Convective Fraction Research Articles

Fire behavior of mining vehicles in underground hard rock mines

The results from a number of investigations and fire experiments are presented and analyzed in order to characterize the fire behavior of mining vehicles in underground hard rock mines. The analysis also includes fire safety and fire protection measures with respect to the mining vehicle fire behavior. Earlier studies on fires in underground hard rock mines have shown that vehicles or mobile equipment are the dominant sources of fire. A better knowledge about the fire behavior of vehicles in underground hard rock mines is therefore needed. During the analysis the direction and flow rate of the ventilation in a drift was found to have a significant impact on the fire behavior, causing for example flame tilt with rapid fire spread. The shielded sections of a vehicle will be less affected by the ventilation flow resulting in for example a decreased flame spread. It was also found that spray fires may result in considerable heat release rate but are generally of shorter duration and will not make any significant contributions to the overall heat release rate of the fully developed vehicle fire. The fire duration of a loader tire from a full-scale fire experiment was found to be at least 200min and will largely determine the total fire duration of the vehicle. A different scenario with different conditions with for example a slower flame spread resulted in an even longer fire duration. The radiative and convective fraction will be a key factor when determining the heat transfer mechanisms involved in a fire and will vary from material to material. Calculations show that the radiative fraction of the tire fires on two mining vehicles is significantly lower than found in earlier experiments. The design and construction of the mining vehicle will have an important impact on the fire behavior and could possibly mitigate the consequences of a fire and allow fire personnel to extinguish a fire that otherwise would have had a too high heat release rate.

Metrics for the evaluation of warm convective cloud fields in a large‐eddy simulation with Meteosat images

The representation of warm convective clouds in atmospheric models and satellite observations can considerably deviate from each other partly due to different spatial resolutions. This study aims to establish appropriate metrics to evaluate high‐resolution simulations of convective clouds by the ICON Large‐Eddy Model (ICON‐LEM) with observations from Meteosat SEVIRI over Germany. The time series and frequency distributions of convective cloud fraction and liquid water path (LWP) are analyzed. Furthermore, the study focuses on size distributions and decorrelation scales of warm convective cloud fields. The investigated metrics possess a pronounced sensitivity to the apparent spatial resolution. At the fine spatial scale, the simulations show higher occurrence frequencies of large LWP values and a factor of two to four smaller convective cloud fractions. Coarse‐graining of simulated fields to the optical resolution of Meteosat essentially removes the differences between the observed and simulated metrics. The distribution of simulated cloud sizes compares well with the observations and can be represented by a power law, with a moderate resolution sensitivity. A lower limit of cloud sizes is identified, which is 8–10 times the native grid resolution of the model. This likely marks the effective model resolution beyond which the scaling behaviour of considered metrics is not reliable, implying that a further increase in spatial resolution would be desirable to better resolve cloud processes below 1 km. It is finally shown that ICON‐LEM is consistent with spatio‐temporal decorrelation scales observed with Meteosat having values of 30 min and 7 km, if transferred to the true optical satellite resolution. However, the simulated Lagrangian decorrelation times drop to 10 min at 1 km resolution, a scale covered by the upcoming generation of geostationary satellites.

Estimating Vertical Motion Profile Top-Heaviness: Reanalysis Compared to Satellite-Based Observations and Stratiform Rain Fraction

Abstract A method for representing geographic variability in vertical motion profile top-heaviness in reanalysis data is introduced. The results from this method are compared to a satellite-based method for estimating top-heaviness of vertical motion profiles over the oceans. The satellite-based method utilizes basis functions, idealized or from reanalysis, along with scatterometer wind convergence data and rainfall to estimate the top-heaviness of the vertical motion profile. Results from the two methods of estimating top-heaviness are significantly correlated. Both estimates of top-heaviness are compared to stratiform, shallow, and convective rain fraction. Findings show geographic variability in stratiform rain fraction is not well correlated with estimated profile top-heaviness. Shallow rain fraction is not variable enough to explain this finding. The results may be due to geographic variations in the shape of convective or stratiform heating profiles. An example is given of how variations in convective heating profiles could lead to a region with more stratiform rain having a more bottom-heavy profile.

