scholarly journals The genesis of Hurricane Nate and its interaction with a nearby environment of very dry air

2017 ◽  
Vol 17 (17) ◽  
pp. 10349-10366 ◽  
Author(s):  
Blake Rutherford ◽  
Timothy Dunkerton ◽  
Michael Montgomery ◽  
Scott Braun
Keyword(s):  
Primary Source ◽  
Stable And Unstable Manifolds ◽  
Dry Air ◽  
African Easterly Wave ◽  
Easterly Wave ◽  
Moisture Influence ◽  
Vorticity Transport ◽  
Lagrangian Frame ◽  
Thermodynamic Processes ◽  
Frontal Boundary

Abstract. The interaction of a tropical disturbance with its environment is thought to play an important role in whether a disturbance will develop or not. Most developing disturbances are somewhat protected from the intrusion of environmental dry air at mid-levels. For African easterly wave (AEW) disturbances, the protective boundary is approximated by closed streamlines in the wave-relative frame, and their interior is called the wave pouch. The dynamic and thermodynamic processes of spin-up occur inside the pouch. In this study, we define the kinematic boundaries for a non-AEW disturbance in the Bay of Campeche that originated along a sharp frontal boundary in a confluent region of low pressure. We examine these boundaries during the genesis of Hurricane Nate (2011) to show how a pouch boundary on isobaric levels in the Lagrangian frame may allow for some transport into the pouch along the frontal boundary while still protecting the innermost development region. This result illustrates a generic property of weakly unsteady flows, including the time-dependent critical layer of AEWs, that lateral exchange of air occurs along a segment of the boundary formed by the instantaneous, closed translating streamlines. Transport in the Lagrangian frame is simplest when measured with respect to the stable and unstable manifolds of a hyperbolic trajectory, which are topologically invariant. In this framework, an exact analysis of vorticity transport identifies the primary source as the advection of vorticity through the entrainment and expulsion of bounded material regions called lobes. We also show how these Lagrangian boundaries impact the concentration of moisture, influence convection, and contribute to the pouch vertical structure.

scholarly journals The genesis of Hurricane Nate and its interaction with a nearby environment of very dry air

2017 ◽  
Author(s):  
Blake Rutherford ◽  
Timothy Dunkerton ◽  
Michael Montgomery ◽  
Scott Braun
Keyword(s):  
Stable And Unstable Manifolds ◽  
Dry Air ◽  
African Easterly Wave ◽  
Easterly Wave ◽  
Moisture Influence ◽  
Vorticity Transport ◽  
Lagrangian Boundary ◽  
Lagrangian Frame ◽  
Thermodynamic Processes ◽  
Frontal Boundary

Abstract. The interaction of a tropical disturbance with its environment is thought to play an important role in whether a disturbance will develop of not. Most developing disturbances are somewhat protected from the intrusion of environmental dry air at mid-levels. For African easterly wave (AEW) disturbances, the protective boundary is approximated by closed streamlines in the wave-relative frame, and their interior is called the wave-pouch. The dynamic and thermodynamic processes of spin-up occur inside the pouch. In this study we define the kinematic boundaries for a non-AEW disturbance in the Bay of Campeche that originated along a sharp frontal boundary in a confluent region of low pressure. We examine these boundaries during the genesis of Hurricane Nate (2011) to show how a layer-wise pouch boundary in the Lagrangian frame may allow for some transport into the pouch along the frontal boundary while still protecting the innermost development region. This result illustrates a generic property of weakly unsteady flows, including the time-dependent critical-layer of AEWs, that lateral exchange of air occurs along a segment of the boundary formed by the instantaneous, closed translating streamlines. Transport in the Lagrangian frame is simplest when measured with respect to the stable and unstable manifolds of a hyperbolic trajectory, which are topologically invariant. In this framework, an exact analysis of vorticity transport identifies two sources; i) the advection of vorticity through the entrainment and expulsion of bounded material regions called lobes, and ii) the baroclinic contribution of vorticity transport through the tilting mechanism across the Lagrangian boundary. We also show how these Lagrangian boundaries impact the concentration of moisture, influence convection, and contribute to the pouch vertical structure.

Future characteristics of African Easterly Wave tracks

2018 ◽  
Vol 52 (9-10) ◽  
pp. 5567-5584
Author(s):  
Allison Lynn Brannan ◽  
Elinor R. Martin
Keyword(s):  
African Easterly Wave ◽  
Easterly Wave

scholarly journals The interaction between moist diabatic processes and the atmospheric circulation in African Easterly Wave propagation

2017 ◽  
Vol 143 (709) ◽  
pp. 3207-3227 ◽  
Author(s):  
Lorenzo Tomassini ◽  
Douglas J. Parker ◽  
Alison Stirling ◽  
Caroline Bain ◽  
Catherine Senior ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Atmospheric Circulation ◽  
African Easterly Wave ◽  
Easterly Wave ◽  
Diabatic Processes

scholarly journals Meteorological Analysis of Floods in Ghana

2020 ◽  
Vol 2020 ◽  
pp. 1-14 ◽  
Author(s):  
S. O. Ansah ◽  
M. A. Ahiataku ◽  
C. K. Yorke ◽  
F. Otu-Larbi ◽  
Bashiru Yahaya ◽  
...  
Keyword(s):  
Heavy Rainfall ◽  
Wrf Model ◽  
Extreme Rainfall ◽  
Economic Loss ◽  
Daily Maximum ◽  
Maximum Rainfall ◽  
African Easterly Wave ◽  
Easterly Wave ◽  
Forest Region ◽  
National Disaster

