scholarly journals The Interaction between African Easterly Waves and Different Types of Deep Convection and Its Influence on Atlantic Tropical Cyclones

Atmosphere ◽  
2021 ◽  
Vol 13 (1) ◽  
pp. 5
Author(s):  
Bantwale D. Enyew ◽  
Ademe Mekonnen
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
African Easterly Waves ◽  
Large Area ◽  
Easterly Waves ◽  
Past Work ◽  
Development Region ◽  
Different Types ◽  
Tightly Coupled ◽  
Cumulus Congestus

This study revisited the association of African easterly waves (AEWs) to Atlantic tropical cyclone (TC) development using weather states (WSs) from the International Satellite Cloud Climatology Project, National Hurricane Center best track hurricane data (HURDAT2), and reanalysis products. The WS data are used as a proxy for two different types of deep convection. This study covers July–October 1984–2009. Statistical analysis based on HURDAT2 and objectively tracked AEWs has shown that a small fraction (~20%) of the AEWs that propagate from Africa serve as TC precursors. About 80% of the AEWs from the continent were non-developing. As in the past work, our study showed an important difference between developing and non-developing AEWs. Composites based on developing AEWs revealed well-organized large scale deep convection (one type, composed of mesoscale systems and thick anvil clouds) is tightly coupled to the AEW trough, while scattered, less well-organized deep convection (second type, isolated cumulonimbus and cumulus congestus clouds) dominated a large area downstream of the developing AEW trough. Developing AEWs propagate westwards while strengthening. In contrast, non-developing AEWs showed that the peak well-organized deep convection is located either behind (to the east of) or far ahead (to the west) of the AEW trough (peaks values are not in close proximity). Moreover, well-organized deep convections associated with non-developing AEWs were weaker than those associated with developing AEWs. The results indicated that convective activity ahead of the non-developing AEWs is weak. Positive relative humidity (RH) anomalies dominate the area around AEWs and downstream over the main TC development region. In contrast, negative RH dominated the main TC development region ahead of non-developing AEWs, suggesting an unfavorable environment downstream of the AEWs. The results also showed that developing AEWs maintained stronger features in the lower and middle troposphere, while non-developing AEWs exhibited weaker structures, in agreement with past work. (Supplemental information related to this paper is available at the journal’s website of this edition).

Probabilistic discrimination between large-scale environments of intensifying and decaying African Easterly Waves

2010 ◽  
Vol 36 (7-8) ◽  
pp. 1379-1401 ◽  
Author(s):  
Paula A. Agudelo ◽  
Carlos D. Hoyos ◽  
Judith A. Curry ◽  
Peter J. Webster
Keyword(s):  
Large Scale ◽  
African Easterly Waves ◽  
Easterly Waves

Simulations of the West African Monsoon with a Superparameterized Climate Model. Part II: African Easterly Waves

2014 ◽  
Vol 27 (22) ◽  
pp. 8323-8341 ◽  
Author(s):  
Rachel R. McCrary ◽  
David A. Randall ◽  
Cristiana Stan
Keyword(s):  
General Circulation ◽  
Climate Model ◽  
Deep Convection ◽  
West African Monsoon ◽  
General Circulation Models ◽  
African Easterly Waves ◽  
Climate System Model ◽  
Easterly Waves ◽  
Cloud Resolving Model ◽  
The Waves

Abstract The relationship between African easterly waves and convection is examined in two coupled general circulation models: the Community Climate System Model (CCSM) and the “superparameterized” CCSM (SP-CCSM). In the CCSM, the easterly waves are much weaker than observed. In the SP-CCSM, a two-dimensional cloud-resolving model replaces the conventional cloud parameterizations of CCSM. Results show that this allows for the simulation of easterly waves with realistic horizontal and vertical structures, although the model exaggerates the intensity of easterly wave activity over West Africa. The simulated waves of SP-CCSM are generated in East Africa and propagate westward at similar (although slightly slower) phase speeds to observations. The vertical structure of the waves resembles the first baroclinic mode. The coupling of the waves with convection is realistic. Evidence is provided herein that the diabatic heating associated with deep convection provides energy to the waves simulated in SP-CCSM. In contrast, horizontal and vertical structures of the weak waves in CCSM are unrealistic, and the simulated convection is decoupled from the circulation.