A Mass-Flux Cumulus Parameterization Scheme across Gray-Zone Resolutions

AbstractA method that enables a mass-flux cumulus parameterization scheme (CPS) to work seamlessly in various model grids across CPS gray-zone resolutions is proposed. The convective cloud-base mass flux, convective inhibition, and convective detrainment in the simplified Arakawa–Schubert (SAS) scheme are modified to be functions of the convective updraft fraction. The combination of two updraft fractions is used to modulate the cloud-base mass flux; the first one depends on the horizontal grid space and the other is a function of the grid-scale and convective vertical velocity. The convective inhibition and detrainment of hydrometeors are also modified to be a function of the grid-size-dependent convective updraft fraction.A set of sensitivity experiments with the Weather Research and Forecasting (WRF) Model is conducted for a heavy rainfall case over South Korea. The results show that the revised SAS CPS outperforms the original SAS. At 3 and 1 km, the precipitation core over South Korea is well reproduced by the experiments with the revised SAS scheme. On the contrary, the simulated precipitation is widespread in the case of the original SAS experiment and there are multiple spurious cores when the CPS is removed at those resolutions. The modified mass flux at the cloud base is found to play a major role in organizing the grid-scale precipitation at the convective core. A 1-month simulation at 3 km confirms that the revised scheme produces slightly better summer monsoonal precipitation results as compared to the typical model setup without CPS.

Regional Variability of Rain Clouds in the Amazon Basin as Seen by a Network of Weather Radars

AbstractA new dataset based on 5 yr of operational meteorological weather radars from the Amazon Protection System has enabled new knowledge in relation to rainfall in the Amazon basin. The rainy features are analyzed for 10 different regions in terms of the annual and diurnal cycles of radar reflectivity, as well as the vertical distribution, in addition to lightning data. Similarities between the annual and diurnal cycles are found in the northwestern and western, southwestern and southern, and northeastern and northern Amazon. Nocturnal peaks are found in stratiform fraction in the southern, southwestern, western, northwestern, northern, central western, and coastal regions. The convective fractions in the western, northwestern, northern, and central eastern regions also show nocturnal peaks. The radar reflectivity vertical distributions analysis indicates that in the northern coast close to Belém, heavy rainfall with deep convective systems is observed throughout the year, while heavy rainfall in the central Amazon close to Manaus, Tefé, and Santarém occurs in the dry season. More oceanic-like clouds are also observed there and in other locations on the northern coast like Macapá, where the frequency of lightning is quite low. São Gabriel da Cachoeira, located in the northwest portion of the Amazon basin, has a regime with rainfall in all seasons with a slight decrease from August to October when the systems become more convective and have more lightning.

Convective cloud vertical velocity and mass‐flux characteristics from radar wind profiler observations during GoAmazon2014/5

AbstractA radar wind profiler data set collected during the 2 year Department of Energy Atmospheric Radiation Measurement Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) campaign is used to estimate convective cloud vertical velocity, area fraction, and mass flux profiles. Vertical velocity observations are presented using cumulative frequency histograms and weighted mean profiles to provide insights in a manner suitable for global climate model scale comparisons (spatial domains from 20 km to 60 km). Convective profile sensitivity to changes in environmental conditions and seasonal regime controls is also considered. Aggregate and ensemble average vertical velocity, convective area fraction, and mass flux profiles, as well as magnitudes and relative profile behaviors, are found consistent with previous studies. Updrafts and downdrafts increase in magnitude with height to midlevels (6 to 10 km), with updraft area also increasing with height. Updraft mass flux profiles similarly increase with height, showing a peak in magnitude near 8 km. Downdrafts are observed to be most frequent below the freezing level, with downdraft area monotonically decreasing with height. Updraft and downdraft profile behaviors are further stratified according to environmental controls. These results indicate stronger vertical velocity profile behaviors under higher convective available potential energy and lower low‐level moisture conditions. Sharp contrasts in convective area fraction and mass flux profiles are most pronounced when retrievals are segregated according to Amazonian wet and dry season conditions. During this deployment, wet season regimes favored higher domain mass flux profiles, attributed to more frequent convection that offsets weaker average convective cell vertical velocities.

