scholarly journals Cloud Trails Past the Lesser Antilles

2015 ◽  
Vol 143 (4) ◽  
pp. 995-1017 ◽  
Author(s):  
Daniel J. Kirshbaum ◽  
Jonathan G. Fairman
Keyword(s):  
Wind Speed ◽  
Thermal Anomaly ◽  
Surface Fluxes ◽  
Lesser Antilles ◽  
Trade Wind ◽  
Trade Winds ◽  
Cold Pools ◽  
Wake Turbulence ◽  
Island Wake ◽  
One Year

Abstract Observations and cloud-resolving simulations of elongated cloud plumes (or “cloud trails”) past the Lesser Antilles islands in the Caribbean Sea are presented. Analysis of one year of visible satellite images reveals that each island forms cloud trails on 30%–40% of days, typically in the afternoon in response to diurnal island heating. On around 10% of days the cloud bands are very well organized, with lengths of and durations of min. Radiosonde analysis suggests that the well-organized events are favored by moderate-to-strong trade winds (6–10 m s−1) and stronger trade inversions. The simulated cloud trails, which are consistent with observations in their morphology and diurnal cycle, are organized by quasi-linear bands of thermally forced convergence within the heated island wake. They are sensitive to overland surface fluxes, inversion strength and height, terrain height, and trade-wind speed. While surface fluxes control the strength of the wake thermal circulations, the inversion controls precipitation and the disruption of cloud trails by subcloud cold pools. The impacts of terrain height and wind speed are multifaceted, including control over (i) the mechanical flow regime, (ii) the intensity of wake turbulence, (iii) the cloud-trail length, (iv) the wake thermal anomaly, and (v) elevated-heating effects (which strengthen the thermal convergence). Dimensional analysis is used to develop empirical scalings for the wake thermal circulation, which describe the suite of numerical sensitivity tests reasonably well.

scholarly journals One-year analysis of rain and rain erosivity in a tropical volcanic island from UHF wind profiler measurements

2013 ◽  
Vol 6 (2) ◽  
pp. 3249-3277 ◽  
Author(s):  
A. Réchou ◽  
M. Plu ◽  
B. Campistron ◽  
R. Decoupes
Keyword(s):  
Kinetic Energy ◽  
Rain Rate ◽  
Cold Front ◽  
Deep Convection ◽  
Trade Wind ◽  
Energy Fluxes ◽  
Trade Winds ◽  
Rainfall Events ◽  
The Mean ◽  
One Year

Abstract. La Réunion is a volcanic island in a tropical zone, which soil undergoes intense erosion. The possible contribution of rainfall to erosion is analyzed and quantified using one year of UHF radar profiler data located at sea level. Measurements of reflectivity, vertical and horizontal wind allow, with suitable assumptions, to determine raindrop vertical and horizontal energy fluxes, which are both essential parameters for erosion. After calibration of radar rain rates, one-year statistics between May 2009 to April 2010 allow to identify differences in rain vertical profiles depending on the season. During the cool dry season, the mean rain rate is less than 2.5 mm h−1 as high as 1.25 km and it decreases at higher altitudes due to the trade winds inversion. During the warm moist season, the mean rain rate is nearly uniform from ground up to 4 km, around 5 mm h−1. The dynamical and microphysical properties of rainfall events are investigated on three cases that are representative of meteorological events in La Réunion: summer deep convection, a cold front and a winter depression embedded in trade winds. For intense rainfall events, the rain rate deduced from the gamma function is in agreement with the rain rate deduced from the mere Marshall Palmer exponential relationship. For less intense events, the gamma function is necessary to represent rain distribution. The deep-convection event is associated to strong reflectivity reaching as high as 10 km, and strong negative vertical velocity. Wind shear is responsible for a deficiency of radar rain detection at the lower levels. During a cold front event, strong reflectivities reach the trade wind inversion (around 4 km high). The trade wind depression generates moderate rain only as high as 2 km. For all the altitudes, the horizontal kinetic energy fluxes are one order of magnitude stronger that than the vertical kinetic energy fluxes. A simple relationship between the reflectivity factor and vertical kinetic energy fluxes is found for each case study.

scholarly journals Effects of Trade Wind Strength on Airflow and Cloudiness over O‘ahu

2021 ◽  
Author(s):  
Feng Hsiao ◽  
Yi-Leng Chen ◽  
Hiep Van Nguyen ◽  
David Eugene Hitzl ◽  
Robert Ballard
Keyword(s):  
Sea Breeze ◽  
Windward Side ◽  
Trade Wind ◽  
Return Flow ◽  
Western Coast ◽  
Trade Winds ◽  
Flow Deceleration ◽  
Orographic Clouds ◽  
Island Wake ◽  
Orographic Cloud

