An Investigation of Hydrometeor Latent Cooling upon Convective Cold Pool Formation, Sustainment, and Properties

2019 ◽  
Vol 147 (9) ◽  
pp. 3205-3222 ◽  
Author(s):  
Holly M. Mallinson ◽  
Sonia G. Lasher-Trapp
Keyword(s):  
Cold Pool ◽  
Convective Activity ◽  
Dominant Term ◽  
Convective Clouds ◽  
Cold Pools ◽  
Warm Rain ◽  
Warm Rain Process ◽  
Microphysical Processes ◽  
Pool Formation ◽  
Melting Level

Abstract Downdrafts extending from convective clouds can produce cold pools that propagate outward, sometimes initiating new convection along their leading edges. Models operating at scales requiring convective parameterizations usually lack representation of this detail, and thus fail to predict this convective regeneration and longer episodes of convective activity. Developing such parameterizations requires an improved understanding of the physical drivers of cold pools, and detailed studies of the roles of all the contributing microphysical processes have been lacking. This study utilizes a set of 12 simulations conducted within a single convective environment, but with variability in the microphysical fields produced by varying parameters influencing warm-rain or ice processes. Time-integrated microphysical budgets quantify the contribution of each hydrometeor type to the total latent cooling occurring in the downdrafts that form and sustain the cold pool. The timing of the onset of the cold pool is earlier in cases with a stronger warm rain process, but both graupel and rain were equally as likely to be the dominant hydrometeor in the downdraft first forming the cold pool. Graupel sublimation is the dominant term in sustaining the cold pool in all simulations, but the evaporation of rain has the strongest correlation to the cold pool expansion rate, depth, and intensity. Reconciling the current results with past studies elucidates the importance of considering: graupel sublimation, the latent cooling only in downdrafts contributing to the cold pool, and latent cooling in those downdrafts at altitudes that may be significantly higher than the melting level.

Impact of Graupel Parameterization Schemes on Idealized Bow Echo Simulations

2013 ◽  
Vol 141 (4) ◽  
pp. 1241-1262 ◽  
Author(s):  
Rebecca D. Adams-Selin ◽  
Susan C. van den Heever ◽  
Richard H. Johnson
Keyword(s):  
Complete Removal ◽  
Cold Pool ◽  
Size Distributions ◽  
Pressure Gradients ◽  
Cooling Rates ◽  
Cold Pools ◽  
Highly Sensitive ◽  
Bow Echo ◽  
Mean Size ◽  
Microphysical Processes

Abstract The effect of changes in microphysical cooling rates on bow echo development and longevity are examined through changes to graupel parameterization in the Advanced Research Weather Research and Forecasting Model (ARW-WRF). Multiple simulations are performed that test the sensitivity to different graupel size distributions as well as the complete removal of graupel. It is found that size distributions with larger and denser, but fewer, graupel hydrometeors result in a weaker cold pool due to reduced microphysical cooling rates. This yields weaker midlevel (3–6 km) buoyancy and pressure perturbations, a later onset of more elevated rear inflow, and a weaker convective updraft. The convective updraft is also slower to tilt rearward, and thus bowing occurs later. Graupel size distributions with more numerous, smaller, and lighter hydrometeors result in larger microphysical cooling rates, stronger cold pools, more intense midlevel buoyancy and pressure gradients, and earlier onset of surface-based rear inflow; these systems develop bowing segments earlier. A sensitivity test with fast-falling but small graupel hydrometeors revealed that small mean size and slow fall speed both contribute to the strong cooling rates. Simulations entirely without graupel are initially weaker, because of limited contributions from cooling by melting of the slowly falling snow. However, over the next hour increased rates of melting snow result in an increasingly more intense system with new bowing. Results of the study indicate that the development of a bow echo is highly sensitive to microphysical processes, which presents a challenge to the prediction of these severe weather phenomena.