More frequent showers and thunderstorm days under a warming climate: evidence observed over Northern Eurasia from 1966 to 2000

This study uses 3-hourly synoptic observations at 547 stations to examine changes in convective and non-convective precipitation days and their associations with surface air temperature and specific humidity over Northern Eurasia. We found that convective days (showers and those associated with thunder and lightning) have become more frequent possibly at the expense of non-convective ones for all seasons during the study period of 1966–2000. The mean trends for convective day fraction (total convective precipitation events divided by all precipitation events for each season) are very similar among all four seasons at around 0.61–0.76% per year averaged over the study region. The temperature and humidity associated with convective events are on average 2.4–5.6 °C and 0.4–0.9 g/kg higher than those of non-convective events, respectively. This study suggests that surface warming and moistening lead to increased tropospheric static instability, contributing to the observed trends.

Aerosols and lightning activity: The effect of vertical profile and aerosol type

The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument on board the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite has been utilized for the first time in a study regarding lightning activity modulation due to aerosols. Lightning activity observations, obtained by the ZEUS long range Lightning Detection Network, European Centre for Medium range Weather Forecasts (ECMWF) Convective Available Potential Energy (CAPE) data and Cloud Fraction (CF) retrieved by MODIS on board Aqua satellite have been combined with CALIPSO CALIOP data over the Mediterranean basin and for the period March to November, from 2007 to 2014. The results indicate that lightning activity is enhanced during days characterized by higher Aerosol Optical Depth (AOD) values, compared to days with no lightning. This study contributes to existing studies on the link between lightning activity and aerosols, which have been based just on columnar AOD satellite retrievals, by performing a deeper analysis into the effect of aerosol profiles and aerosol types. Correlation coefficients of R=0.73 between the CALIPSO AOD and the number of lightning strikes detected by ZEUS and of R=0.93 between ECMWF CAPE and lightning activity are obtained. The analysis of extinction coefficient values at 532nm indicates that at an altitudinal range exists, between 1.1km and 2.9km, where the values for extinction coefficient of lightning-active and non-lightning-active cases are statistically significantly different. Finally, based on the CALIPSO aerosol subtype classification, we have investigated the aerosol conditions of lightning-active and non-lightning-active cases. According to the results polluted dust aerosols are more frequently observed during non-lightning-active days, while dust and smoke aerosols are more abundant in the atmosphere during the lightning-active days.

Effect of the ambient pressure on the heat release rates of n-heptane pool fires

To investigate the influence of low air pressure on the heat release rate, two groups of the configured experiments on n-heptane pool fires were conducted with burners of three sizes (D = 0.3, 0.35, 0.4 m) in Hefei (99.8 kPa) and Lhasa (66.5 kPa), respectively. The unified standard calculation method confirmed in ISO 9705 was adjusted by introducing the effect of the ambient air pressure. The experimental results indicate that the effect of pressure on the burning rate seems very weak in the case of the thin layer pool fires. However, the heat release rates increase a little at the higher altitude, which may be due to the less soot yield under the lower pressure. The combustion efficiency X a and the convective heat fraction X c rises a little with the decreasing pressure, while the radiative fraction X r shows independent on pressure. The smoke temperature is a little higher at the higher altitude due to the stretching flame.