The Potential Vorticity Structure and Dynamics of African Easterly Waves

2020 ◽  
Vol 77 (3) ◽  
pp. 871-890 ◽  
Author(s):  
James O. H. Russell ◽  
Anantha Aiyyer
Keyword(s):  
Potential Vorticity ◽  
Deep Convection ◽  
Wave Structure ◽  
Wave Model ◽  
Tropical Cyclogenesis ◽  
African Easterly Waves ◽  
Moist Convection ◽  
Easterly Waves ◽  
Stratiform Clouds ◽  
Diabatic Forcing

Abstract The dynamics of African easterly waves (AEWs) are investigated from the perspective of potential vorticity (PV) using data from global reanalysis projects. To a leading order, AEW evolution is governed by four processes: advection of the wave-scale PV by background flow, advection of background PV by the AEW, diabatic forcing due to wave-scale moist convection, and coupling between the wave and background diabatic forcing. Moist convection contributes significantly to the growth of AEWs in the midtroposphere, and to both growth and propagation of AEWs near the surface. The former is associated with stratiform clouds while the latter with deep convection. Moist convection helps maintain a more upright AEW PV column against the background shear, which makes the wave structure conducive for tropical cyclogenesis. It is also argued that—contrary to the hypothesis in some prior studies—the canonical diabatic Rossby wave model is likely not applicable to AEWs.

scholarly journals Shallow and Deep Latent Heating Modes over Tropical Oceans Observed with TRMM PR Spectral Latent Heating Data

2010 ◽  
Vol 23 (8) ◽  
pp. 2030-2046 ◽  
Author(s):  
Yukari N. Takayabu ◽  
Shoichi Shige ◽  
Wei-Kuo Tao ◽  
Nagio Hirota
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Three Dimensional ◽  
Tropical Rainfall Measuring Mission ◽  
Radiative Heating ◽  
Latent Heating ◽  
Tropical Oceans ◽  
Trmm Precipitation ◽  
Subtropical Oceans ◽  
Cumulus Congestus

Abstract Three-dimensional distributions of the apparent heat source (Q1) − radiative heating (QR) estimated from Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) utilizing the spectral latent heating (SLH) algorithm are analyzed. Mass-weighted and vertically integrated Q1 − QR averaged over the tropical oceans is estimated as ∼72.6 J s−1 (∼2.51 mm day−1) and that over tropical land is ∼73.7 J s−1 (∼2.55 mm day−1) for 30°N–30°S. It is shown that nondrizzle precipitation over tropical and subtropical oceans consists of two dominant modes of rainfall systems: deep systems and congestus. A rough estimate of the shallow-heating contribution against the total heating is about 46.7% for the average tropical oceans, which is substantially larger than the 23.7% over tropical land. Although cumulus congestus heating linearly correlates with SST, deep-mode heating is dynamically bounded by large-scale subsidence. It is notable that a substantial amount of rain, as large as 2.38 mm day−1 on average, is brought from congestus clouds under the large-scale subsiding circulation. It is also notable that, even in the region with SSTs warmer than 28°C, large-scale subsidence effectively suppresses the deep convection, with the remaining heating by congestus clouds. The results support that the entrainment of mid–lower-tropospheric dry air, which accompanies the large-scale subsidence, is the major factor suppressing the deep convection. Therefore, a representation of the realistic entrainment is very important for proper reproduction of precipitation distribution and the resultant large-scale circulation.