Peering into the internal structure of cold pools and their interactions with a dense observational network

2021 ◽  
Author(s):  
Cathy Hohenegger ◽  
Jaemyeong Seo ◽  
Hannes Nevermann ◽  
Bastian Kirsch ◽  
Nima Shokri ◽  
...  
Keyword(s):  
Internal Structure ◽  
Land Surface ◽  
Surface Fluxes ◽  
Cold Pool ◽  
Convective Clouds ◽  
Cold Pools ◽  
Soil Sensors ◽  
Modelling Studies ◽  
Surface Network ◽  
Shed Light

<p>Melting and evaporation of hydrometeors in and below convective clouds generates cold, dense air that falls through the atmospheric column and spreads at the surface like a density current, the cold pool. In modelling studies, the importance of cold pools in controlling the lifecycle of convection has often been emphasized, being through their organization of the cloud field or through their sheer deepening of the convection. Larger, longer-lived cold pools benefit convection, but little is actually known on the size and internal structure of cold pools from observations as the majority of cold pools are too small to be captured by the operational surface network.  One aim of the field campaign FESSTVaL was to peer into the internal structure of cold pools and their interactions with the underlying land surface by deploying a dense network of surface observations. This network consisted of 80 self-designed cold pool loggers, 19 weather stations and 83 soil sensors deployed in an area of 15 km around Lindenberg. FESSTVaL took place from 17 May to 27 August 2021.</p> <p>In principle, cold pool characteristics are affected both by the atmospheric state, which fuels cold pools through melting and evaporation of hydrometeors, and the land surface, which acts to destroy cold pools through friction and warming by surface fluxes. In this talk, the measurements collected during FESSTVaL will be used to shed light on these interactions.  We are particularly interested to assess how homogeneous the internal structure of cold pools is and whether heterogeneities of the land surface imprint themselves on this internal structure. The results will be compared to available model simulations.</p>

A comparison study of aerosol impacts on idealized supercell between two bulk microphysics parameterizations

2020 ◽  
Author(s):  
Wanchen Wu ◽  
Wei Huang ◽  
Baode Chen
Keyword(s):  
Weather Prediction ◽  
Cloud Droplet ◽  
Forecast Model ◽  
Cloud Microphysics ◽  
Microphysics Scheme ◽  
Freezing Level ◽  
Cold Pools ◽  
Warm Rain ◽  
Warm Rain Process ◽  
Aerosol Effects

<p>Considering aerosol effects via microphysics parameterization is an imperative work in high-resolution numerical weather prediction. This paper uses two bulk microphysics parameterizations, Aerosol-Aware Thompson and CLR schemes, with the Weather and Research Forecast model to study the impacts of aerosols and microphysics scheme on an idealized supercell storm. Our results show that the implementation of aerosols can successfully modify the cloud droplet size and influence the subsequent warm-rain, mixed-phase, and accumulated precipitation. It implies that aerosols can make numerous differences to cloud microphysics properties and processes but the uncertainty in the magnitude of aerosol effects is huge because the two schemes are different from each other since the warm-rain process including CCN activation and rainwater formation. On the other hand, it is also found that the two schemes make tremendous differences in the rainfall pattern and storm dynamics due to the presence of graupel below the freezing level. The Thompson scheme has hail-like graupel which can fall below the freezing level to chill the air temperature effectively, intensify the downdraft, and enhance the uplifting on the front of cold pools. The mean graupel size represented by the two schemes plays a much more important role than the fall-speed formula for the dynamical feedbacks. Our results suggest that particle size is the core of a myriad of microphysics processes and highly associated with key cloud and dynamical signatures.</p>

Detection and Characterization of Cold Pools over Germany in the DYAMOND Simulations

2020 ◽  
Author(s):  
Jaemyeong Mango Seo ◽  
Cathy Hohenegger
Keyword(s):  
Wind Speed ◽  
General Circulation ◽  
Potential Temperature ◽  
Squall Line ◽  
Cold Pool ◽  
Characteristic Parameters ◽  
Pressure System ◽  
Low Area ◽  
Convective Clouds ◽  
Cold Pools

