scholarly journals Microphysics impacts on the warm conveyor belt and ridge building of the NAWDEX IOP6 cyclone

2021 ◽  
Author(s):  
Marie Mazoyer ◽  
Didier Ricard ◽  
Gwendal Rivière ◽  
Julien Delanoë ◽  
Philippe Arbogast ◽  
...  
Keyword(s):  
Conveyor Belt ◽  
Heating Rates ◽  
Melting Layer ◽  
The North ◽  
Ice Water Content ◽  
Diabatic Processes ◽  
Upper Level ◽  
The One ◽  
Mixed Phase Clouds ◽  
Ice Water

AbstractThis study investigates diabatic processes along the warm conveyor belt (WCB) of a deep extra-tropical cyclone observed of the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX). The aim is to investigate the effect of two different microphysics schemes, the one-moment scheme ICE3 and the quasi two-moment scheme LIMA, on the WCB and the ridge building downstream. ICE3 and LIMA also differ on the processes of vapor deposition on hydrometeors in cold and mixed-phase clouds. Latent heating in ICE3 is found to be dominated by deposition on ice while the heating in LIMA is distributed among depositions on ice, snow and graupel. ICE3 is the scheme leading to the largest number of WCB trajectories (30% more than LIMA) due to greater heating rates over larger areas. The consequence is that the size of the upper-level ridge is growing more rapidly in ICE3 than LIMA, albeit with some exceptions in localized regions of the cyclonic branch of the WCB. A comparison with various observations (airborne remote sensing measurements, dropsondes and satellite data) is then performed. Below the melting layer, the observed reflectivity is rather well reproduced by the model. Above the melting layer, in the middle of the troposphere, the reflectivity and retrieved ice water content are largely underestimated by both schemes while at upper levels, the ICE3 scheme performs much better than LIMA in agreement with a closer representation of the observed winds by ICE3. These results underline the strong sensitivity of upper-level dynamics to ice related processes.

scholarly journals On the Co-Occurrence of Warm Conveyor Belt Outflows and PV Streamers*

2014 ◽  
Vol 71 (10) ◽  
pp. 3668-3673 ◽  
Author(s):  
Erica Madonna ◽  
Sebastian Limbach ◽  
Christine Aebi ◽  
Hanna Joos ◽  
Heini Wernli ◽  
...  
Keyword(s):  
Life Cycle ◽  
Three Dimensional ◽  
Conveyor Belt ◽  
Rossby Wave Breaking ◽  
Weather Forecasts ◽  
Three Dimensional Objects ◽  
The North ◽  
Conveyor Belts ◽  
Diabatic Processes ◽  
Warm Conveyor Belts

Abstract The co-occurrence of warm conveyor belts (WCBs), strongly ascending moist airstreams in extratropical cyclones, and stratospheric potential vorticity (PV) streamers, indicators for breaking Rossby waves on the tropopause, is investigated for a 21-yr period in the Northern Hemisphere using Interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) data. WCB outflows and PV streamers are respectively identified as two- and three-dimensional objects and tracked during their life cycle. PV streamers are more frequent than WCB outflows and nearly 15% of all PV streamers co-occur with WCBs during their life cycle, whereas about 60% of all WCB outflows co-occur with PV streamers. Co-occurrences are most frequent over the North Atlantic and North Pacific in spring and winter. WCB outflows are often located upstream of the PV streamers and form earlier, indicating the importance of diabatic processes for downstream Rossby wave breaking. Less frequently, PV streamers occur first, leading to the formation of new WCBs.

