased, pregenesis cases are less distinguishable from nondeveloping disturbances. Relative to the western Pacific and Indian Oceans, the Atlantic and eastern North Pacific Oceans have less precipitation and deep convection observed during genesis and the smallest differences between developing and nondeveloping disturbances. This suggests that the total raining area and areal coverage of deep convection associated with tropical disturbances are better predictors of tropical cyclogenesis fate in the Pacific and Indian Oceans than in the Atlantic and eastern North Pacific.

Relationship between extreme rainfall based on GSMaP data with Madden Julian Oscillation (MJO) in Bangka Island

The effect of MJO events on extreme rainfall events on Bangka Island needs to be spatially studied in more detail. The low quality of rain station data encourages the use of alternative data such as Global Satellite Mapping of Precipitation (GSMaP). This study aimed to analyze the influence of active MJO on extreme rainfall events using GSMaP data on Bangka Island. The methods used are extreme threshold of 95th, 98th and 99th percentile, the Spearman Rank correlation between extreme rainfall events and active MJO and its correlation significance test. The results showed that northern coast has the highest range of extreme threshold. The correlation significance test showed GSMaP grids that have a significant correlation with the MJO are in the north of the Island, especially coast area. MJO phases 3 and 5 have an impact on decreasing of extreme rainfall events which are known through the negative correlation values. From all the three extreme thresholds, it was only MJO phase 4 that increasing extreme rainfall events. Active MJO phase 4 causes Bangka Island as a convective area, while MJO phases 3 and 5 affect the formation of suppressed areas on Bangka Island.

A Machine Learning Assisted Development of a Model for the Populations of Convective and Stratiform Clouds

AbstractTraditional parameterizations of the interaction between convection and the environment have relied on an assumption that the slowly varying large‐scale environment is in statistical equilibrium with a large number of small and short‐lived convective clouds. They fail to capture nonequilibrium transitions such as the diurnal cycle and the formation of mesoscale convective systems as well as observed precipitation statistics and extremes. Informed by analysis of radar observations, cloud‐permitting model simulation, theory, and machine learning, this work presents a new stochastic cloud population dynamics model for characterizing the interactions between convective and stratiform clouds, with the goal of informing the representation of these interactions in global climate models. Fifteen wet seasons of precipitating cloud observations by a C‐band radar at Darwin, Australia are fed into a machine learning algorithm to obtain transition functions that close a set of coupled equations relating large‐scale forcing, mass flux, the convective cell size distribution, and the stratiform area. Under realistic large‐scale forcing, the derived transition functions show that, on the one hand, interactions with stratiform clouds act to dampen the variability in the size and number of convective cells and therefore in the convective mass flux. On the other, for a given convective area fraction, a larger number of smaller cells is more favorable for the growth of stratiform area than a smaller number of larger cells. The combination of these two factors gives rise to solutions with a few convective cells embedded in a large stratiform area, reminiscent of mesoscale convective systems.

Assimilation of Radar Data, Pseudo Water Vapor, and Potential Temperature in a 3DVAR Framework for Improving Precipitation Forecast of Severe Weather Events

An improved approach to derive pseudo water vapor mass mixing ratio and in- cloud potential temperature was developed in this paper to better initialize numerical weather prediction (NWP) and build convective-scale predictions of severe weather events. The process included several steps. The first was to identify areas of deep moist convection, utilizing Vertically Integrated Liquid water (VIL) derived from a mosaicked 3D radar reflectivity field. Then, pseudo- water vapor and pseudo- in- cloud potential temperature observations were derived based on the VIL. For potential temperature, the latent heat initialization for stratiform cloud and moist adiabatic initialization for deep moist convection were used based on a cloud analysis method. The third step was to assimilate the derived pseudo- water vapor and potential temperature observations, together with radar radial velocity and reflectivity into a convective-scale NWP model during data assimilation cycles spanning several hours. Finally, 3-h forecasts were launched each hour during the data assimilation period. The effects of radar data and pseudo- observation assimilation on the prediction of rainfall associated with convective systems surrounding the Meiyu front in 2018 were explored using two real cases. Two sets of experiments, each including several experiments in each real case, were designed to compare the effects of assimilation radar and pseudo- observations on the ensuing forecasts. Relative to the control experiment without data assimilation and radar experiment, the analyses and forecasts of convections were found to be improved for the two Meiyu front cases after pseudo- water vapor and potential temperature information was assimilated.

Natural drivers of multidecadal Arctic sea ice variability over the last millennium

The climate varies due to human activity, natural climate cycles, and natural events external to the climate system. Understanding the different roles played by these drivers of variability is fundamental to predicting near-term climate change and changing extremes, and to attributing observed change to anthropogenic or natural factors. Natural drivers such as large explosive volcanic eruptions or multidecadal cycles in ocean circulation occur infrequently and are therefore poorly represented within the observational record. Here we turn to the first high-latitude annually-resolved and absolutely dated marine record spanning the last millennium, and the Paleoclimate Modelling Intercomparison Project (PMIP) Phase 3 Last Millennium climate model ensemble spanning the same time period, to examine the influence of natural climate drivers on Arctic sea ice. We show that bivalve oxygen isotope data are recording multidecadal Arctic sea ice variability and through the climate model ensemble demonstrate that external natural drivers explain up to third of this variability. Natural external forcing causes changes in sea-ice mediated export of freshwater into areas of active deep convection, affecting the strength of the Atlantic Meridional Overturning Circulation (AMOC) and thereby northward heat transport to the Arctic. This in turn leads to sustained anomalies in sea ice extent. The models capture these positive feedbacks, giving us improved confidence in their ability to simulate future sea ice in in a rapidly evolving Arctic.