<p>Cold pool generated by convective clouds is an evaporatively cooled dry region which spreads out near the surface. Studying the cold pool characteristics enhances our understanding about convective clouds such as shallow-to-deep transition of convective clouds, long-lived squall line, and triggering secondary convection. In this study, cold pools over Germany are detected and characterized using phase 0 results of DYAMOND (stands for DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains) intercomparison project. We aim to understand how the cold pool characteristics over Germany depend on topographic height, accompanying cloud size, and model.</p><p>Nine model results of the DYAMOND collection are remapped into 0.1˚ × 0.1˚ regular grid system. Cold pool cluster is defined as a cluster with an area larger than ~64 km<sup>2</sup> (4 grids), with the perturbation virtual (density) potential temperature below 2 K and the maximum precipitation rate greater than 1 mm h<sup>–1</sup>. Detected cold pools are re-categorized by the topographic height to decompose cold pools related to orographic precipitation and by the accompanying cloud size to decompose cold pools related to large cloud system.</p><p>During simulated period (40 days from 1 August 2016), model averaged total detected cold pool number is 5.59 h<sup>–1</sup>. Although more number of cold pool clusters are detected over low topographic area (1.34 h<sup>–1</sup> and 4.25 h<sup>–1</sup> over high and low area, respectively), area weighted cold pool cluster number is 3.82 times larger over high topographic area (17.55 h<sup>–1</sup> and 4.60 h<sup>–1</sup> over high and low area, respectively). Most of cold pool clusters are accompanied by larger clouds than themselves (78 %) and 9 % of cold pools are detected outside of cloud cover. Except for the cold pools accompanied by clouds of synoptic low pressure system, most of cold pools are detected in the daytime. Cold pool clusters over high topographic area are larger, more non-circular shaped, colder, and with lower wind speed than those over low topographic area. Cold pool clusters accompanied by small clouds are colder, drier, with higher wind speed, and with stronger precipitation than those accompanied by large clouds. In this study, relationship between cold pool characteristic parameters in each category is also investigated. To understand how cold pool feature varies from model to model, the cold pool characteristic parameters in each DYAMOND model result are compared and analyzed.</p>

scholarly journals On Different Microphysical Pathways to Convective Rainfall

2018 ◽  
Vol 57 (10) ◽  
pp. 2399-2417 ◽  
Author(s):  
Sonia Lasher-Trapp ◽  
Shailendra Kumar ◽  
Daniel H. Moser ◽  
Alan M. Blyth ◽  
Jeffrey R. French ◽  
...  
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Cloud Droplet ◽  
Vertical Wind ◽  
Convective Precipitation ◽  
Convective Rainfall ◽  
Warm Rain ◽  
Warm Rain Process ◽  
Microphysical Processes ◽  
Ice Production

ABSTRACTThe Convective Precipitation Experiment (COPE) documented the dynamical and microphysical evolution of convection in southwestern England for testing and improving quantitative precipitation forecasting. A strong warm rain process was hypothesized to produce graupel quickly, initiating ice production by rime splintering earlier to increase graupel production and, ultimately, produce heavy rainfall. Here, convection observed on two subsequent days (2 and 3 August 2013) is used to test this hypothesis and illustrate how environmental factors may alter the microphysical progression. The vertical wind shear and cloud droplet number concentrations on 2 August were 2 times those observed on 3 August. Convection on both days produced comparable maximum radar-estimated rain rates, but in situ microphysical measurements indicated much less ice in the clouds on 2 August, despite having maximum cloud tops that were nearly 2 km higher than on 3 August. Idealized 3D numerical simulations of the convection in their respective environments suggest that the relative importance of particular microphysical processes differed. Higher (lower) cloud droplet number concentrations slow (accelerate) the warm rain process as expected, which in turn slows (accelerates) graupel formation. Rime splintering can explain the abundance of ice observed on 3 August, but it was hampered by strong vertical wind shear on 2 August. In the model, the additional ice produced by rime splintering was ineffective in enhancing surface rainfall; strong updrafts on both days lofted supercooled raindrops well above the 0°C level where they froze to become graupel. The results illustrate the complexity of dynamical–microphysical interactions in producing convective rainfall and highlight unresolved issues in understanding and modeling the competing microphysical processes.

