scholarly journals Mechanical Forcing of Convection by Cold Pools: Collisions and Energy Scaling

2020 ◽  
Vol 12 (11) ◽  
Author(s):  
Bettina Meyer ◽  
Jan O. Haerter
Keyword(s):  
Cold Pools ◽  
Energy Scaling ◽  
Mechanical Forcing

Tracking a Long-Lasting Outer Tropical Cyclone Rainband: Origin and Convective Transformation

2019 ◽  
Vol 76 (10) ◽  
pp. 3267-3283 ◽  
Author(s):  
Cheng-Ku Yu ◽  
Che-Yu Lin ◽  
Jhang-Shuo Luo
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Radial Distance ◽  
Vertical Shear ◽  
Convective Precipitation ◽  
Squall Line ◽  
Mature Stage ◽  
Clear Trend ◽  
Dynamical Interaction ◽  
Cold Pools

Abstract This study used radar and surface observations to track a long-lasting outer tropical cyclone rainband (TCR) of Typhoon Jangmi (2008) over a considerable period of time (~10 h) from its formative to mature stage. Detailed analyses of these unique observations indicate that the TCR was initiated on the eastern side of the typhoon at a radial distance of ~190 km as it detached from the upwind segment of a stratiform rainband located close to the inner-core boundary. The outer rainband, as it propagated cyclonically outward, underwent a prominent convective transformation from generally stratiform precipitation during the earlier period to highly organized, convective precipitation during its mature stage. The transformation was accompanied by a clear trend of surface kinematics and thermodynamics toward squall-line-like features. The observed intensification of the rainband was not simply related to the spatial variation of the ambient CAPE or potential instability; instead, the dynamical interaction between the prerainband vertical shear and cold pools, with progression toward increasingly optimal conditions over time, provides a reasonable explanation for the temporal alternation of the precipitation intensity. The increasing intensity of cold pools was suggested to play an essential role in the convective transformation for the rainband. The propagation characteristics of the studied TCR were distinctly different from those of wave disturbances frequently documented within the cores of tropical cyclones; however, they were consistent with the theoretically predicted propagation of convectively generated cold pools. The convective transformation, as documented in the present case, is anticipated to be one of the fundamental processes determining the evolving and structural nature of outer TCRs.

scholarly journals Cold Pools as Conveyor Belts of Moisture

2020 ◽  
Author(s):  
Herman F. Fuglestvedt ◽  
Haerter O Haerter
Keyword(s):  
Cold Pools ◽  
Conveyor Belts

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.

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.

Pulse energy scaling of multipass spectral broadening beyond 100 mJ

2021 ◽  
Author(s):  
Martin Kaumanns ◽  
Dmitrii Kormin ◽  
Thomas Nubbemeyer ◽  
Vladimir Pervak ◽  
Stefan Karsch
Keyword(s):  
Pulse Energy ◽  
Spectral Broadening ◽  
Energy Scaling

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>

Atmospheric Cold Pools and Their Influence on Sea Surface Temperature in the Bay of Bengal

2021 ◽  
Vol 126 (9) ◽  
Author(s):  
M. S. Girishkumar ◽  
Jofia Joseph ◽  
M. J. McPhaden ◽  
E. Pattabhi Ram Rao
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Bay Of Bengal ◽  
Sea Surface ◽  
Cold Pools

FESST@HH 2020: Ein dichtes Messnetz als Lupe für die Struktur konvektiver Cold Pools

2021 ◽  
Author(s):  
Bastian Kirsch ◽  
Cathy Hohenegger ◽  
Daniel Klocke ◽  
Felix Ament
Keyword(s):  
Cold Pool ◽  
Cold Pools ◽  
O 10

<p>Cold Pools sind mesoskalige Gebiete kalter und dichter Luftmassen, die durch Verdunstung von Hydrometeoren unterhalb regnender Wolken entstehen. Während die kalte Luft absinkt und sich als Dichteströmung an der Erdoberfläche ausbreitet, löst sie durch Hebung an ihrer Vorderseite häufig neue Konvektion aus oder forciert den Übergang von flacher zu tiefer Konvektion. Viele modellbasierte Arbeiten belegen die Bedeutung von Cold Pools für die Organisation von Konvektion. Operationelle Messnetze mit einer typischen Maschenweite von 25 km hingegen sind blind für sub-mesoskalige (O(100) m — O(10) km) Prozesse wie Cold Pools und erlauben somit weder die Untersuchung noch die Validierung ihrer raum-zeitlichen Struktur.</p> <p>Im Rahmen der Messkampagne FESST@HH wurde von Juni bis August 2020 im Großraum Hamburg (50 km × 35 km) ein dichtes Netz bestehend aus 103 meteorologischen Messstationen betrieben. Das Rückgrat des Messnetzes bildeten 82 eigens für diesen Zweck entwickelte und gebaute APOLLO-Stationen (Autonomous cold POoL LOgger), die Lufttemperatur und -druck mit trägheitsarmen Sensoren in sekündlicher Auflösung messen. Das Netzwerk wurde mit 21 Wetterstationen ergänzt, die zusätzlich Luftfeuchte, Windgeschwindigkeit und Niederschlag in 10-sekündiger Auflösung aufzeichnen und auf kommerziellen Sensoren basieren. Ein besonderes Merkmal von FESST@HH ist, dass die Durchführung der Kampagne während der COVID19-Pandemie nur durch eine große Zahl Freiwilliger ermöglicht wurde, die kurzfristig Messstandorte bereitgestellt und die Betreuung der Instrumente unterstützt haben.</p> <p>Wir präsentieren die neuartigen Messinstrumente und den Datensatz der FESST@HH-Kampagne (DOI: 10.25592/UHHFDM.8966). Ein Fallbeispiel zeigt, dass das dichte Messnetz in der Lage ist sowohl die horizontale Heterogenität des Temperaturfeldes innerhalb eines Cold Pools als auch seine Größe und Ausbreitungsgeschwindigkeit während verschiedener Phasen des Lebenszyklus abzubilden. Darüber hinaus erlauben die Messungen einen neuen Blick auf weitere Quellen sub-mesoskaliger Variabilität wie die nächtliche städtische Wärmeinsel und die Variation turbulenter Temperaturfluktuationen als Ausdruck charakteristischer Standorteigenschaften.</p>

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