Backward Adaptive Brightness Temperature Threshold Technique (BAB3T): A Methodology to Determine Extreme Convective Initiation Regions Using Satellite Infrared Imagery

Thunderstorms in southeastern South America (SESA) stand out in satellite observations as being among the strongest on Earth in terms of satellite-based convective proxies, such as lightning flash rate per storm, the prevalence for extremely tall, wide convective cores and broad stratiform regions. Accurately quantifying when and where strong convection is initiated presents great interest in operational forecasting and convective system process studies due to the relationship between convective storms and severe weather phenomena. This paper generates a novel methodology to determine convective initiation (CI) signatures associated with extreme convective systems, including extreme events. Based on the well-established area-overlapping technique, an adaptive brightness temperature threshold for identification and backward tracking with infrared data is introduced in order to better identify areas of deep convection associated with and embedded within larger cloud clusters. This is particularly important over SESA because ground-based weather radar observations are currently limited to particular areas. Extreme rain precipitation features (ERPFs) from Tropical Rainfall Measurement Mission are examined to quantify the full satellite-observed life cycle of extreme convective events, although this technique allows examination of other intense convection proxies such as the identification of overshooting tops. CI annual and diurnal cycles are analyzed and distinctive behaviors are observed for different regions over SESA. It is found that near principal mountain barriers, a bimodal diurnal CI distribution is observed denoting the existence of multiple CI triggers, while convective initiation over flat terrain has a maximum frequency in the afternoon.

Motion behaviour of ellipsoidal granular system under vertical vibration and airflow

We studied the motion behaviour of ellipsoid particles under vertical vibration and airflow. Three typical convection patterns were observed when submitted to vertical vibration with frequency (f) from 20 Hz to 80 Hz and dimensionless vibration acceleration (Γ) from one to six. We studied the effects of f and Γ on the change of convection patterns. We quantitatively studied the effects of f, Γ, airflow direction, airflow velocity, and particle shape on the convection area and intensity using the area fraction λ and average velocity vz characterizing the convection area and intensity, respectively. Results showed that the convection first occured occurred in the upper part of the granular system. Increasing f and A can both increase the convection area and strengthen the convection intensity. A had a greater influence than f at the same Γ. The wheat particles were more likely to enter the global convection state under the action of the airflow in the opposite direction of gravity. The maximum convection intensity of wheat particles under the airflow in the opposite direction of gravity was approximately 30-35% of the value measured under the airflow along the direction of gravity. The convection area and maximum convection intensity of the spherical particles were approximately 85% and 93% of the measured values for the ellipsoidal particles, respectively. We also analysed the effects of f, Γ, airflow direction, airflow velocity, and particle shape on the convection area on the basis of energy dissipation.

Heat Transfer Properties in Microchannel by Varying Aspect Ratio: Experimental and Simulation

In this paper study the heat transfer rate in a branched and rectangular micro channel. Using the aspect ratio of height and width were 1:1 for straight channel and 0.75/1 for branched channel. This experiment was done for same convective area 60 mm2. This experiment was study how to affect the aspect ratio to temperature drop. The change of effect the aspect ratio we are found by simulation by using the other branch channel aspect ratio (1) or straight micro channel aspect ratio (1.37) and the same area 47mm2. These different aspect ratio straight and branched channels compare to each other. Then studied after this experimental data as a function of aspect ratio increase the 20% of friction constant evidence at low aspect ratio. Then the wall temperature is carried 92⁰c and heating the heat sink at 90 watts. Using the convective heat transfer in the micro-channel. Study the effect of varying aspect ratio for both branched and rectangular micro-channel has analysed in this study and experimentally performed. Analysis of heat transfer by varying the Nusselt number. The effect of varying Nusselt number or temperature difference on both straight micro-channels and branched micro-channel was studied.

