scholarly journals A New Parameterization of the Accretion of Cloud Water by Graupel and Its Evaluation through Cloud and Precipitation Simulations

2019 ◽  
Vol 76 (2) ◽  
pp. 381-400 ◽  
Author(s):  
Han-Gyul Jin ◽  
Hyunho Lee ◽  
Jong-Jin Baik
Keyword(s):  
Collection Efficiency ◽  
Precipitation Amount ◽  
Cloud Droplet ◽  
Convective Cloud ◽  
Heavy Precipitation ◽  
Cloud Water ◽  
The Other ◽  
Precipitation Event ◽  
Cloud Droplets ◽  
Cloud Resolving Model

Abstract A new parameterization of the accretion of cloud water by graupel for use in bulk microphysics schemes is derived by analytically integrating the stochastic collection equation (SCE). In this parameterization, the collection efficiency between graupel particles and cloud droplets is expressed in a functional form using the data obtained from a particle trajectory model by a previous study. The new accretion parameterization is evaluated through box model simulations in comparison with a bin-based direct SCE solver and two previously developed accretion parameterizations that employ the continuous collection equation and a simplified SCE, respectively. Changes in cloud water and graupel mass contents via the accretion process predicted by the new parameterization are closest to those predicted by the direct SCE solver. Furthermore, the new parameterization predicts a decrease in the cloud droplet number concentration that is smaller than the decreases predicted by the other accretion parameterizations, consistent with the direct SCE solver. The new and the other accretion parameterizations are implemented into a cloud-resolving model. Idealized deep convective cloud simulations show that among the accretion parameterizations, the new parameterization predicts the largest rate of accretion by graupel and the smallest rate of accretion by snow, which overall enhances rainfall through the largest rate of melting of graupel. Real-case simulations for a precipitation event over the southern Korean Peninsula show that among the examined accretion parameterizations, the new parameterization simulates precipitation closest to observations. Compared to the other accretion parameterizations, the new parameterization decreases the fractions of light and moderate precipitation amounts and increases the fraction of heavy precipitation amount.

A new parameterization of the accretion of cloud water by snow and its evaluation through simulations of mesoscale convective systems

2020 ◽  
Author(s):  
Han-Gyul Jin ◽  
Jong-Jin Baik
Keyword(s):  
Mesoscale Convective System ◽  
Cloud Droplet ◽  
Spherical Shape ◽  
Heavy Precipitation ◽  
Cloud Water ◽  
Squall Line ◽  
Convective System ◽  
Cloud Droplets ◽  
Convective Systems ◽  
Mesoscale Convective

<p>A new parameterization of the accretion of cloud water by snow for use in bulk microphysics schemes is derived by analytically solving the stochastic collection equation (SCE), where the theoretical collision efficiency for individual snowflake–cloud droplet pairs is applied. The snowflake shape is assumed to be nonspherical with the mass- and area-size relations suggested by an observational study. The performance of the new parameterization is compared to two parameterizations based on the continuous collection equation, one with the spherical shape assumption for snowflakes (SPH-CON), and the other with the nonspherical shape assumption employed in the new parameterization (NSP-CON). In box model simulations, only the new parameterization reproduces a relatively slow decrease in the cloud droplet number concentration which is predicted by the direct SCE solver. This results from considering the preferential collection of cloud droplets depending on their sizes in the new parameterization based on the SCE. In idealized squall-line simulations using a cloud-resolving model, the new parameterization predicts heavier precipitation in the convective core region compared to SPH-CON, and a broader area of the trailing stratiform rain compared to NSP-CON due to the horizontal advection of greater amount of snow in the upper layer. In the real-case simulations of a line-shaped mesoscale convective system that passed over the central Korean Peninsula, the new parameterization predicts higher frequencies of light precipitation rates and lower frequencies of heavy precipitation rates. The relatively large amount of upper-level snow in the new parameterization contributes to a broadening of the area with significant snow water path.</p>

A New Parameterization of the Accretion of Cloud Water by Snow and Its Evaluation through Simulations of Mesoscale Convective Systems

2020 ◽  
Vol 77 (8) ◽  
pp. 2885-2903
Author(s):  
Han-Gyul Jin ◽  
Jong-Jin Baik
Keyword(s):  
Mesoscale Convective System ◽  
Cloud Droplet ◽  
Spherical Shape ◽  
Heavy Precipitation ◽  
Cloud Water ◽  
Squall Line ◽  
Convective System ◽  
Analytic Approximation ◽  
Cloud Droplets ◽  
Mesoscale Convective