Analyzing the Grell–Freitas Convection Scheme from Hydrostatic to Nonhydrostatic Scales within a Global Model

Abstract The authors implemented the Grell–Freitas (GF) parameterization of convection in which the cloud-base mass flux varies quadratically as a function of the convective updraft fraction in the global nonhydrostatic Model for Prediction Across Scales (MPAS). They evaluated the performance of GF using quasi-uniform meshes and a variable-resolution mesh centered over South America, the resolution of which varied between hydrostatic (50 km) and nonhydrostatic (3 km) scales. Four-day forecasts using a 50-km and a 15-km quasi-uniform mesh, initialized with GFS data for 0000 UTC 10 January 2014, reveal that MPAS overestimates precipitation in the tropics relative to the Tropical Rainfall Measuring Mission Multisatellite Precipitation Analysis data. Results of 4-day forecasts using the variable-resolution mesh reveal that over the refined region of the mesh, GF performs as a precipitating shallow convective scheme, whereas over the coarse region of the mesh, GF acts as a conventional deep convective scheme. As horizontal resolution increases and subgrid-scale motions become increasingly resolved, the contribution of convective and grid-scale precipitation to the total precipitation decreases and increases, respectively. Probability density distributions of precipitation highlight a smooth transition in the partitioning between convective and grid-scale precipitation, including at gray-zone scales across the transition region between the coarsest and finest regions of the global mesh. Variable-resolution meshes spanning between hydrostatic and nonhydrostatic scales are shown to be ideal tools to evaluate the horizontal scale dependence of parameterized convective and grid-scale moist processes.

Non-local convergence coupling in a simple stochastic convection model

Observational studies show a strong correlation between large-scale wind convergence and precipitation. However, using this as a convective closure assumption to determine the total precipitation in a numerical model typically leads to deleterious wave-CISK behavior such as grid-scale noise. The quasi-equilibrium (QE) schemes ameliorate this issue and smooth the precipitation field, but still inadequately represent the intermittent and organized nature of tropical convection. However, recent observational evidence highlights that the large-scale convergence field primarily affects precipitation by increasing the overall convective cloud fraction rather than the energetics of individual convective elements. In this article, the dynamical consequences of this diagnostic observation are studied using a simple one baroclinic mode stochastic model for convectively coupled waves. A version of this model is implemented which couples the stochastic formation of convective elements to the wind convergence. Linearized analysis shows that using the local convergence results in a classic wave-CISK standing instability where the growth rate increases with the wavenumber. However, using a large-scale averaged convergence restricts the instability to physically plausible scales. Convergence coupling is interpreted as a surrogate for the non-local effects of gregarious convection. In nonlinear stochastic simulations with a non-uniform imposed sea surface temperature (SST) field, the non-local convergence coupling introduces desirable intermittent variability on intraseasonal time scales. Convergence coupling leads to a circulation with a similar mean but higher variability than the equivalent parameterization without convergence coupling. Finally, the model is shown to retain these features on fine and coarse mesh sizes.

Stochastic Convection Parameterization with Markov Chains in an Intermediate-Complexity GCM

Abstract Conditional Markov chain (CMC) models have proven to be promising building blocks for stochastic convection parameterizations. In this paper, it is demonstrated how two different CMC models can be used as mass flux closures in convection parameterizations. More specifically, the CMC models provide a stochastic estimate of the convective area fraction that is directly proportional to the cloud-base mass flux. Since, in one of the models, the number of CMCs decreases with increasing resolution, this approach makes convection parameterizations scale aware and introduces stochastic fluctuations that increase with resolution in a realistic way. Both CMC models are implemented in a GCM of intermediate complexity. It is shown that with the CMC models, trained with observational data, it is possible to improve both the subgrid-scale variability and the autocorrelation function of the cloud-base mass flux as well as the distribution of the daily accumulated precipitation in the tropics. Hovmöller diagrams and wavenumber–frequency diagrams of the equatorial precipitation indicate that, in this specific GCM, convectively coupled equatorial waves are more sensitive to the mean cloud-base mass flux than to stochastic fluctuations. A smaller mean mass flux tends to increase the power of the simulated MJO and to diminish equatorial Kelvin waves.