Retrieval and Evaluation of Ice Water Content from the Airborne Wyoming Cloud Radar in Orographic Wintertime Clouds during SNOWNIE

2021 ◽  
Keyword(s):  
Water Content ◽  
Sensitivity Study ◽  
Mixed Phase ◽  
Zero Bias ◽  
Cloud Radar ◽  
Ice Water Content ◽  
The University ◽  
Mixed Phase Clouds ◽  
Ice Water

Abstract The ice water content (IWC) in ice and mixed-phase clouds is retrieved from airborne Wyoming Cloud Radar (WCR) measurements aboard the University of Wyoming King Air (UWKA), which has a suite of integrated in situ IWC, optical array probes (OAP) and remote sensing measurements and provides a unique dataset for this algorithm development and evaluation. A sensitivity study with different idealized ice particle habits shows that the retrieved IWC with aggregate ice particle habit agrees the best with the in situ measurement, especially in ice or ice-dominated mixed-phase clouds with a correlation coefficient (rr) of 0.91 and close-to-zero bias. For mixed-phase clouds with ice fraction ratio less than 0.8, the variances of IWC estimates increase (rr = 0.76) and the retrieved mean IWC is larger than in situ IWC by a factor of 2. This is found to be related to the uncertainty of in situ measurements, the large cloud inhomogeneity, and the retrieval assumption uncertainty. The simulated reflectivity (Ze) and IWC relationships assuming three idealized ice particle habits and measured particle size distributions show that hexagonal columns with the same Ze have a lower IWC than aggregates, whose Ze-IWC relation is more consistent with the observed WCR Ze and in-situ IWC relation in those clouds. The 2DS images also indicate that ice particle habit transition occurs in orographic mixed-phase clouds, hence the retrieved IWC assuming modified Gamma PSD of aggregate particles tends to be biased larger in this kind of clouds.

scholarly journals Organization of convective ascents in a warm conveyor belt

2020 ◽  
Author(s):  
Nicolas Blanchard ◽  
Florian Pantillon ◽  
Jean-Pierre Chaboureau ◽  
Julien Delanoë
Keyword(s):  
Large Scale ◽  
Doppler Radar ◽  
Heavy Precipitation ◽  
Conveyor Belt ◽  
Isolated Cells ◽  
Low Level ◽  
The North ◽  
Low Level Jet ◽  
Upper Level ◽  
The Impact

Abstract. Warm conveyor belts (WCBs) are warm, moist airstreams of extratropical cyclones leading to widespread clouds and heavy precipitation, where associated diabatic processes can influence midlatitude dynamics. Although WCBs are traditionally seen as continuous slantwise ascents, recent studies have emphasized the presence of embedded convection and the production of mesoscale bands of negative potential vorticity (PV), the impact of which on large-scale dynamics is still debated. Here, detailed cloud and wind measurements obtained with airborne Doppler radar provide unique information on the WCB of the Stalactite cyclone on 2 October 2016 during the North Atlantic Waveguide and Downstream Impact Experiment. The measurements are complemented by a convection-permitting simulation, enabling online Lagrangian trajectories and 3-D objects clustering. The simulation reproduces well the mesoscale structure of the cyclone shown by satellite infrared observations, while the location of trajectories rising by 150 hPa during a relatively short 12 h window matches the WCB region expected from high clouds. One third of those trajectories, categorized as fast ascents, further reach a 100 hPa (2h)−1 threshold during their ascent and follow the cyclonic flow mainly at lower levels. In agreement with radar observations, convective updrafts are found in the WCB and are characterized by moderate reflectivity values up to 20 dBz and vertical velocities above 0.3 m s−1. Updraft objects and fast ascents consistently show three main types of convection in the WCB: (i) frontal convection along the surface cold front and the western edge of the low-level jet; (ii) banded convection at about 2 km altitude along the eastern edge of the low-level jet; (iii) mid-level convection below the upper-level jet. Mesoscale PV dipoles with strong positive and negative values are located in the vicinity of convective ascents and appear to accelerate both low-level and upper-level jets. Both convective ascents and negative PV organize into structures with coherent shape, location and evolution, thus suggesting a dynamical linkage. The results show that convection embedded in WCBs occurs in a coherent and organized manner rather than as isolated cells.

scholarly journals Mid-level convection in a warm conveyor belt accelerates the jet stream