Abstract A new parameterization of the accretion of cloud water by snow for use in bulk microphysics schemes is derived as an analytic approximation of the stochastic collection equation (SCE), where the theoretical collision efficiency for individual snowflake–cloud droplet pairs is applied. The snowflake shape is assumed to be nonspherical with the mass–size and area–size relations suggested by an observational study. The performance of the new parameterization is compared to two parameterizations based on the continuous collection equation, one with the spherical shape assumption for snowflakes (SPH-CON), and the other with the nonspherical shape assumption employed in the new parameterization (NSP-CON). In box model simulations, only the new parameterization reproduces a relatively slow decrease in the cloud droplet number concentration, which is predicted by the direct SCE solver. This results from considering the preferential collection of cloud droplets depending on their sizes in the new parameterization based on the SCE. In idealized squall-line simulations using a cloud-resolving model, the new parameterization predicts heavier precipitation in the convective core region compared to SPH-CON, and a broader area of the trailing stratiform rain compared to NSP-CON due to the horizontal advection of greater amount of snow in the upper layer. In the real-case simulations of a line-shaped mesoscale convective system that passed over the central Korean Peninsula, the new parameterization predicts higher frequencies of light precipitation rates and lower frequencies of heavy precipitation rates. The relatively large amount of upper-level snow in the new parameterization contributes to a broadening of the area with significant snow water path.

scholarly journals Spatial relationship between the atmospheric circulation and the precipitation measured in the western Swiss Alps by means of the analogue method

2012 ◽  
Vol 12 (3) ◽  
pp. 777-784 ◽  
Author(s):  
P. Horton ◽  
M. Jaboyedoff ◽  
R. Metzger ◽  
C. Obled ◽  
R. Marty
Keyword(s):  
Atmospheric Circulation ◽  
Precipitation Amount ◽  
Heavy Precipitation ◽  
Swiss Alps ◽  
Precipitation Event ◽  
Circulation Patterns ◽  
Analogue Method ◽  
Western Swiss Alps ◽  
Time Extrapolation ◽  
Precipitation Events

Abstract. An adaptation technique based on the synoptic atmospheric circulation to forecast local precipitation, namely the analogue method, has been implemented for the western Swiss Alps. During the calibration procedure, relevance maps were established for the geopotential height data. These maps highlight the locations were the synoptic circulation was found of interest for the precipitation forecasting at two rain gauge stations (Binn and Les Marécottes) that are located both in the alpine Rhône catchment, at a distance of about 100 km from each other. These two stations are sensitive to different atmospheric circulations. We have observed that the most relevant data for the analogue method can be found where specific atmospheric circulation patterns appear concomitantly with heavy precipitation events. Those skilled regions are coherent with the atmospheric flows illustrated, for example, by means of the back trajectories of air masses. Indeed, the circulation recurrently diverges from the climatology during days with strong precipitation on the southern part of the alpine Rhône catchment. We have found that for over 152 days with precipitation amount above 50 mm at the Binn station, only 3 did not show a trajectory of a southerly flow, meaning that such a circulation was present for 98% of the events. Time evolution of the relevance maps confirms that the atmospheric circulation variables have significantly better forecasting skills close to the precipitation period, and that it seems pointless for the analogue method to consider circulation information days before a precipitation event as a primary predictor. Even though the occurrence of some critical circulation patterns leading to heavy precipitation events can be detected by precursors at remote locations and 1 week ahead (Grazzini, 2007; Martius et al., 2008), time extrapolation by the analogue method seems to be rather poor. This would suggest, in accordance with previous studies (Obled et al., 2002; Bontron and Obled, 2005), that time extrapolation should be done by the Global Circulation Model, which can process atmospheric variables that can be used by the adaptation method.

Numerical Simulations of Convective Cloud Merging Processes at Different Development Stages

2020 ◽  
Author(s):  
Jing Zhai ◽  
Yong Huang
Keyword(s):  
Mesoscale Model ◽  
Convective Cloud ◽  
Cloud Water ◽  
The Other ◽  
Small Cells ◽  
Horizontal Scale ◽  
Development Stages ◽  
Ice Surface ◽  
Radar Echo ◽  
Simulation Results