Subgrid‐scale cloud–radiation feedback for theBetts–Miller–Janjić convection scheme

Cloud–radiation feedbacks play a crucial role in the climate system and continue to be a major source of uncertainty in global climate model projections. Despite its importance for regional and local circulations, these feedback processes are not included in subgrid‐scale convective parametrizations used in regional weather and climate models, in particular in adjustment schemes that, as opposed to mass‐flux schemes, do not deal with convective condensates. Here we present a cloud scheme developed for theBetts–Miller–Janjić (BMJ) cumulus scheme used in theWeatherResearch andForecasting (WRF) model that is fully general and can easily be applied to any other convective scheme. We parametrize the convective cloud fraction as a function of theBMJtime‐step precipitation rate with the vertical cloud profile given by a ‘top‐heavy’Poisson distribution, similar to observed profiles. The cloud condensates are defined based on the assumption that the mass of convective cloud per unit mass of water vapour in cloudy air is constant in the column. In this scheme there are two tunable parameters:δ, that determines the vertical structure of the convective cloud, andγ, that controls the amount of cloud mass. The performance of the scheme is evaluated in a 1‐year run andWRFis found to give a much better representation of the observed cloudiness with smaller biases in the surface radiation fields with respect to observations and reanalysis.

On the Mass-Flux Representation of Vertical Transport in Moist Convection

Abstract This study investigates to what extent the convective fluxes formulated within the mass-flux framework can represent the total vertical transport of heat and moisture in the cloud layer and whether the same approach can be extended to represent the vertical momentum transport using large-eddy simulations (LESs) of six well-documented cloud cases, including both deep and shallow convection. Two methods are used to decompose the LES-resolved vertical fluxes: decompositions based on the coherent convective features using the mass-flux top-hat profile and by two-dimensional fast Fourier transform (2D-FFT) in terms of wavenumbers. The analyses show that the convective fluxes computed using the mass-flux formula can account for most of the total fluxes of conservative thermodynamic variables in the cloud layer of both deep and shallow convection for an appropriately defined convective updraft fraction, a result consistent with the mass-flux dynamic view of moist convection and previous studies. However, the mass-flux approach fails to represent the vertical momentum transport in the cloud layer of both deep and shallow convection. The 2D-FFT and other analyses suggest that such a failure results from a number of reasons: 1) the complicated momentum distribution in the cloud layer cannot be well described by the simple top-hat profile; 2) shear-driven small-scale eddies are more efficient momentum carriers than coherent convective plumes; 3) the phase relationship between vertical velocity and horizontal momentum components is substantially different from that between vertical velocity and conservative thermodynamic variables; and 4) the structure of horizontal momentum can change substantially from case to case even in the same climate regime.

Drop Size Distributions and Radar Observations of Convective and Stratiform Rain over the Equatorial Indian and West Pacific Oceans

Abstract Two-dimensional video disdrometer (2DVD) data were analyzed from two equatorial Indian (Gan) and west Pacific Ocean (Manus) islands where precipitation is primarily organized by the intertropical convergence zone and the Madden–Julian oscillation (MJO). The 18 (3.5) months of 2DVD data from Manus (Gan) Island show that 1) the two sites have similar drop size distribution (DSD) spectra of liquid water content, median diameter, rain rate R, radar reflectivity z, normalized gamma number concentration Nw, and other integral rain parameters; 2) there is a robust Nw-based separation between convective (C) and stratiform (S) DSDs at both sites that produces consistent separation in other parameter spaces. The 2DVD data indicate an equatorial, maritime average C/S rainfall accumulation fraction (frequency) of 81/19 (41/59) at these locations. It is hypothesized that convective fraction and frequency estimates are slightly higher than previous radar-based studies, because the ubiquitous weak, shallow convection (<10 mm h−1) characteristic of the tropical warm pool is properly resolved by this high-resolution DSD dataset and identification method. This type of convection accounted for about 30% of all rain events and 15% of total rain volume. These rain statistics were reproduced when newly derived C/S R(z) equations were applied to 2DVD-simulated reflectivity. However, the benefits of using separate C/S R(z) equations are only realizable when C/S partitioning properly classifies each rain type. A single R(z) relationship fit to all 2DVD data yielded accurate total rainfall amounts but overestimated (underestimated) the stratiform (convective) rain fraction by ±10% and overestimated (underestimated) stratiform (convective) rain accumulation by +50% (−15%).