2020 ◽  
Author(s):  
Nicolas Blanchard ◽  
Florian Pantillon ◽  
Jean-Pierre Chaboureau ◽  
Julien Delanoë
Keyword(s):  
Large Scale ◽  
Doppler Radar ◽  
Conveyor Belt ◽  
Jet Stream ◽  
Lagrangian Analysis ◽  
Sensitivity Experiment ◽  
The North ◽  
Mesoscale Structures ◽  
Upper Level ◽  
The Impact

Abstract. Jet streams and potential vorticity (PV) gradients along upper-level ridges and troughs form a waveguide that governs midlatitude dynamics. Warm conveyor belt (WCB) outflows often inject low-PV air into ridges and their representation is seen as a source of uncertainty for downstream forecasts. Recent studies have highlighted the presence of mesoscale structures of negative PV in WCBs, the impact of which on large-scale dynamics is still debated. Here, fine-scale observations of cloud and wind structures acquired with airborne Doppler radar and dropsondes provide rare information on the WCB outflow of the Stalactite cyclone and the associated upper-level ridge on 2 October 2016 during the North Atlantic Waveguide and Downstream Impact Experiment. The observations reveal a complex tropopause structure with a high PV tongue separating the northwestern edge of the ridge in two parts, each with cirrus-type clouds and accompanied by a jet stream core, and bounded by a tropopause fold. A reference, convection-permitting simulation with full physics reproduces well the observed mesoscale structures and reveals the presence of elongated negative PV bands along the eastern jet stream core. In contrast, a sensitivity experiment with heat exchanges due to cloud processes cut off shows lower cloud tops, weaker jet stream cores, a ridge less extended westward, and the absence of negative PV bands. A Lagrangian analysis based on online trajectories shows that the anticyclonic branch of the WCB outflow feeds the eastern jet stream core in the reference simulation, while it is absent in the sensitivity experiment. The anticyclonic ascents and negative PV bands originate from the same region near the cyclone's bent-back front. The most rapid ascents coincide with mid-level convective cells identified by clustering analysis, which are located in a region of conditional instability below the jet stream core and above a low-level jet. Horizontal PV dipoles are found around these cells and with the negative poles reaching absolute negative values, thus appear as the source of negative PV bands. The results show that mid-level convection within WCBs accelerates the jet stream and may thus influence the downstream large-scale circulation.

scholarly journals Properties of Arctic liquid and mixed phase clouds from ship-borne Cloudnet observations during ACSE 2014

2020 ◽  
Author(s):  
Peggy Achtert ◽  
Ewan J. O'Connor ◽  
Ian M. Brooks ◽  
Georgia Sotiropoulou ◽  
Matthew D. Shupe ◽  
...  
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Liquid Water Content ◽  
Mixed Phase ◽  
Cloud Base ◽  
Ice Clouds ◽  
Ice Water Content ◽  
Mixed Phase Clouds ◽  
Ice Water ◽  
Cloud Top Temperature

Abstract. This study presents Cloudnet retrievals of Arctic clouds from measurements conducted during a three-month research expedition along the Siberian shelf during summer and autumn 2014. During autumn, we find a strong reduction in the occurrence of liquid clouds and an increase for both mixed-phase and ice clouds at low levels compared to summer. About 80 % of all liquid clouds observed during the research cruise show a liquid water path below the infra-red black body limit of approximately 50 g m−2. The majority of mixed-phase and ice clouds had an ice water path below 20 g m−2. Cloud properties are analysed with respect to cloud-top temperature and boundary layer structure. Changes in these parameters have little effect on the geometric thickness of liquid clouds while mixed-phase clouds during warm-air advection events are generally thinner than when such events were absent. Cloud-top temperatures are very similar for all mixed-phase clouds. However, more cases of lower cloud-top temperature were observed in the absence of warm-air advection. Profiles of liquid and ice water content are normalised with respect to cloud base and height. For liquid water clouds, the liquid water content profile reveals a strong increase with height with a maximum within the upper quarter of the clouds followed by a sharp decrease towards cloud top. Liquid water content is lowest for clouds observed below an inversion during warm-air advection events. Most mixed-phase clouds show a liquid water content profile with a very similar shape to that of liquid clouds but with lower maximum values during warm-air advection. The normalised ice water content profiles in mixed-phase clouds look different from that of liquid water content. They show a wider range in maximum values with lowest ice water content for clouds below an inversion and highest values for clouds above or extending through an inversion. The ice water content profile generally peaks at a height below the peak in the liquid water content profile – usually in the centre of the cloud, sometimes closer to cloud base, likely due to particle sublimation as the crystals fall through the cloud.