On the Atmospheric Regulation of the Growth of Moderate to Deep Cumulonimbus in a Tropical Environment

2014 ◽  
Vol 71 (3) ◽  
pp. 1105-1120 ◽  
Author(s):  
Vickal V. Kumar ◽  
Alain Protat ◽  
Christian Jakob ◽  
Peter T. May
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Atmospheric Conditions ◽  
Wet Season ◽  
Cumulus Clouds ◽  
Significant Difference ◽  
The Hours ◽  
Using Data ◽  
Cumulus Congestus ◽  
Rain Rates

Abstract Some cumulus clouds with tops between 3 and 7 km (Cu3km–7km) remain in this height region throughout their lifetime (congestus) while others develop into deeper clouds (cumulonimbus). This study describes two techniques to identify the congestus and cumulonimbus cloud types using data from scanning weather radar and identifies the atmospheric conditions that regulate these two modes. A two-wet-season cumulus cloud database of the Darwin C-band polarimetric radar is analyzed and the two modes are identified by examining the 0-dBZ cloud-top height (CTH) of the Cu3km–7km cells over a sequence of radar scans. It is found that ~26% of the classified Cu3km–7km population grow into cumulonimbus clouds. The cumulonimbus cells exhibit reflectivities, rain rates, and drop sizes larger than the congestus cells. The occurrence frequency of cumulonimbus cells peak in the afternoon at ~1500 local time—a few hours after the peak in congestus cells. The analysis of Darwin International Airport radiosonde profiles associated with the two types of cells shows no noticeable difference in the thermal stability rates, but a significant difference in midtropospheric (5–10 km) relative humidity. Moister conditions are found in the hours preceding the cumulonimbus cells when compared with the congestus cells. Using a moisture budget dataset derived for the Darwin region, it is shown that the existence of cumulonimbus cells, and hence deep convection, is mainly determined by the presence of the midtroposphere large-scale upward motion and not merely by the presence of congestus clouds prior to deep convection. This contradicts the thermodynamic viewpoint that the midtroposphere moistening prior to deep convection is solely due to the preceding cumulus congestus cells.

Favorable monsoon environment over eastern Africa for subsequent tropical cyclogenesis of African easterly waves

2021 ◽  
Author(s):  
Kelly M. Núñez Ocasio ◽  
Alan Brammer ◽  
Jenni L. Evans ◽  
George S. Young ◽  
Zachary L. Moon
Keyword(s):  
Large Scale ◽  
West African Monsoon ◽  
Eastern Africa ◽  
Tropical Cyclogenesis ◽  
African Easterly Waves ◽  
Easterly Waves ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Vertically Aligned ◽  
Somali Jet

AbstractEastern Africa is a common region of African easterly wave (AEW) onset and AEW early-life. How the large-scale environment over east Africa relates to the likelihood of an AEW subsequently undergoing tropical cyclogenesis in a climatology has not been documented. This study addresses the following hypothesis: AEWs that undergo tropical cyclogenesis (i.e., developing AEWs) initiate and propagate under a more favorable monsoon large-scale environment over eastern Africa when compared to non-developing AEWs. Using a 21-year August-to-September (1990-2010) climatology of AEWs, differences in the large-scale environment between developers and non-developers are identified and are propose to be used as key predictors of subsequent tropical cyclone formation and could informtropical cyclogenesis prediction. TC precursors when compared to non-developing AEWs experience: an anomalously active West African Monsoon, stronger northerly flow, more intense zonal Somali jet, anomalous convergence over the Marrah Mountains (region of AEW forcing), and a more intense and elongated African easterly jet (AEJ). These large-scale conditions are linked to near-trough attributes of developing AEWs which favor more moisture ingestion, vertically aligned circulation, a stronger initial 850-hPa vortex, deeper wave pouch, and arguably more AEW and Mesoscale convective systems interactions. AEWs that initiate over eastern Africa and cross the west coast of Africa are more likely to undergo tropical cyclogenesis than those initiating over central or west Africa. Developing AEWs are more likely to be southern-track AEWs than non-developing AEWs.

