scholarly journals Interactions between Shallow and Deep Convection under a Finite Departure from Convective Quasi Equilibrium

2012 ◽  
Vol 69 (12) ◽  
pp. 3463-3470 ◽  
Author(s):  
Jun-Ichi Yano ◽  
Robert Plant
Keyword(s):  
Large Scale ◽  
Numerical Models ◽  
Deep Convection ◽  
Present Theory ◽  
Convective System ◽  
Quasi Equilibrium ◽  
Shallow Convection ◽  
Convective Clouds ◽  
Flux Parameterization ◽  
Stable Periodic

Abstract The present paper presents a simple theory for the transformation of nonprecipitating, shallow convection into precipitating, deep convective clouds. To make the pertinent point a much idealized system is considered, consisting only of shallow and deep convection without large-scale forcing. The transformation is described by an explicit coupling between these two types of convection. Shallow convection moistens and cools the atmosphere, whereas deep convection dries and warms the atmosphere, leading to destabilization and stabilization, respectively. Consequently, in their own stand-alone modes, shallow convection perpetually grows, whereas deep convection simply damps: the former never reaches equilibrium, and the latter is never spontaneously generated. Coupling the modes together is the only way to reconcile these undesirable separate tendencies, so that the convective system as a whole can remain in a stable periodic state under this idealized setting. Such coupling is a key missing element in current global atmospheric models. The energy cycle description used herein is fully consistent with the original formulation by Arakawa and Schubert, and is suitable for direct implementation into models using a mass flux parameterization. The coupling would alleviate current problems with the representation of these two types of convection in numerical models. The present theory also provides a pertinent framework for analyzing large-eddy simulations and cloud-resolving modeling.

scholarly journals Observation of Moisture Tendencies Related to Shallow Convection

2015 ◽  
Vol 72 (2) ◽  
pp. 641-659 ◽  
Author(s):  
H. Bellenger ◽  
K. Yoneyama ◽  
M. Katsumata ◽  
T. Nishizawa ◽  
K. Yasunaga ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
Numerical Models ◽  
Global Climate ◽  
Intraseasonal Variability ◽  
Lower Troposphere ◽  
Shallow Convection ◽  
Initial Attempt ◽  
Convective Clouds ◽  
Key Factor

Abstract Tropospheric moisture is a key factor controlling the global climate and its variability. For instance, moistening of the lower troposphere is necessary to trigger the convective phase of a Madden–Julian oscillation (MJO). However, the relative importance of the processes controlling this moistening has yet to be quantified. Among these processes, the importance of the moistening by shallow convection is still debated. The authors use high-frequency observations of humidity and convection from the Research Vessel (R/V) Mirai that was located in the Indian Ocean ITCZ during the Cooperative Indian Ocean Experiment on Intraseasonal Variability/Dynamics of the MJO (CINDY/DYNAMO) campaign. This study is an initial attempt to directly link shallow convection to moisture variations within the lowest 4 km of the atmosphere from the convective scale to the mesoscale. Within a few tens of minutes and near shallow convection occurrences, moisture anomalies of 0.25–0.5 g kg−1 that correspond to tendencies on the order of 10–20 g kg−1 day−1 between 1 and 4 km are observed and are attributed to shallow convective clouds. On the scale of a few hours, shallow convection is associated with anomalies of 0.5–1 g kg−1 that correspond to tendencies on the order of 1–4 g kg−1 day−1 according to two independent datasets: lidar and soundings. This can be interpreted as the resultant mesoscale effect of the population of shallow convective clouds. Large-scale advective tendencies can be stronger than the moistening by shallow convection; however, the latter is a steady moisture supply whose importance can increase with the time scale. This evaluation of the moistening tendency related to shallow convection is ultimately important to develop and constrain numerical models.

scholarly journals Mesoscale Features Associated with Tropical Cyclone Formations in the Western North Pacific

2008 ◽  
Vol 136 (6) ◽  
pp. 2006-2022 ◽  
Author(s):  
Cheng-Shang Lee ◽  
Kevin K. W. Cheung ◽  
Jenny S. N. Hui ◽  
Russell L. Elsberry
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
North Pacific Ocean ◽  
Deep Convection ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Synoptic Patterns ◽  
The Mean