Simulating a Mesoscale Convective System Using WRF With a New Spectral Bin Microphysics: 1: Hail vs Graupel

AbstractA modified Fast Spectral Bin Microphysics scheme (FSBM‐2) embedded into the Weather Research and Forecasting (WRF) model is used to simulate a mesoscale deep convective system observed during the Midlatitude Continental Convective Clouds Experiment (MC3E). FSBM‐2 uses modified source codes as compared to the current FSBM (FSBM‐1). In contrast to FSBM‐1, FSBM‐2 can simulate hail of several centimeters in diameter and includes additional processes such as spontaneous breakup of raindrops and aerosol regeneration by drop evaporation. It is shown that allowing large hail particles of diameters exceeding about 1 cm substantially increases the agreement between the simulated and observed squall‐line structures in both the convective and stratiform regions. In contrast, if graupel particles are used to represent high‐density hydrometeors in convective areas, the ratio of convective‐to‐stratiform areas diverges from the ratio seen in observations and maximum radar reflectivities are substantially underestimated. Analysis of snow size distributions in the stratiform area shows an important link between the ice crystals formed by homogeneous freezing in the convective area to ice particle number concentration in the stratiform region. Simulated raindrop size distributions in the stratiform area below the melting level from FSBM‐2 show a good agreement with observations. The regeneration of cloud condensational nuclei (CCN) by droplet evaporation and detrainment of these CCN to the stratiform region increases the concentration of CCN there up to 8‐ to 9‐km altitude; the additional CCN penetrate clouds and produce new droplets, leading to some convection intensification.

Mechanism for Increasing Tropical Rainfall Unevenness With Global Warming

AbstractGlobal climate models predict that tropical rainfall will be distributed more unevenly with global warming; that is, dry regions or months will get drier and wet regions or months will get wetter. Previous mechanisms such as “dry‐get‐drier, wet‐get‐wetter”; “rich‐get‐richer”; or “upped‐ante” focus on the spatial pattern of rainfall changes rather than the changes in probability distribution. Here, we present a quantitative explanation of the warming‐induced probability distribution change of rainfall: Subcloud moist static energy (MSE) gradients are amplified by Clausius‐Clapeyron relationship given roughly uniform warming and constant relative humidity. Therefore, the present‐day wet regions will become more competitive for convection in a warmer world. Though changes in the atmospheric circulation pattern can enhance rainfall in one place and suppress rainfall in another, our results show that the total effect should be a decrease in the area of active convection even with uniform warming.

Observing Possible Thermodynamic Controls on Tropical Marine Rainfall in Moist Environments

Abstract Radar and rawinsonde data from four ground-based observing stations in the tropical Indo-Pacific warm pool were used to identify possible associations of environmental state variables and their vertical profiles with radar-derived rain rate inside a mesoscale radar domain when the column-integrated relative humidity (CRH) exceeds 80%. At CRH exceeding 80%, a wide range—from near 0 to ~50 mm day−1—in rain rate is observed; therefore, tropospheric moisture was a necessary but insufficient condition for deep convection. This study seeks to identify possible factors that inhibit rainfall when the atmosphere is sufficiently moist to support large precipitation rates. The domain-mean rain rate was highly sensitive to the areal coverage of intense, convective rainfall that occurs. There were two fundamentally different instances in which convective area was low. One was when the radar domain is primarily occupied by weakly precipitating, stratiform echoes. The other was when the radar domain contained almost no precipitating echoes of any type. While the former was dependent upon the stage of the convective life cycle seen by radar, the latter was probably dependent upon the convective environment. Areal coverage of convective echoes was largely determined by the number of individual convective echoes rather than their sizes, so changes in the clear-air environment of updrafts might have governed how many updrafts grew into deep cumulonimbi. The most likely environmental influence on convective rainfall identified using rawinsonde data was 900–700-hPa lapse rate; however, processes occurring on spatial scales smaller than a radar domain were probably also important but not investigated.

A Lagrangian convective transport scheme including a simulation of the time air parcels spend in updrafts (LaConTra v1.0)

Abstract. We present a Lagrangian convective transport scheme developed for global chemistry and transport models, which considers the variable residence time that an air parcel spends in convection. This is particularly important for accurately simulating the tropospheric chemistry of short-lived species, e.g., for determining the time available for heterogeneous chemical processes on the surface of cloud droplets. In current Lagrangian convective transport schemes air parcels are stochastically redistributed within a fixed time step according to estimated probabilities for convective entrainment as well as the altitude of detrainment. We introduce a new scheme that extends this approach by modeling the variable time that an air parcel spends in convection by estimating vertical updraft velocities. Vertical updraft velocities are obtained by combining convective mass fluxes from meteorological analysis data with a parameterization of convective area fraction profiles. We implement two different parameterizations: a parameterization using an observed constant convective area fraction profile and a parameterization that uses randomly drawn profiles to allow for variability. Our scheme is driven by convective mass fluxes and detrainment rates that originate from an external convective parameterization, which can be obtained from meteorological analysis data or from general circulation models. We study the effect of allowing for a variable time that an air parcel spends in convection by performing simulations in which our scheme is implemented into the trajectory module of the ATLAS chemistry and transport model and is driven by the ECMWF ERA-Interim reanalysis data. In particular, we show that the redistribution of air parcels in our scheme conserves the vertical mass distribution and that the scheme is able to reproduce the convective mass fluxes and detrainment rates of ERA-Interim. We further show that the estimated vertical updraft velocities of our scheme are able to reproduce wind profiler measurements performed in Darwin, Australia, for velocities larger than 0.6 m s−1. SO2 is used as an example to show that there is a significant effect on species mixing ratios when modeling the time spent in convective updrafts compared to a redistribution of air parcels in a fixed time step. Furthermore, we perform long-time global trajectory simulations of radon-222 and compare with aircraft measurements of radon activity.