<p>Mergers of cells in a severe convective weather on 22 July 2008 are simulated and analyzed by Mesoscale Model 5 (referred to as MM5）and radar network data. Observation results show that, the horizontal scale of the echo above 30 dBZ, which represent the small cells, is about 10 km, and the small cells that the echo centers are 20km apart merge into a larger cell at dozens of km of horizontal scale.. Mergers begin from the peripheral radar echo, and then strong central radar echo merges at the low level, at last, the acreage of strong radar echo increases after the merger. The contrast between the observations and the simulation results shows that they are consistent. Analysis on the simulation results of two kinds of cell mergers at different development stages based on the third network model output shows that, while the cell pairs are with almost the same intensity, cells would develop after merger; while one of the cell pairs is in stronger development however the other one weaker, the stronger cell would keep on development and the weaker cell would die out. During the merger, a new cloud water center appears in the low convergence region between the cell pairs, and would replace the two cloud water centers of the former cells, or the new cloud water center would merger with one of the old cloud water centers while the other old cloud water center disappears. The analysis of the simulation results also shows that, the cell merger would lead to the cloud top lifting and the increase in the radar echo, content of cloud water and ice, surface rainfall.</p>

scholarly journals Strong sensitivity of aerosol concentrations to convective wet scavenging parameterizations in a global model

2012 ◽  
Vol 12 (1) ◽  
pp. 1687-1732 ◽  
Author(s):  
B. Croft ◽  
J. R. Pierce ◽  
R. V. Martin ◽  
C. Hoose ◽  
U. Lohmann
Keyword(s):  
Cloud Droplet ◽  
Convective Cloud ◽  
Cloud Base ◽  
Ice Crystal ◽  
Cloud Droplets ◽  
Convective Clouds ◽  
The Standard Model ◽  
Wet Scavenging ◽  
Limiting Case ◽  
Precipitation Formation

Abstract. This study examines the influences of assumptions in convective wet scavenging parameterizations on global climate model simulations of aerosol concentrations and wet deposition. To facilitate this study, an explicit representation of the uptake of aerosol mass and number into convective cloud droplets and ice crystals by the processes of activation, collisions, freezing and evaporation is introduced into the ECHAM5-HAM model. This development replaces the prescribed aerosol cloud-droplet-borne/ice-crystal-borne fractions of the standard model. Relative to the standard model, the more consistent treatment between convective aerosol-cloud microphysical processes yields a reduction of aerosol wet removal in mixed liquid and ice phase convective clouds by at least a factor of two, and the global, annual mean aerosol burdens are increased by at least 20%. Two limiting cases regarding the wet scavenging of entrained aerosols are considered. In the first case, aerosols entering convective clouds at their bases are the only aerosols that are scavenged into cloud droplets, and are susceptible to removal by convective precipitation formation. In the second case, aerosols that are entrained into the cloud above the cloud base layer can activate, can collide with existing cloud droplets and ice crystals, and can subsequently be removed by precipitation formation. The limiting case that allows aerosols entrained above cloud base to become cloud-droplet-borne and ice-crystal-borne reduces the annual and global mean aerosol burdens by 30% relative to the other limiting case, and yields the closest agreement with global aerosol optical depth retrievals, and black carbon vertical profiles from aircraft campaigns (changes of about one order of magntiude in the upper troposphere). Predicted convective cloud droplet number concentrations are doubled in the tropical middle troposphere when aerosols entrained above cloud base are allowed to activate. These results show that aerosol concentrations and wet deposition predicted in a global model are strongly sensitive to the assumptions made regarding the wet scavenging of aerosols in convective clouds.

scholarly journals Impacts of solar-absorbing aerosol layers on the transition of stratocumulus to trade cumulus clouds

2017 ◽  
Author(s):  
Xiaoli Zhou ◽  
Andrew S. Ackerman ◽  
Ann M. Fridlind ◽  
Robert Wood ◽  
Pavlos Kollias
Keyword(s):  
Radiative Forcing ◽  
Cloud Droplet ◽  
Cloud Water ◽  
Gradual Transition ◽  
Liquid Water Path ◽  
Diffusional Growth ◽  
Cumulus Clouds ◽  
Cloud Droplets ◽  
Boundary Layer Height ◽  
Cloud Droplet Number Concentration