AbstractSatellite observations and high-resolution modeling during July–August 2013 are used to study the effects of trade wind strength on island wake circulations and cloudiness over O‘ahu, Hawai‘i. O‘ahu is composed of two northwest–southeast orientated mountain ranges: the Wai‘anae Range (~1227 m) along the western leeside coast and the Ko‘olau Range (~944 m) along the eastern windward coast. At night, the flow deceleration of the incoming northeasterly trade winds on the eastern windward side is more significant when trades are stronger.In the afternoon hours, effective albedo and simulated cloud water are greater over the Ko‘olau Range when trades are stronger, and clouds are advected downstream by the trade winds aloft. Over the Wai‘anae Range, orographic clouds are more significant when trades are weaker due to less moisture removal by orographic precipitation over the Ko‘olau Range and the development of both upslope flow on the eastern slope and upslope/sea-breeze flow along the western coast, the latter of which brings in warm, moist air from the ocean. When trades are weaker, cloudiness off the western leeside coast is more extensive and originates from orographic cloud development over the Wai‘anae Range, which drifts downstream due to a combination of trade winds and the easterly return flow aloft. The latter is associated with the low-level sea-breeze/upslope flow.

scholarly journals Wintertime Easterly and Southeasterly Airflow in the ‘Alenuihāhā Channel, Hawaii

2020 ◽  
Vol 148 (4) ◽  
pp. 1337-1362 ◽  
Author(s):  
David Eugene Hitzl ◽  
Yi-Leng Chen ◽  
Feng Hsiao
Keyword(s):  
Wind Speed ◽  
Trade Wind ◽  
Trade Winds ◽  
Wind Speeds ◽  
Channel Exit ◽  
Wind Event ◽  
South Shore ◽  
Typical Summer ◽  
Wind Regimes ◽  
The Impact

Abstract During the wintertime, easterly (E) to southeasterly (SE) flow in the Hawaiian coastal waters is frequent. These wind regimes alter the location and magnitude of channel and tip jet accelerations and the orientation and horizontal extent of the wake zones from east-northeast (ENE) trade wind conditions. The differences are the result of changes in orographic blocking by the Big Island and Maui, with respect to the prevailing wind. During an E wind event, the fastest winds over the ‘Alenuihāhā Channel (>9 m s−1) occur in the channel exit with sinking of the inversion, which rises again downstream. Although the upstream wind speed is similar to typical summer ENE trade winds (7–8 m s−1), the maximum channel wind speed is 3–4 m s−1 slower in the exit. The SE flow is characterized by maximum (~6 m s−1) northeasterly (NE) channel winds along Maui’s south shore and at the channel exit. These winds are the result of orographic blocking on the eastern end of Maui as the northwestern tail of a tip jet off the northeastern coast of the Big Island impinges on Mount Haleakalā. Channel wind speeds are modulated by the speed and direction of this tip jet, which itself varies diurnally and throughout the approach of a midlatitude cold front. Removal of the Big Island shows how the tip jet speed and orientation modulate the pressure gradients and winds in the ‘Alenuihāhā Channel. Removal of the Maui County terrain reveals the impact of orographic blocking on the occurrence of channel winds off Maui’s south shore.

scholarly journals Differences between Nonprecipitating Tropical and Trade Wind Marine Shallow Cumuli

2016 ◽  
Vol 144 (2) ◽  
pp. 681-701 ◽  
Author(s):  
Virendra P. Ghate ◽  
Mark A. Miller ◽  
Ping Zhu
Keyword(s):  
Surface Fluxes ◽  
Cloud Base ◽  
Trade Wind ◽  
Cumulus Clouds ◽  
Wind Speeds ◽  
Lower Cloud ◽  
Observational Site ◽  
Velocity Scale ◽  
Atmospheric Radiation Measurement ◽  
The Mean