scholarly journals The Formation of Wider and Deeper Clouds as a Result of Cold-Pool Dynamics

2014 ◽  
Vol 71 (8) ◽  
pp. 2842-2858 ◽  
Author(s):  
Linda Schlemmer ◽  
Cathy Hohenegger
Keyword(s):  
Deep Convection ◽  
Gravity Current ◽  
Cold Pool ◽  
Peak Time ◽  
Entrainment Rate ◽  
Convective Clouds ◽  
Cold Pools ◽  
Cloud Resolving Model ◽  
Cloud Development ◽  
Rain Formation

Abstract This study investigates how precipitation-driven cold pools aid the formation of wider clouds that are essential for a transition from shallow to deep convection. In connection with a temperature depression and a depletion of moisture inside developing cold pools, an accumulation of moisture in moist patches around the cold pools is observed. Convective clouds are formed on top of these moist patches. Larger moist patches form with time supporting more and larger clouds. Moreover, enhanced vertical lifting along the leading edges of the gravity current triggered by the cold pool is found. The interplay of moisture aggregation and lifting eventually promotes the formation of wider clouds that are less affected by entrainment and become deeper. These mechanisms are corroborated in a series of cloud-resolving model simulations representing different atmospheric environments. A positive feedback is observed in that, in an atmosphere in which cloud and rain formation is facilitated, stronger downdrafts will form. These stronger downdrafts lead to a stronger modification of the moisture field, which in turn favors further cloud development. This effect is not only observed in the transition phase but also active in prolonging the peak time of precipitation in the later stages of the diurnal cycle. These findings are used to propose a simple way for incorporating the effect of cold pools on cloud sizes and thereby entrainment rate into parameterization schemes for convection. Comparison of this parameterization to the cloud-resolving modeling output gives promising results.

scholarly journals Incorporation of inline warm-rain diagnostics into the COSP2 satellite simulator for process-oriented model evaluation

2019 ◽  
Author(s):  
Takuro Michibata ◽  
Kentaroh Suzuki ◽  
Tomoo Ogura ◽  
Xianwen Jing
Keyword(s):  
Regional Analysis ◽  
Model Performance ◽  
Multiple Model ◽  
Climatic Impact ◽  
Process Diagnostics ◽  
Post Process ◽  
Warm Rain ◽  
Process Oriented ◽  
Warm Rain Process ◽  
Microphysical Processes

Abstract. Cloud Feedback Model Intercomparison Project Observational Simulator Package (COSP) has been widely used to diagnose model performance and physical processes via an apple-to-apple comparison to satellite measurements. Although the COSP provides useful information about clouds and their climatic impact, outputs that have a subcolumn dimension require large amounts of data. This can cause a bottleneck when conducting sets of sensitivity experiments or multiple model intercomparisons. Here, we incorporate two diagnostics for warm-rain microphysical processes into COSP2, the latest version of the simulator. The approach used here employs existing diagnostic methodologies that probe how the warm-rain processes occur using statistics constructed from simulators of multiple satellite instruments along with their subcolumn information. The new diagnostics are designed to produce statistics online during the COSP execution, eliminating the need to output subcolumn variables. Users can also readily conduct regional analysis tailored to their particular research interest (e.g., land–ocean differences), using an auxiliary post-process package after the COSP calculation. This inline tool also generates global maps of the occurrence frequency of warm-rain regimes (i.e., non-precipitating, drizzling, and precipitating) classified according to CloudSat radar reflectivity, putting the warm-rain process diagnostics into the context of geographical distributions of precipitation. The inline diagnostics are applied to the MIROC6 GCM to demonstrate how known biases common among multiple GCMs relative to satellite observations are revealed. The inline multisensor diagnostics are intended to serve as a tool that facilitates process-oriented model evaluations in a manner that reduces the burden on modelers for their diagnostics effort.

scholarly journals Surface Cold Pools in the Outer Rainbands of Tropical Storm Hanna (2008) Near Landfall