Abstract The mesoscale features of 124 tropical cyclone formations in the western North Pacific Ocean during 1999–2004 are investigated through large-scale analyses, satellite infrared brightness temperature (TB), and Quick Scatterometer (QuikSCAT) oceanic wind data. Based on low-level wind flow and surge direction, the formation cases are classified into six synoptic patterns: easterly wave (EW), northeasterly flow (NE), coexistence of northeasterly and southwesterly flow (NE–SW), southwesterly flow (SW), monsoon confluence (MC), and monsoon shear (MS). Then the general convection characteristics and mesoscale convective system (MCS) activities associated with these formation cases are studied under this classification scheme. Convection processes in the EW cases are distinguished from the monsoon-related formations in that the convection is less deep and closer to the formation center. Five characteristic temporal evolutions of the deep convection are identified: (i) single convection event, (ii) two convection events, (iii) three convection events, (iv) gradual decrease in TB, and (v) fluctuating TB, or a slight increase in TB before formation. Although no dominant temporal evolution differentiates cases in the six synoptic patterns, evolutions ii and iii seem to be the common routes taken by the monsoon-related formations. The overall percentage of cases with MCS activity at multiple times is 63%, and in 35% of cases more than one MCS coexisted. Most of the MC and MS cases develop multiple MCSs that lead to several episodes of deep convection. These two patterns have the highest percentage of coexisting MCSs such that potential interaction between these systems may play a role in the formation process. The MCSs in the monsoon-related formations are distributed around the center, except in the NE–SW cases in which clustering of MCSs is found about 100–200 km east of the center during the 12 h before formation. On average only one MCS occurs during an EW formation, whereas the mean value is around two for the other monsoon-related patterns. Both the mean lifetime and time of first appearance of MCS in EW are much shorter than those developed in other synoptic patterns, which indicates that the overall formation evolution in the EW case is faster. Moreover, this MCS is most likely to be found within 100 km east of the center 12 h before formation. The implications of these results to internal mechanisms of tropical cyclone formation are discussed in light of other recent mesoscale studies.

Aerosol effects on shallow cumulus cloud fields in idealised and realistic simulations

2020 ◽  
Author(s):  
George Spill ◽  
Philip Stier ◽  
Paul Field ◽  
Guy Dagan
Keyword(s):  
Large Scale ◽  
Trade Wind ◽  
Quasi Equilibrium ◽  
Cumulus Cloud ◽  
Shallow Convection ◽  
Shallow Cumulus ◽  
Synoptic Conditions ◽  
Large Eddy ◽  
Transient Forcing ◽  
Periodic Domains

<p>Shallow cumulus clouds interact with their environment in myriad significant ways, and yet their behavour is still poorly understood, and is responsible for much uncertainty in climate models. Improving our understanding of these clouds is therefore an important part of improving our understanding of the climate system as a whole.</p><p>Modelling studies of shallow convection have traditionally made use of highly idealised simulations using large-eddy models, which allow for high resolution, detailed simulations. However, this idealised nature, with periodic boundaries and constant forcing, and the quasi-equilibrium cloud fields produced, means that they do not capture the effect of transient forcing and conditions found in the real atmosphere, which contains shallow cumulus cloud fields unlikely to be in equilibrium.<span> </span></p><p>Simulations with more realistic nested domains and forcings have previously been shown to have significant persistent responses differently to aerosol perturbations, in contrast to many large eddy simulations in which perturbed runs tend to reach a similar quasi-equilibrium.<span> </span></p><p>Here, we further this investigation by using a single model to present a comparison of familiar idealised simulations of trade wind cumuli in periodic domains, and simulations with a nested domain, whose boundary conditions are provided by a global driving model, able to simulate transient synoptic conditions.<span> </span></p><p>The simulations are carried out using the Met Office Unified Model (UM), and are based on a case study from the Rain In Cumulus over the Ocean (RICO) field campaign. Large domains of 500km are chosen in order to capture large scale cloud field behaviour. A double-moment interactive microphysics scheme is used, along with prescribed aerosol profiles based on RICO observations, which are then perturbed.</p><p>We find that the choice between realistic nested domains with transient forcing and idealised periodic domains with constant forcing does indeed affect the nature of the response to aerosol perturbations, with the realistic simulations displaying much larger persistent changes in domain mean fields such as liquid water path and precipitation rate.<span> </span></p>

Diurnal Cycle of Shallow and Deep Convection for a Tropical Land and an Ocean Environment and Its Relationship to Synoptic Wind Regimes