scholarly journals Ice multiplication from ice–ice collisions in the high Arctic: sensitivity to ice habit, rimed fraction, ice type and uncertainties in the numerical description of the process

2021 ◽  
Vol 21 (12) ◽  
pp. 9741-9760
Author(s):  
Georgia Sotiropoulou ◽  
Luisa Ickes ◽  
Athanasios Nenes ◽  
Annica M. L. Ekman
Keyword(s):  
High Arctic ◽  
The Arctic ◽  
Atmospheric Models ◽  
Ocean Study ◽  
Ice Water Content ◽  
Ice Multiplication ◽  
Ice Content ◽  
Cloud Ice ◽  
Mixed Phase Clouds ◽  
Ice Water

Abstract. Atmospheric models often fail to correctly reproduce the microphysical structure of Arctic mixed-phase clouds and underpredict ice water content even when the simulations are constrained by observed levels of ice nucleating particles. In this study we investigate whether ice multiplication from breakup upon ice–ice collisions, a process missing in most models, can account for the observed cloud ice in a stratocumulus cloud observed during the Arctic Summer Cloud Ocean Study (ASCOS) campaign. Our results indicate that the efficiency of this process in these conditions is weak; increases in fragment generation are compensated for by subsequent enhancement of precipitation and subcloud sublimation. Activation of collisional breakup improves the representation of cloud ice content, but cloud liquid remains overestimated. In most sensitivity simulations, variations in ice habit and prescribed rimed fraction have little effect on the results. A few simulations result in explosive multiplication and cloud dissipation; however, in most setups, the overall multiplication effects become substantially weaker if the precipitation sink is enhanced through cloud-ice-to-snow autoconversion. The largest uncertainty stems from the correction factor for ice enhancement due to sublimation included in the breakup parameterization; excluding this correction results in rapid glaciation, especially in simulations with plates. Our results indicate that the lack of a detailed treatment of ice habit and rimed fraction in most bulk microphysics schemes is not detrimental for the description of the collisional breakup process in the examined conditions as long as cloud-ice-to-snow autoconversion is considered.

In Situ Aircraft Measurements of the Vertical Distribution of Liquid and Ice Water Content in Midlatitude Mixed-Phase Clouds

2013 ◽  
Vol 52 (1) ◽  
pp. 269-279 ◽  
Author(s):  
Yoo-Jeong Noh ◽  
Curtis J. Seaman ◽  
Thomas H. Vonder Haar ◽  
Guosheng Liu
Keyword(s):  
Vertical Distribution ◽  
Water Content ◽  
Liquid Water ◽  
Mixed Phase ◽  
Water Fraction ◽  
Ice Water Content ◽  
Mixed Phase Clouds ◽  
Ice Water ◽  
The Vertical Distribution

AbstractThe vertical distribution of liquid and ice water content and their partitioning is studied using 34 cases of in situ measured microphysical properties in midlatitude mixed-phase clouds, with liquid water path ranging from near zero to ~248 g m−2, total water path ranging from near zero to ~562 g m−2, and cloud-top temperature ranging from −2° to −38°C. The 34 profiles were further divided into three cloud types depending on their vertical extents and altitudes. It is found that both the vertical distribution of liquid water within a cloud and the liquid water fraction (of total condensed water) as a function of temperature or relative position in a cloud layer are cloud-type dependent. In particular, it is found that the partitioning between liquid and ice water for midlevel shallow clouds is relatively independent on the vertical position within the cloud while it clearly depends on cloud mean temperature. For synoptic snow clouds, however, liquid water fraction increases with the decrease of altitude within the cloud. While the liquid water fraction in synoptic clouds also decreases with lowering temperature, its magnitude is only about 50% near 0°C.