2012 ◽  
Vol 140 (2) ◽  
pp. 471-491 ◽  
Author(s):  
Matthew D. Eastin ◽  
Tiffany L. Gardner ◽  
M. Christopher Link ◽  
Kelly C. Smith
Keyword(s):  
Potential Temperature ◽  
Leading Edge ◽  
Tropical Storm ◽  
Vertical Shear ◽  
Cold Pool ◽  
Cold Pools ◽  
Pressure Anomaly ◽  
Cyclonic Flow ◽  
Convective Cells ◽  
Pool Formation

Surface mesonet observations were used to document the structure of prominent cold pools associated with two convective outer rainbands of Tropical Storm Hanna on 5 September 2008. The developing rainbands were located ~400 km north of the storm center as they crossed the Carolina coastline and passed over the mesonet. The combination of moderate CAPE, moderate low-level cross-band vertical shear, and dry midlevel air provided an environment supportive of surface cold pool formation and long-lived quasi-linear convection. Both rainbands exhibited multiple outward-tilting convective cells and discrete line segments centered within a narrow zone of nearly continuous stratiform precipitation. The mesonet observations provided a unique along- and cross-band perspective of discrete cold pools situated beneath and behind the convection portions of each rainband. Prominent cold pools extended 40–80 km behind the rainband’s leading edge and exhibited maximum potential temperature, mixing ratio, and equivalent potential temperature deficits of 2–4 K, 1–2 g kg−1, and 4–10 K, respectively. In the cross-band direction, convergence of storm-relative inflow along the cold pool leading edge was coincident with a modest high pressure anomaly, while inflow divergence prevailed through the cold pool and rainfall maxima. Several cold pools expanded along-band while being advected downband by the prevailing cyclonic flow. Cold pool wakes were observed more than 50 km behind the rainband leading edge and up to 20 km downband from intense convection. Variations in cold pool intensity were not well correlated with convective intensity, rainfall rate, or the degree of midlevel dryness. Implications of prominent cold pools on tropical cyclone convection, size, and intensity are discussed.

scholarly journals Machine Learning the Warm Rain Process

2020 ◽  
Author(s):  
Andrew Gettelman ◽  
David John Gagne ◽  
Chih-Chieh Chen ◽  
Matthew Christensen ◽  
Zachary Lebo ◽  
...  
Keyword(s):  
Machine Learning ◽  
Warm Rain ◽  
Warm Rain Process

Cold Pools and Their Influence on the Tropical Marine Boundary Layer

2017 ◽  
Vol 74 (4) ◽  
pp. 1149-1168 ◽  
Author(s):  
Simon P. de Szoeke ◽  
Eric D. Skyllingstad ◽  
Paquita Zuidema ◽  
Arunchandra S. Chandra
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Sensible Heat Flux ◽  
Surface Flux ◽  
Active Phase ◽  
Surface Fluxes ◽  
Cold Pool ◽  
Madden Julian Oscillation ◽  
Cold Pools ◽  
Central Indian Ocean

Abstract Cold pools dominate the surface temperature variability observed over the central Indian Ocean (0°, 80°E) for 2 months of research cruise observations in the Dynamics of the Madden–Julian Oscillation (DYNAMO) experiment in October–December 2011. Cold pool fronts are identified by a rapid drop of temperature. Air in cold pools is slightly drier than the boundary layer (BL). Consistent with previous studies, cold pools attain wet-bulb potential temperatures representative of saturated downdrafts originating from the lower midtroposphere. Wind and surface fluxes increase, and rain is most likely within the ~20-min cold pool front. Greatest integrated water vapor and liquid follow the front. Temperature and velocity fluctuations shorter than 6 min achieve 90% of the surface latent and sensible heat flux in cold pools. The temperature of the cold pools recovers in about 20 min, chiefly by mixing at the top of the shallow cold wake layer, rather than by surface flux. Analysis of conserved variables shows mean BL air is composed of 51% air entrained from the BL top (800 m), 22% saturated downdrafts, and 27% air at equilibrium with the ocean surface. The number of cold pools, and their contribution to the BL heat and moisture, nearly doubles in the convectively active phase compared to the suppressed phase of the Madden–Julian oscillation.

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