Development of a Customized Wireless Sensor System for Large-Scale Spatial Structures and Its Applications in Two Cases

2016 ◽  
Vol 16 (04) ◽  
pp. 1640017 ◽  
Author(s):  
Yanbin Shen ◽  
Pengcheng Yang ◽  
Yaozhi Luo
Keyword(s):  
Large Scale ◽  
Hardware Design ◽  
Digital Signal ◽  
Sensor Nodes ◽  
Sensor System ◽  
Wireless Sensor ◽  
Electromagnetic Properties ◽  
Spatial Structures ◽  
Large Area ◽  
Different Types

In this paper, a customized wireless sensor system (WSS) for structural health monitoring is developed toward large-scale spatial structures. Spatial structures are widely used in large public buildings which generally house thousands of people, therefore the safety of the buildings is a major concern for structural engineers. One of the characteristics of spatial structures is their steel construction and the material is homogeneous throughout. So the strain is commonly the most distinct parameter to indicate status of the structure. Another characteristic of spatial structures is their large-area scale, which brings problem for traditional wired monitoring systems, so an effective wireless sensor network (WSN) for structural monitoring is in urgent demand. Considering those features, the WSS development mainly focused on the sensor selection, hardware design and network customization. In this paper, a vibrating wire sensor is selected for strain measurement because of its stable, durable and anti-electromagnetic properties. For other parameters measurement, some commercial sensor products with digital signal output are adopted. Following the principle of modularization and extendibility, the hardware design is mainly based on the realization of several functional modules. All along, energy efficiency and measurement accuracy are the core design objective. The WSN is classified into four different types of topologies from basic to complex ones. They all have the common working mechanism, namely the collected data transfers via several relay from sensor nodes to sink nodes. Different types of networks are to be customized according to the configuration and scale of different structures. Finally, two typical applications are discussed in detail to verify the feasibility of the system. It can be concluded that the customized WSS is effective and durable, and well satisfies the requirement of structural status monitoring for large-scale spatial structures. Collected data have also shown that the structural stress variation is obvious under the effect of construction process and some other factors.

scholarly journals Wet Days in the Dry Quarter of the Alcântara Launch Center Region: Observational Features

2019 ◽  
Author(s):  
Paulo César Silva da Costa ◽  
Marcos Daisuke Oyama ◽  
Rosa de Fátima Cruz Marques
Keyword(s):  
Large Scale ◽  
Daily Precipitation ◽  
Weather Forecasting ◽  
Deep Convection ◽  
Longwave Radiation ◽  
Heavy Precipitation ◽  
Large Area ◽  
Launch Site ◽  
Precipitation Total ◽  
Precipitation Events

Precipitation events are infrequent in the dry quarter (SON) of the Alcântara Launch Center (Centro de Lançamento de Alcântara, CLA), the main launch site of the Brazilian Space Program. However, their occurrence could be a risk for activities during launch missions. In this work, the observational features of wet days (daily precipitation total ≥ 1 mm/day) in the dry quarter of the CLA region were studied. Daily precipitation totals over the course of 37 years (1979-2016, except 2006), outgoing longwave radiation (OLR) data and ERA-Interim reanalysis data were used. On average, in the dry quarter, there were 9 wet days, which accumulated 32 mm. The number and quarterly precipitation total of wet days showed pronounced interannual variability. This variability was negatively and significantly correlated with the interhemispheric sea surface temperature anomalies gradient in the Atlantic Ocean and the wind speed at 925 hPa over the CLA region. Based on a theoretical distribution (log-normal), the probability of occurrence of heavy precipitation days (daily total ≥ 10 mm/day) was only 0.5%. For days with heavy precipitation and deep convection (OLR ≤ 230 W·m-2), over a large area along the northeastern coast of South America including the CLA region, negative OLR differences (from the mean) and the strengthening of favorable conditions for deep convection were found. The large-scale organization of the convective activity and atmospheric features for higher precipitation events obtained in this work could be helpful for nowcasting and short-range weather forecasting during launch missions at the CLA.