Abstract. The effects of an initially overlying layer of solar-absorbing aerosol on the transition of stratocumulus to trade cumulus clouds are examined using large-eddy simulations. The transition of lightly drizzling cloud is generally hastened, resulting mainly from increased cloud droplet number concentration (Nc) induced by entrained aerosol. The increased Nc slows sedimentation of cloud droplets and shortens their relaxation time for diffusional growth, both of which accelerate entrainment of overlying air and thereby stratocumulus breakup. However, the decrease in albedo from cloud breakup is more than offset by redistributing cloud water over a greater number of droplets, such that the diurnal-average shortwave forcing at the top of atmosphere is negative. The negative radiative forcing is enhanced by sizable longwave contributions, which result from the greater cloud breakup and a reduced boundary layer height associated with aerosol heating. A perturbation of moisture instead of aerosol aloft leads to greater liquid water path and a more gradual transition. Adding absorbing aerosol to that atmosphere results in substantial reductions in LWP and cloud cover that lead to positive shortwave and negative longwave forcings on average canceling each other. Only for heavily drizzling clouds is the breakup delayed, as inhibition of precipitation overcomes cloud water loss from enhanced entrainment. Considering these simulations as an imperfect proxy for biomass burning plumes influencing Namibian stratocumulus, we expect regional indirect plus semi-direct forcings to be substantially negative to negligible at the top of atmosphere, with its magnitude sensitive to background and perturbation properties.

Assessment of Urbanization Impact On Heavy Precipitation in Istanbul, Turkey

2021 ◽  
Author(s):  
Kutay Dönmez ◽  
Berkay Dönmez ◽  
Deniz Diren-Üstün ◽  
Yurdanur Ünal
Keyword(s):  
Land Use ◽  
Precipitation Amount ◽  
Heavy Precipitation ◽  
Heat Fluxes ◽  
Precipitation Event ◽  
Total Precipitation ◽  
Land Use Type ◽  
Start Time ◽  
Heavy Precipitation Event ◽  
The Impact

<p>Cities have undergone a substantial increase in urbanization over the past decades. Whether the change in land-use type and the consequent Urban Heat Island (UHI) affects the extreme precipitation was of interest and has been under investigation for various developing cities. This study pursued a similar purpose and investigated the impact of urbanization on a heavy precipitation incident that took place in Istanbul on 18 July 2017. Two particular land-use scenarios were used to simulate the event by Weather Research and Forecasting Model (WRF). First, the control simulation (WRF-urban) was performed using the default CORINE 2018 land-use dataset. Subsequently, the test simulation (WRF-nourban) was implemented by replacing the urbanized land-use type of Istanbul with the most dominant land use category of arid cultivated area. Comparison of the WRF-urban simulation with station observations and satellite data reveal that the WRF captured the heavy precipitation event reasonably well over Istanbul.  Results showed that urbanization has a notable impact on both the magnitude and timing of heavy rainfall.  Event day total precipitation amount increased considerably over and downstream of Istanbul on the control run. Although the start time and location of the incident reasonably matched for both runs, the test run without urbanization advanced the rainfall quicker, and the heavy precipitation event took place 1 hour earlier than the control run. The most pronounced distinction between the simulations with and without urbanization is detected over the northern coasts of Istanbul as the maximum daily total precipitation amount was approximately 250 mm higher just upstream and downstream of Istanbul Airport (IGA) on the WRF-urban run. Analysis of both vertical cross-sections and sensible heat fluxes on the city revealed that urbanized areas increased the atmospheric instability, thus caused heavier precipitation.</p>

scholarly journals Experimental Study of Collection Efficiencies between Submicron Aerosols and Cloud Droplets

2011 ◽  
Vol 68 (9) ◽  
pp. 1853-1864 ◽  
Author(s):  
Luis Ladino ◽  
Olaf Stetzer ◽  
Bodo Hattendorf ◽  
Detlef Günther ◽  
Betty Croft ◽  
...  
Keyword(s):  
Inductively Coupled Plasma ◽  
Collection Efficiency ◽  
Pure Water ◽  
Cloud Droplet ◽  
Cloud Droplets ◽  
Inductively Coupled ◽  
Aerosol Mass ◽  
Order Of Magnitude ◽  
Plasma Mass Spectrometry ◽  
Experimental Values

Abstract Collection efficiency E experiments for aerosol particles scavenged by cloud droplets were carried out in the newly built Collision Ice Nucleation Chamber (CLINCH). Pure water droplets having radii between 12.8 and 20.0 μm were allowed to fall freely and to collide in a laminar flow with lithium metaborate particles having radii between 0.05 and 0.33 μm. At the bottom of the chamber, the droplets and the particles captured were collected using a cup impactor. The collected solution was analyzed for the scavenged aerosol mass by inductively coupled plasma mass spectrometry. Evaporation of droplets was taken into account since the relative humidity inside the chamber was below 100%, resulting in final theoretical droplet sizes between 4.2 and 17.6 μm. The resulting experimental measurements were compared with theoretical values to see their correlation. The authors found an experimental trend similar to theory, as well as the “Greenfield gap” at the particle radius of 0.24 μm (E = 0.038) for the smallest cloud droplet size investigated in this study. The experimental values of collection efficiency found herein agree with those from theory within one order of magnitude, similar to previous studies reported in the literature.