A data‐driven method for the stochastic parametrisation of subgrid‐scale tropical convective area fraction

Observations of tropical convection from precipitation radar and the concurring large‐scale atmospheric state at two locations (Darwin and Kwajalein) are used to establish effective stochastic models to parameterise subgrid‐scale tropical convective activity. Two approaches are presented which rely on the assumption that tropical convection induces a stationary equilibrium distribution. In the first approach we parameterise convection variables such as convective area fraction as an instantaneous random realisation conditioned on the large‐scale vertical velocities according to a probability density function estimated from the observations. In the second approach convection variables are generated in a Markov process conditioned on the large‐scale vertical velocity, allowing for non‐trivial temporal correlations. Despite the different prevalent atmospheric and oceanic regimes at the two locations, with Kwajalein being exposed to a purely oceanic weather regime and Darwin exhibiting land‐sea interaction, we establish that the empirical measure for the convective variables conditioned on large‐scale mid‐level vertical velocities for the two locations are close. This allows us to train the stochastic models at one location and then generate time series of convective activity at the other location. The proposed stochastic subgrid‐scale models adequately reproduce the statistics of the observed convective variables and we discuss how they may be used in future scale‐independent mass‐flux convection parameterisations.

Impact of Amazonian evapotranspiration on moisture transport and convection along the eastern flanks of the tropical Andes

The Weather Research and Forecasting (WRF) model was used to investigate the impact of Amazonian evapotranspiration (ET) on moisture transport and convection along the eastern flanks of the Andes (EADS). To isolate the role of surface ET, quasi‐idealized simulations down to 1.2 km grid spacing were conducted, where over the Amazon lowlands (AMZL) and at every time step the surface sensible‐heat effects are identical to the realistic reference runs while surface latent heat fluxes are prevented from entering the atmosphere. The results show that, without surface ET, daily precipitation within the AMZL decreases by as much as ∼75%, but nearly doubles over the surrounding mountainous regions. This dramatic influence is attributed to a dipole structure of convergence–divergence anomalies over the AMZL, primarily due to the considerable cooling of the troposphere associated with suppressed convection. Further examination of moist static energy evolution indicates that the net decrease in convective available potential energy over the AMZL is due to the removal of surface ET that is only partially compensated by related regional circulation changes. Because of the concave shape of the Andean mountain range, enhanced low‐level divergence promotes air mass accumulation to the east of the central EADS. This perturbation becomes sufficiently strong around nightfall and produces significant eastward low‐level pressure gradient force, rendering stronger winds away from the Andes. Moisture convergence and convection over the EADS vary accordingly, strengthened in the day but attenuated at night. Nocturnal convective motion is, however, more widespread. Analytical solutions of simplified diagnostic equations of convective fraction suggest that reduction of lower troposphere evaporation is the driving mechanism. Additional exploratory experiments with varied surface ET magnitude demonstrate that the connection between the AMZL ET and EADS precipitation is robust.

Relationships between convective structure and transport of aerosols to the upper troposphere deduced from satellite observations

AbstractWe estimate the extent of upper tropospheric aerosol layers (UT ALs) surrounding mesoscale convective systems (MCSs) and explore the relationships between UT AL extent and the morphology, location, and developmental stage of collocated MCSs in the tropics. Our analysis is based on satellite data collected over equatorial Africa, South Asia, and the Amazon basin between June 2006 and June 2008. We identify substantial variations in the relationships between convective properties and aerosol transport by region and stage of convective development. The most extensive UT ALs over equatorial Africa are associated with mature MCSs, while the most extensive UT ALs over South Asia and the Amazon are associated with growing MCSs. Convective aerosol transport over the Amazon is weaker than that observed over the other two regions despite similar transport frequencies, likely due to the smaller sizes and shorter mean lifetimes of MCSs over the Amazon. Variations in UT ALs in the vicinity of tropical MCSs are primarily explained by variations in the horizontal sizes of the associated MCSs and are largely unrelated to aerosol loading in the lower troposphere. We also identify potentially important relationships with the number of convective cores, vertical wind shear, and convective fraction during the growing and mature stages of MCS development. Relationships between convective properties and aerosol transport are relatively weak during the decaying stage of convective development. Our results provide an interpretive framework for devising and evaluating numerical model experiments that examine relationships between convective properties and ALs in the upper troposphere.