scholarly journals Observed aerosol suppression of cloud ice in low-level Arctic mixed-phase clouds

2018 ◽  
Author(s):  
Matthew S. Norgren ◽  
Gijs de Boer ◽  
Matthew D. Shupe
Keyword(s):  
Water Content ◽  
Mixed Phase ◽  
Cloud Base ◽  
Low Level ◽  
Ice Water Content ◽  
Earth’S Climate ◽  
Ice Production ◽  
Mixed Phase Clouds ◽  
Ice Water ◽  
The Impact

Abstract. The interactions that occur between aerosols and a mixed-phase cloud system, and the subsequent alteration of the microphysical state of such clouds, is a problem that has yet to be well constrained. Advancing our understanding of aerosol-ice processes is necessary to determine the impact of natural and anthropogenic emissions on Earth’s climate and to improve our capability to predict future climate states. This paper deals specifically with how aerosols influence ice mass production in low-level Arctic mixed-phase clouds. In this study, a 9-year record of aerosol, cloud and atmospheric state properties is used to quantify aerosol influence on ice production in mixed-phase clouds. It is found that mixed-phase clouds present in a clean aerosol state have higher ice water content by a factor of 1.22 to 1.63 at cloud base than do similar clouds in cases with higher aerosol loading. We additionally analyze radar-derived mean Doppler velocities to better understand the drivers behind this relationship, and conclude that aerosol suppression of ice nucleation, together with reduced riming rates in polluted clouds are likely influences on the observed reductions in ice water content.

scholarly journals Representation by two climate models of the dynamical and diabatic processes involved in the development of an explosively deepening cyclone during NAWDEX

2021 ◽  
Vol 2 (1) ◽  
pp. 233-253
Author(s):  
David L. A. Flack ◽  
Gwendal Rivière ◽  
Ionela Musat ◽  
Romain Roehrig ◽  
Sandrine Bony ◽  
...  
Keyword(s):  
Diabatic Heating ◽  
Climate Models ◽  
Global Climate ◽  
Weather Forecast ◽  
Relative Vorticity ◽  
Global Climate Models ◽  
Mature Stage ◽  
The North ◽  
Upper Level ◽  
Ice Water

Abstract. The dynamical and microphysical properties of a well-observed cyclone from the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX), called the Stalactite cyclone and corresponding to intensive observation period 6, is examined using two atmospheric components (ARPEGE-Climat 6.3 and LMDZ6A) of the global climate models CNRM-CM6-1 and IPSL-CM6A, respectively. The hindcasts are performed in “weather forecast mode”, run at approximately 150–200 km (low resolution, LR) and approximately 50 km (high resolution, HR) grid spacings, and initialised during the initiation stage of the cyclone. Cyclogenesis results from the merging of two relative vorticity maxima at low levels: one associated with a diabatic Rossby vortex (DRV) and the other initiated by baroclinic interaction with a pre-existing upper-level potential vorticity (PV) cut-off. All hindcasts produce (to some extent) a DRV. However, the second vorticity maximum is almost absent in LR hindcasts because of an underestimated upper-level PV cut-off. The evolution of the cyclone is examined via the quasi-geostrophic ω equation which separates the diabatic heating component from the dynamical one. In contrast to some previous studies, there is no change in the relative importance of diabatic heating with increased resolution. The analysis shows that LMDZ6A produces stronger diabatic heating compared to ARPEGE-Climat 6.3. Hindcasts initialised during the mature stage of the cyclone are compared with airborne remote-sensing measurements. There is an underestimation of the ice water content in the model compared to the one retrieved from radar-lidar measurements. Consistent with the increased heating rate in LMDZ6A compared to ARPEGE-Climat 6.3, the sum of liquid and ice water contents is higher in LMDZ6A than ARPEGE-Climat 6.3 and, in that sense, LMDZ6A is closer to the observations. However, LMDZ6A strongly overestimates the fraction of super-cooled liquid compared to the observations by a factor of approximately 50.

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