2006 ◽  
Vol 134 (10) ◽  
pp. 2688-2701 ◽  
Author(s):  
L. Gustavo Pereira ◽  
Steven A. Rutledge
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
Field Experiments ◽  
Deep Convection ◽  
Shallow Convection ◽  
Wind Regime ◽  
Diurnal Variability ◽  
Synoptic Wind ◽  
Wind Regimes ◽  
Rain Rates

Abstract The characteristics of shallow and deep convection during the Tropical Rainfall Measuring Mission/Large-Scale Biosphere–Atmosphere Experiment in Amazonia (TRMM/LBA) and the Eastern Pacific Investigation of Climate Processes in the Coupled Ocean–Atmosphere System (EPIC) are evaluated in this study. Using high-quality radar data collected during these two tropical field experiments, the reflectivity profiles, rain rates, fraction of convective area, and fraction of rainfall volume in each region are examined. This study focuses on the diurnal cycle of shallow and deep convection for the identified wind regimes in both regions. The easterly phase in TRMM/LBA and the northerly wind regime in EPIC were associated with the strongest convection, indicated by larger rain rates, higher reflectivities, and deeper convective cores compared to the westerly phase in TRMM/LBA and the southerly regime in EPIC. The diurnal cycle results indicated that convection initiates in the morning and peaks in the afternoon during TRMM/LBA, whereas in the east Pacific the diurnal cycle of convection is very dependent on the wind regime. Deep convection in the northerly regime peaks around midnight, nearly 6 h before its southerly regime counterpart. Moreover, the northerly regime of EPIC was dominated by convective rainfall, whereas the southerly regime was dominated by stratiform rainfall. The diurnal variability was more pronounced during TRMM/LBA than in EPIC. Shallow convection was associated with 10% and 3% of precipitation during TRMM/LBA and EPIC, respectively.

scholarly journals Why Does Arakawa and Schubert’s Convective Quasi-Equilibrium Closure Not Work? Mathematical Analysis and Implications

2020 ◽  
Vol 77 (4) ◽  
pp. 1371-1385 ◽  
Author(s):  
Jun-Ichi Yano ◽  
Robert S. Plant
Keyword(s):  
Large Scale ◽  
Original Form ◽  
Quasi Equilibrium ◽  
Shallow Convection ◽  
Interaction Kernel ◽  
Guiding Principle ◽  
Mass Fluxes ◽  
Vector Decomposition ◽  
Stratiform Clouds ◽  
Convection Parameterization

Abstract Arakawa and Schubert proposed convective quasi equilibrium as a guiding principle for the closure of convection parameterization. However, empirical experiences from operational implementation efforts suggest that its strict application does not work well. The purpose of the present paper is to explain mathematically why this closure does not work in practice, and to suggest that problems stem from physically unrealistic assumptions. For this purpose, the closure hypothesis is examined in its original form, and without imposing a condition of a positiveness to the convective mass fluxes. The Jordan sounding with idealized large-scale forcing is used for diagnosis purposes. The question is addressed from several perspectives including the completeness of the entraining-plume spectrum, and a singular vector decomposition of the interaction kernel matrix. The main problems with the quasi-equilibrium closure are traced to (i) the relatively slow response of shallower convective modes to large-scale forcing and (ii) detrainment at convection top producing strong cooling and moistening. A strict application of the convective quasi-equilibrium principle leads to a singular response of shallow convection. An explicit coupling of convection with stratiform clouds would be crucial for preventing this unrealistic behavior, recognizing that the reevaporation of detrained cloudy air is a relatively slow process.

Comparison Studies of Cloud- and Convection-Related Processes Simulated by the Canadian Regional Climate Model over the Pacific Ocean

2008 ◽  
Vol 136 (11) ◽  
pp. 4168-4187 ◽  
Author(s):  
Yanjun Jiao ◽  
Colin Jones
Keyword(s):  
Boundary Layer ◽  
Cross Section ◽  
Cloud Cover ◽  
Large Scale ◽  
Climate Model ◽  
Deep Convection ◽  
Regional Climate ◽  
Eddy Diffusivity ◽  
Shallow Convection ◽  
The Tropical Pacific