Reply to “Comments on ‘A Unified Representation of Deep Moist Convection in Numerical Modeling of the Atmosphere. Part I’”

Arakawa and Wu (2013, hereafter AW13) recently developed a formal approach to a unified parameterization of atmospheric convection for high-resolution numerical models. The work was based on ideas formulated byArakawaetal.(2011)andwasdesignedtoparameterize the eddy transport of moist static energy by convection. AW13 contained two main points: 1) a new formulation for convective transport valid for both small and large convective cloud fractions and 2) a closure in terms of convectivecloudfractionsuitableforsuchsituations.Thus, the key parameter in this approach is convective cloud fraction s. Since only updrafts were considered in AW13, convective cloud fraction was synonymous to updraft fraction. To avoid any confusion, we will use ‘‘updraft fraction’’ exclusively in this note to mean convective cloud fraction in AW13, unless explicitly stated otherwise. In conventional parameterization, it is assumed that s � 1. This assumption is no longer valid when the horizontal resolution of numerical models approaches a few to a few tens of kilometers, since in such situations updraft fraction can be comparable to unity. Therefore, AW13 argue that the conventional approach to formulating an expression for convective transport must include a factor 12s in order to unify the parameterization for the full range of model resolutions so that it is scale aware and valid for large updraft fractions. AW13 raised an important issue in future convective parameterization development. In this note we intend to show that the assumptionofs � 1 was unnecessaryintheconventional approachandthescale-awarenessfactor12s wasalready built in implicitly, although not recognized for the last 40 years. Therefore, the formulation for convective transport in conventional parameterizations should work well even in the gray zone where large updraft fractions exist. To begin, we use the same notation as in AW13 .T o parameterize the vertical transport of moist static energy h by convective updrafts (w 0 h 0 ), we note that any variable c can be written as

Morphology, Intensity, and Rainfall Production of MJO Convection: Observations from DYNAMO Shipborne Radar and TRMM

Abstract This study uses Dynamics of the Madden–Julian Oscillation (DYNAMO) shipborne [Research Vessel (R/V) Roger Revelle] radar and Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) datasets to investigate MJO-associated convective systems in specific organizational modes [mesoscale convective system (MCS) versus sub-MCS and linear versus nonlinear]. The Revelle radar sampled many “climatological” aspects of MJO convection as indicated by comparison with the long-term TRMM PR statistics, including areal-mean rainfall (6–7 mm day−1), convective intensity, rainfall contributions from different morphologies, and their variations with MJO phase. Nonlinear sub-MCSs were present 70% of the time but contributed just around 20% of the total rainfall. In contrast, linear and nonlinear MCSs were present 10% of the time but contributed 20% and 50%, respectively. These distributions vary with MJO phase, with the largest sub-MCS rainfall fraction in suppressed phases (phases 5–7) and maximum MCS precipitation in active phases (phases 2 and 3). Similarly, convective–stratiform rainfall fractions also varied significantly with MJO phase, with the highest convective fractions (70%–80%) in suppressed phases and the largest stratiform fraction (40%–50%) in active phases. However, there are also discrepancies between the Revelle radar and TRMM PR. Revelle radar data indicated a mean convective rain fraction of 70% compared to 55% for TRMM PR. This difference is mainly due to the reduced resolution of the TRMM PR compared to the ship radar. There are also notable differences in the rainfall contributions as a function of convective intensity between the Revelle radar and TRMM PR. In addition, TRMM PR composites indicate linear MCS rainfall increases after MJO onset and produce similar rainfall contributions to nonlinear MCSs; however, the Revelle radar statistics show the clear dominance of nonlinear MCS rainfall.