scholarly journals Investigating the Factors That Contribute to African Easterly Wave Intensity Forecast Uncertainty in the ECMWF Ensemble Prediction System

2019 ◽  
Vol 147 (5) ◽  
pp. 1679-1698
Author(s):  
Travis J. Elless ◽  
Ryan D. Torn
Keyword(s):  
Large Scale ◽  
Ensemble Prediction ◽  
Prediction System ◽  
African Easterly Waves ◽  
Ensemble Prediction System ◽  
Easterly Waves ◽  
Convectively Coupled Equatorial Waves ◽  
Easterly Wave ◽  
Equatorial Wave ◽  
Diabatic Processes

Abstract Although there have been numerous studies documenting the processes/environments that lead to the intensification of African easterly waves (AEWs), only a few of these studies investigated the effect of those processes or the environment on the predictability of AEWs. Here, the large-scale modulation of AEW intensity predictability is evaluated using the 51-member ECMWF ensemble prediction system (EPS) during an active AEW period (July–September 2011–13). Forecasts are stratified based on the 72-h AEW intensity standard deviation (SD) to evaluate hypotheses for how different processes contribute to large forecast SD. While large and small SD forecasts are associated with similar baroclinic and barotropic energy conversions, forecasts with large SD are characterized by higher relative humidity values downstream of the AEW trough. These areas of higher humidity are also associated with higher precipitation and precipitation SD, suggesting that uncertainty associated with diabatic processes could be linked with large AEW intensity SD. Although water vapor is a strong function of longitude and phase of convectively coupled equatorial waves, the cases with large and small SD are characterized by similar longitude and wave phase, suggesting that AEWs occurring in certain locations or convectively coupled equatorial wave phases are not more or less predictable.

scholarly journals Observations of Seven African Easterly Waves in the East Atlantic during 2006

2010 ◽  
Vol 67 (1) ◽  
pp. 26-43 ◽  
Author(s):  
Jonathan Zawislak ◽  
Edward J. Zipser
Keyword(s):  
Large Scale ◽  
High Amplitude ◽  
African Easterly Waves ◽  
Easterly Waves ◽  
Wave Trough ◽  
Wind Structure ◽  
Easterly Wave ◽  
Global Data Assimilation System ◽  
Low Amplitude ◽  
The Relationship

Abstract The African Monsoon Multidisciplinary Analyses (AMMA) experiment and its downstream NASA extension, NAMMA, provide an unprecedented detailed look at the vertical structure of consecutive African easterly waves. During August and September 2006, seven easterly waves passed through the NAMMA domain: two waves developed into Tropical Cyclones Debby and Helene, two waves did not develop, and three waves were questionable in their role in the development of Ernesto, Florence, and Gordon. NCEP Global Data Assimilation System (GDAS) analyses are used to describe the track of both the vorticity maxima and midlevel wave trough associated with each of the seven easterly waves. Dropsonde data from NAMMA research flights are used to describe the observed wind structure and as a tool to evaluate the accuracy of the GDAS to resolve the structure of the wave. Finally, satellite data are used to identify the relationship between convection and the organization of the wind structure. Results support a necessary distinction between the large-scale easterly wave trough and smaller-scale vorticity centers within the wave. An important wave-to-wave variability is observed: for NAMMA waves, those waves that have a characteristically high-amplitude wave trough and well-defined low-level circulations (well organized) may contain less rainfall, do not necessarily develop, and are well resolved in the analysis, whereas low-amplitude (weakly organized) NAMMA waves may have stronger vorticity centers and large persistent raining areas and may be more likely to develop, but are not well resolved in the analysis.

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