Abstract This paper presents results from the Canadian Regional Climate Model (CRCM) contribution to the Global Energy and Water Cycle Experiment (GEWEX) Pacific Cross-section Intercomparison Project. This experiment constitutes a simulation of stratocumulus, trade cumulus, and deep convective transitions along a cross section in the tropical Pacific. The simulated seasonal mean cloud and convection are compared between an original version of CRCM (CRCM4) and a modified version (CRCMM) with refined parameterizations. Results are further compared against available observations and reanalysis data. The specific parameterization refinements touch upon the triggering and closure of shallow convection, the cloud and updraft characteristics of deep convection, the parameterization of large-scale cloud fraction, the calculation of the eddy diffusivity in the boundary layer, and the evaporation of falling large-scale precipitation. CRCMM shows substantial improvement in many aspects of the simulated seasonal mean cloud, convection, and precipitation over the tropical Pacific, CRCMM-simulated total column water vapor, total cloud cover, and precipitation are in better agreement with observations than in the original CRCM4 model. The maximum frequency of the shallow convection shifts from the ITCZ region in CRCM4 to the subtropics in CRCMM; accordingly, excessive cloud in the shallow cumulus region in CRCM4 is greatly diminished. Finally, CRCMM better simulates the vertical structure of relative humidity, cloud cover, and vertical velocity, at least when compared to the 40-yr ECMWF Re-Analysis. Analyses of sensitivity experiments assessing specific effects of individual parameterization changes indicate that the modification to the eddy diffusivity in the boundary layer and changes to deep convection contribute most significantly to the overall model improvements.

scholarly journals A modified lightning potential index for numerical models with parameterized deep convection

2021 ◽  
Author(s):  
Guido Schröder
Keyword(s):  
Central Europe ◽  
Vertical Velocity ◽  
Large Scale ◽  
Numerical Models ◽  
Deep Convection ◽  
Potential Temperature ◽  
Wrf Model ◽  
Lightning Flash ◽  
Potential Index ◽  
Forecasting System

<p>A modified lightning potential index (MLPI) for numerical models with parameterized deep convection is presented. It is based on the LPI formula of Lynn and Yair (2010). Following the idea of Lopez (2016), the quantities (e.g. vertical velocity) needed in the LPI formula are derived from the updraft of the Bechtold-Tiedtke parameterization scheme (Bechtold et al., 2014). The formula is further improved by taking into account the vertical equivalent potential temperature gradient.</p><p>The LPI and MLPI are tested in ICON with 20km resolution (ICON-20) over central Europe. A key component in the LPI is the vertical velocity. To assess its quality, the vertical velocity of the updraft in the convection scheme in ICON-20 is compared to updrafts in the convection-resolving COSMO model with 2.2 km resolution (COSMO-D2). It is shown that in ICON-20 the extension of the vertical velocity is generally broader with the maximum located in higher altitudes. In the charge separation area where the vertical velocity is relevant, the ICON-20 vertical velocity is less than in COSMO-D2. Consequently, the LPI values in ICON-20 are lower by a factor of 2 compared to COSMO-D2.</p><p>The MLPI is verified against LINET lightning data (Betz et al. 2009) over central Europe for summer 2020 and compared to LPI in COSMO-D2. The MLPI is also compared to the LPI and the lightning flash density (LFD,  Lopez, 2016), all computed in ICON-20. For the test period the MLPI outperforms the LPI and LFD. However, the quality of the LPI in COSMO-D2 cannot quite be reached.</p><p> </p><p>Bechtold et al. 2014: Representing Equilibrium and Nonequilibrium Convection in Large-Scale Models. J. Atmos. Sci. 71, 734-753.</p><p>Betz et al., 2009:  LINET - An international lightning detection network in Europe. Atmos.  Res. 91 564–573.</p><p>Lopez, 2016: A Lightning Parameterization for the ECMWF Integrated Forecasting System. Mon. Wea. Rev., 144, 3057-2075.</p><p>Lynn and Yair, 2010: Prediction of lightning flash density with the WRF model  Adv. Geosci., 23, 11–16.</p>

scholarly journals Convective self–aggregation in a mean flow

2020 ◽  
Author(s):  
Hyunju Jung ◽  
Ann Kristin Naumann ◽  
Bjorn Stevens
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Surface Flux ◽  
Horizontal Wind ◽  
Convective System ◽  
Mean Flow ◽  
Near Surface ◽  
Tropical Deep Convection ◽  
Large Scale Flow ◽  
Self Aggregation