Abstract Marine nonprecipitating cumulus topped boundary layers (CTBLs) observed in a tropical and in a trade wind region are contrasted based on their cloud macrophysical, dynamical, and radiative structures. Data from the Atmospheric Radiation Measurement (ARM) observational site previously operating at Manus Island, Papua New Guinea, and data collected during the deployment of ARM Mobile Facility at the island of Graciosa, in the Azores, were used in this study. The tropical marine CTBLs were deeper, had higher surface fluxes and boundary layer radiative cooling, but lower wind speeds compared to their trade wind counterparts. The radiative velocity scale was 50%–70% of the surface convective velocity scale at both locations, highlighting the prominent role played by radiation in maintaining turbulence in marine CTBLs. Despite greater thicknesses, the chord lengths of tropical cumuli were on average lower than those of trade wind cumuli, and as a result of lower cloud cover, the hourly averaged (cloudy and clear) liquid water paths of tropical cumuli were lower than the trade wind cumuli. At both locations ~70% of the cloudy profiles were updrafts, while the average amount of updrafts near cloud base stronger than 1 m s−1 was ~22% in tropical cumuli and ~12% in the trade wind cumuli. The mean in-cloud radar reflectivity within updrafts and mean updraft velocity was higher in tropical cumuli than the trade wind cumuli. Despite stronger vertical velocities and a higher number of strong updrafts, due to lower cloud fraction, the updraft mass flux was lower in the tropical cumuli compared to the trade wind cumuli. The observations suggest that the tropical and trade wind marine cumulus clouds differ significantly in their macrophysical and dynamical structures.

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.

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>

scholarly journals Wind speed modeling based on measurement data to predict future wind speed with modified Rayleigh model

2021 ◽  
Vol 12 (3) ◽  
pp. 1823
Author(s):  
Suwarno Suwarno ◽  
Rohana Rohana
Keyword(s):  
Wind Speed ◽  
Measurement Data ◽  
Rayleigh Distribution ◽  
Scale Factor ◽  
Percentage Error ◽  
Monthly Data ◽  
Wind Speeds ◽  
Wind Characteristics ◽  
One Year ◽  
The Many

The development of modeling wind speed plays a very important in helping to obtain the actual wind speed data for the benefit of the power plant planning in the future. The wind speed in this paper is obtained from a PCE-FWS 20 type measuring instrument with a duration of 30 minutes which is accumulated into monthly data for one year (2019). Despite the many wind speed modeling that has been done by researchers. Modeling wind speeds proposed in this study were obtained from the modified Rayleigh distribution. In this study, the Rayleigh scale factor (<em>C<sub>r</sub></em>) and modified Rayleigh scale factor (<em>C<sub>m</sub></em>) were calculated. The observed wind speed is compared with the predicted wind characteristics. The data fit test used correlation coefficient (R<sup>2</sup>), root means square error (RMSE), and mean absolute percentage error (MAPE). The results of the proposed modified Rayleigh model provide very good results for users.

Application of SVEN model to estimate evapotranspiration on a coffee plantation using MODIS and Sentinel products.

2021 ◽  
Author(s):  
Ana María Durán-Quesada ◽  
Ioanna Pateromichelaki ◽  
Mónica García ◽  
Sheng Wang ◽  
Yolande Serra ◽  
...  
Keyword(s):  
Southern Oscillation ◽  
National Income ◽  
Surface Fluxes ◽  
Coffee Plantation ◽  
Diurnal Variability ◽  
Coffee Plantations ◽  
Soil Moisture Sensors ◽  
Use Efficiency ◽  
One Year ◽  
Soil Measurements

&lt;div&gt; &lt;p&gt;Warming conditions represent a threat to food security and livelihood in countries in which agriculture is an important share of the national income. Central America is regarded as a climate change hotspot where significant changes in temperature and rainfall have been projected. Coffee is one of the most traditional crops in the area, with Costa Rican coffee recognized worldwide for its quality. However, increasing temperatures and rainfall extremes will likely compromise coffee plantations. A similar challenge has already been faced by farmers on interannual time scales related to the El Ni&amp;#241;o-Southern Oscillation phenomena, which is associated with yield disruptions and the spread of the coffee rust. A better understanding of the weather and climate dependency of coffee crops is needed to develop water use efficiency strategies for farms. To this end, the present study centers on the integration of long-term meteorological records and a set of measurements that cover the soil-plant-atmosphere continuum. Surface fluxes derived using the eddy covariance technique and the deployment of soil moisture sensors are combined to evaluate the performance of the Soil Vegetation Energy TraNsfer (SVEN) model. One year of micrometeorological and soil measurements in a sun-exposed coffee plantation is used to assess the skills of the SVEN model using a scheme based on MODIS and Sentinel derived products. The aim of this work is to evaluate the skills of the SVEN model to reproduce the intraseasonal seasonal and diurnal variability of evapotranspiration. Given the size of Costa Rica and the scale of the crops, satellite products are often considered of limited use. Nevertheless, given the strong need, the goal of this project is to provide a detailed evaluation of the use of these products in models and support strategies that could expand the use of satellite retrievals in areas currently considered marginal.&lt;/p&gt; &lt;/div&gt;

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