scholarly journals Improving the detailing of atmospheric processes modelling using the Polar WRF model: a case study of a heavy rainfall event at the Akademik Vernadsky station

2020 ◽  
pp. 26-41
Author(s):  
D. Pishniak ◽  
◽  
B. Beznoshchenko ◽  
Keyword(s):  
Surface Temperature ◽  
Antarctic Peninsula ◽  
Precipitation Amount ◽  
Heavy Precipitation ◽  
Horizontal Resolution ◽  
Precipitation Event ◽  
Heavy Rainfall Event ◽  
In Situ Observation ◽  
Near Surface ◽  
The Antarctic

The Antarctic Peninsula region is of growing interest due to the regional climate change features and related atmospheric circulation patterns. The regional mesoscale atmospheric model Polar Weather Research and Forecasting (WRF) v4.1.1 was used in this research to study a heavy precipitation event over the Ukrainian Antarctic Akademik Vernadsky station region (Antarctic Peninsula). The passage of the cyclone over the Antarctic Peninsula as a typical synoptic process as well as a case of the daily precipitation maximum amount of 2018 were chosen for investigation in this research. The estimation of the modelling quality and downscaling was done by comparing the obtained results with in-situ observation at the Akademik Vernadsky station and cross-domain tracking of average meteorological values and their deviation. The concept of the nested domains allowed to increase the horizontal resolution of the simulated atmosphere up to 1 km and to reproduce the wind regime of this region with high quality. Comparison with measured data showed a significant improvement in wind simulation with increasing of resolution, but worse representation of surface temperature and humidity. The Polar WRF made a general cooling of near surface temperature of 2 °C during the period of simulation and increased precipitation amount by 4.6–8.4 mm (12–21%) on average over the territory relative to the initial data from Global Data Assimilation System. This can be explained by the contribution of noise and imperfection of the model (including static input data of the terrain description). Based on the modelled results, the interaction of wind flow with the mountainous terrain of the Antarctic Peninsula creates a range of complex dynamic effects in the atmosphere. These effects cause local precipitation maxima both over the Peninsula and over the adjacent ocean. These are, respectively, bay-valley areas of increased precipitation and increased precipitation on the crests of shock waves from orographic obstacles. Under certain background wind conditions, the influence of the latter effect can reach the Akademik Vernadsky station and cause the formation of heavy precipitation here.

scholarly journals The Role of Aerosols in Convective Processes during the Midsummer Drought in the Caribbean

2015 ◽  
Vol 2015 ◽  
pp. 1-16 ◽  
Author(s):  
Nathan Hosannah ◽  
Hamed Parsiani ◽  
Jorge E. González
Keyword(s):  
Heavy Precipitation ◽  
Atmospheric Modeling ◽  
Dew Point ◽  
Saharan Dust ◽  
Convective Precipitation ◽  
Precipitation Event ◽  
Atmospheric Conditions ◽  
Cloud Resolving Model ◽  
The Caribbean

Saharan dust (SD) heavily impacts convective precipitation in the Caribbean. To better understand the role of SD in precipitation development during the midsummer drought (MSD), an observational campaign, centered at the city of Mayagüez, Puerto Rico (18.21 N, 67.13 W), between 3 June and 15 July 2014, was conducted in order to select a range of atmospheric conditions to be simulated using the Regional Atmospheric Modeling System (RAMS) cloud resolving model under “no SD” and “SD” conditions. The events included one dry day with moderate-heavy SD, one localized moderate rainfall event with moderate SD, one island-wide light precipitation event with heavy SD, and one island-wide heavy precipitation event with light-moderate SD. Model results show that (1) precipitation results are improved when compared with observation with the presence of SD, (2) precipitation, cloud fraction, dew point temperatures, and humidity are significantly reduced under SD conditions, (3) precipitation can occur when SD is removed for a dry day, (4) there is evidence of rain being delayed due to the presence of SD without rainfall intensity or accumulation increases, (5) liquid mixing ratio increases of up to 1.4 g kg−1occur in the absence of SD, and (6) vertical wind increases of up to 0.8 m s−1occur in the absence of SD.

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