The first episodes of floods caused by heavy rainfall during the major rainy season in 2018 occurred in Accra (5.6°N and 0.17°W), a coastal town, and Kumasi (6.72°N and 1.6°W) in the forest region on the 18th and 28th of June, respectively. We applied the Weather Research and Forecasting (WRF) model to investigate and examine the meteorological dynamics, which resulted in the extreme rainfall and floods that caused 14 deaths, 34076 people being displaced with damaged properties, and economic loss estimated at $168,289 for the two cities according to the National Disaster Management Organization (NADMO). The slow-moving thunderstorms lasted for about 8 hours due to the weak African Easterly Wave (AEW) and Tropical Easterly Jet (TEJ). Results from the analysis showed that surface pressures were low with significant amount of moisture influx aiding the thunderstorms intensification, which produced 90.1 mm and 114.6 mm of rainfall over Accra and Kumasi, respectively. We compared the rainfall amount from this event to the historical rainfall data to investigate possible changes in rainfall intensities over time. A time series of annual daily maximum rainfall (ADMR) showed an increasing trend with a slope of 0.45 over Accra and a decreasing trend and a slope of –0.07 over Kumasi. The 95th percentile frequencies of extreme rainfall with thresholds of 45.10 mm and 42.16 mm were analyzed for Accra and Kumasi, respectively, based on the normal distribution of rainfall. Accra showed fewer days with more heavy rainfall, while Kumasi showed more days with less heavy rainfalls.

Observations and Predictability of a Nondeveloping Tropical Disturbance over the Eastern Atlantic

2018 ◽  
Vol 146 (9) ◽  
pp. 3079-3096 ◽  
Author(s):  
Alan Brammer ◽  
Chris D. Thorncroft ◽  
Jason P. Dunion
Keyword(s):  
Deep Convection ◽  
Recirculation Region ◽  
Tropical Cyclogenesis ◽  
Short Term ◽  
Ensemble Forecasts ◽  
Dry Air ◽  
Easterly Wave ◽  
Closed Circulation ◽  
West African Coast ◽  
Favorable Conditions

Abstract A strong African easterly wave (AEW) left the West African coast in early September 2014 and operational global numerical forecasts suggested a potential for rapid tropical cyclogenesis of this disturbance in the eastern Atlantic, despite the presence of a large region of dry air northwest of the disturbance. Analysis and in situ observations show that after leaving the coast, the closed circulation associated with the AEW trough was not well aligned vertically, and therefore, low-level or midlevel dry air was advected below or above, respectively, areas of closed circulation. GPS dropwindsonde observations highlight the dry air undercutting the midlevel recirculation region in the southwestern quadrant. This advection of dry air constrains the spatial extent of deep convection within the AEW trough, leading to the vortex decaying. As the column continues to be displaced horizontally, losing vertical alignment, this enables increased horizontal advection of dry air into the system further limiting convective activity. Ensemble forecasts indicate that short-term errors in precipitation rate and vorticity generation can lead to an over intensified and well-aligned vortex, which then interacts less with the unfavorable environment, allowing for further convection and intensification. The stronger vortex provides more favorable conditions for precipitation through a more vertically coherent closed circulation and thus a positive feedback loop is initiated. The short-term forecasts of precipitation were shown to be sensitive to lower-tropospheric moisture anomalies around the AEW trough through ensemble sensitivity analysis from Global Ensemble Forecast System real-time forecasts.

scholarly journals Genesis of Hurricane Julia (2010) within an African Easterly Wave: Developing and Nondeveloping Members from WRF–LETKF Ensemble Forecasts

2014 ◽  
Vol 71 (7) ◽  
pp. 2763-2781 ◽  
Author(s):  
Stefan F. Cecelski ◽  
Da-Lin Zhang ◽  
Takemasa Miyoshi
Keyword(s):  
Surface Pressure ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Ensemble Forecasts ◽  
Upper Troposphere ◽  
African Easterly Wave ◽  
Easterly Wave ◽  
Mesoscale Convective ◽  
Rossby Radius Of Deformation ◽  
Faster Development

Abstract In this study, the predictability of and parametric differences in the genesis of Hurricane Julia (2010) are investigated using 20 mesoscale ensemble forecasts with the finest resolution of 1 km. Results show that the genesis of Julia is highly predictable, with all but two members undergoing genesis. Despite the high predictability, substantial parametric differences exist between the stronger and weaker members. Notably, the strongest-developing member exhibits large upper-tropospheric warming within a storm-scale outflow during genesis. In contrast, the nondeveloping member has weak and more localized warming due to inhibited convective development and a lack of a storm-scale outflow. A reduction in the Rossby radius of deformation in the strongest member aids in the accumulation of the warmth, while little contraction takes place in the nondeveloping member. The warming in the upper troposphere is responsible for the development of meso-α-scale surface pressure falls and a meso-β surface low in the strongest-developing member. Such features fail to form in the nondeveloping member as weak upper-tropospheric warming is unable to induce meaningful surface pressure falls. Cloud ice content is nearly doubled in the strongest member as compared to its nondeveloping counterparts, suggesting the importance of depositional heating of the upper troposphere. It is found that the stronger member undergoes genesis faster due to the lack of convective inhibition near the African easterly wave (AEW) pouch center prior to genesis. This allows for the faster development of a mesoscale convective system and storm-scale outflow, given the already favorable larger-scale conditions.

Internal processes within the African Easterly Wave system

2014 ◽  
Vol 141 (689) ◽  
pp. 1121-1136 ◽  
Author(s):  
D. Emmanuel Poan ◽  
Jean-Philippe Lafore ◽  
Romain Roehrig ◽  
Fleur Couvreux
Keyword(s):  
Wave System ◽  
African Easterly Wave ◽  
Easterly Wave
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