Abstract. Convective self-aggregation is an atmospheric phenomenon found in numerical simulations in a radiative convective equilibrium framework of which configuration captures the main characteristics of the real-world convection in the deep tropics. As tropical deep convection is typically embedded in a large-scale flow, we impose a background mean wind flow on convection-permitting simulations through the surface flux calculation. The simulations show that with imposing mean flow, the organized convective system propagates in the direction of the flow but slows down compared to what pure advection would suggest, and eventually becomes stationary relative to the surface after 15 simulation days. The termination of the propagation arises from momentum flux, which acts as a drag on the near-surface horizontal wind. In contrast, the thermodynamic response through the wind-induced surface heat exchange feedback is a relatively small effect, which slightly retards (by about 15 %) the convection relative to the mean wind.

Impact of the Korea Rapid Developing Thunderstorms (K-RDT) product nudging to the convective parameterization over the Korean Peninsula

2020 ◽  
Author(s):  
Namgu Yeo ◽  
Eun-Chul Chang ◽  
Ki-Hong Min
Keyword(s):  
Heavy Rainfall ◽  
Large Scale ◽  
Deep Convection ◽  
Weather Prediction ◽  
Model System ◽  
Prediction Skill ◽  
Precipitation Forecast ◽  
Small Scale ◽  
Convective System ◽  
Convective Cells

<p>In this study, Korea Rapid Developing Thunderstorms (K-RDT) product from geostationary meteorological satellite which represents developing stage of convective cells is nudged to the Simplified Arakawa Schubert (SAS) deep convection scheme using a simple nudging technique in order to improve prediction skill of a heavy rainfall caused by mesoscale convective system over South Korea in the short-term forecast. Impact of the K-RDT information is investigated on the Global/Regional Integrated Model system (GRIMs) regional model program (RMP) system. For the selected heavy rainfall cases, the control run without nudging and two nudging experiments with different nudging period are performed. Although the simulated precipitations in the nudging experiments tend to depend on the distribution of convective cells detected in the K-RDT algorithm, the nudging experiment shows improved precipitation forecast than the control experiment. Particularly, the experiment with nudging for longer time produces better prediction skill. The results present that the small-scale convective cells from the K-RDT which are detected with a 1-km resolution have clear impacts to large-scale atmospheric fields. Therefore, it is suggested that utilizing small-scale information of convective system in the numerical weather prediction can have critical impact to improve forecast skill when the model system, which cannot properly represent sub-grid scale convections.</p>

scholarly journals Boundary Layer Quasi-Equilibrium Limits Convective Intensity Enhancement from the Diurnal Cycle in Surface Heating

2019 ◽  
Vol 77 (1) ◽  
pp. 217-237
Author(s):  
Zachary R. Hansen ◽  
Larissa E. Back ◽  
Peigen Zhou
Keyword(s):  
Boundary Layer ◽  
Diurnal Cycle ◽  
Large Scale ◽  
Deep Convection ◽  
Reanalysis Data ◽  
Surface Fluxes ◽  
Quasi Equilibrium ◽  
The Impact ◽  
Precipitation Enhancement ◽  
High Percentile

Abstract A combination of cloud-permitting model (CPM) simulations, satellite, and reanalysis data are used to test whether the diurnal cycle in surface temperature has a significant impact on the intensity of deep convection as measured by high-percentile updraft velocities, lightning, and CAPE. The land–ocean contrast in lightning activity shows that convective intensity varies between land and ocean independently from convective quantity. Thus, a mechanism that explains the land–ocean contrast must be able to do so even after controlling for precipitation variations. Motivated by the land–ocean contrast, we use idealized CPM simulations to test the impact of the diurnal cycle on high-percentile updrafts. In simulations, updrafts are somewhat enhanced due to large-scale precipitation enhancement by the diurnal cycle. To control for large-scale precipitation, we use statistical sampling techniques. After controlling for precipitation enhancement, the diurnal cycle does not affect convective intensities. To explain why sampled updrafts are not enhanced, we note that CAPE is also not increased, likely due to boundary layer quasi equilibrium (BLQE) occurring over our land area. Analysis of BLQE in terms of net positive and negative mass flux finds that boundary layer entrainment, and even more importantly downdrafts, account for most of the moist static energy (MSE) sink that is balancing surface fluxes. Using ERA-Interim data, we also find qualitative evidence for BLQE over land in the real world, as high percentiles of CAPE are not greater over land than over ocean.

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