scholarly journals A Recurrence Analysis of Multiple African Easterly Waves during Summer 2006

2020 ◽  
Author(s):  
Tiffany Reyes ◽  
Bo-Wen Shen
Keyword(s):  
Large Scale ◽  
Mesoscale Model ◽  
Recurrence Plot ◽  
Temporal Variations ◽  
Local Analysis ◽  
Lead Times ◽  
African Easterly Waves ◽  
Easterly Waves ◽  
Weather Forecasts

Accurate detection of large-scale atmospheric tropical waves, such as African easterly waves (AEWs), may help extend lead times for predicting tropical cyclone (TC) genesis. Since observed AEWs have comparable but slightly different periods showing spatial and temporal variations, local analysis of frequencies and amplitudes of AEWs is crucial for revealing the role of AEWs in the modulation of TC genesis. To achieve this goal, we investigate the recurrence plot (RP) method. A recurrence is defined when the trajectory of a state returns to the neighborhood of a previously visited state. To verify implementation of the RP method in Python and its capability for revealing a transition between different types of solutions, we apply the RP to analyze several idealized solutions, including periodic, quasiperiodic, chaotic and limit cycle solutions, and various types of solutions within the three- and five-dimensional Lorenz models. We then extend the RP analysis to two datasets from the European Centre for Medium-Range Weather Forecasts global reanalysis and global mesoscale model data in order to reveal the recurrence of multiple AEWs during summer 2006. Our results indicate that the RP analysis effectively displays the major features of time-varying oscillations and the growing or decaying amplitudes of multiple AEWs.

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

scholarly journals An Evaluation of the Parallel Ensemble Empirical Mode Decomposition Method in Revealing the Role of Downscaling Processes Associated with African Easterly Waves in Tropical Cyclone Genesis

2016 ◽  
Vol 33 (8) ◽  
pp. 1611-1628 ◽  
Author(s):  
Yuling Wu ◽  
Bo-Wen Shen
Keyword(s):  
Tropical Cyclone ◽  
Empirical Mode Decomposition ◽  
Ensemble Empirical Mode Decomposition ◽  
Reanalysis Data ◽  
Tropical Cyclone Genesis ◽  
African Easterly Waves ◽  
Horizontal Shear ◽  
Easterly Waves ◽  
Mode Decomposition

AbstractIn this study the parallel ensemble empirical mode decomposition (PEEMD) is applied for an analysis of 10-yr (2004–13) ERA-Interim global reanalysis data in order to explore the role of downscaling processes associated with African easterly waves (AEWs) in tropical cyclone (TC) genesis. The focus of the study was aimed at understanding the downscaling process in multiscale flows during storm intensification. To represent the various length scales of atmospheric systems, intrinsic mode functions (IMFs) were extracted from the reanalysis data using the PEEMD. It was found that the nonoscillatory trend mode can be used to represent large-scale environmental flow and that the third oscillatory mode (IMF3) can be used to represent AEW/TC scale systems. The results 1) identified 42 developing cases from 272 AEWs, where 25 of them eventually developed into hurricanes; 2) indicated that the maximum for horizontal shear largely occurs over the ocean for the IMF3 and over land near the coast for the trend mode for developing cases, suggesting shear transfer between the trend mode and the IMF3; 3) displayed opposite wind shear tendencies for the trend mode and the IMF3 during storm intensification, signifying that the downscaling process was active in 13 hurricane cases along their tracks; and 4) showed that among the 42 developing cases, only 13 of the 25 hurricanes were found to have significant downscaling transfer features, so other processes such as upscaling processes may play an important role in the other developing cases, especially for the remaining 12 hurricane cases. In a future study, the authors intend to investigate the upscaling process between the convection scale and AEWs/TCs, which requires data at a finer grid resolution.

Four Years of Tropical ERA-40 Vorticity Maxima Tracks. Part I: Climatology and Vertical Vorticity Structure

2008 ◽  
Vol 136 (11) ◽  
pp. 4301-4319 ◽  
Author(s):  
Brandon Kerns ◽  
Kantave Greene ◽  
Edward Zipser
Keyword(s):  
Large Scale ◽  
Easterly Waves ◽  
Weather Forecasts ◽  
East Pacific ◽  
Cloud Clusters ◽  
Geographical Separation ◽  
Medium Range ◽  
Strong Gradient ◽  
Upper Level ◽  
Vorticity Structure

Abstract Using the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40), vorticity maxima (VM) have been manually tracked and classified as developing and nondeveloping. The VM are identified on Hovmöller plots for June–October 1998–2001, within 0°–35°N, 140°–10°W. Over 600 low-level and midlevel VM are tracked. The ERA-40 VM track climatology compares favorably with previous knowledge about easterly waves. Some new results have also been found. The VM are not equivalent to easterly waves, so it is important to distinguish between the large-scale wave and the embedded VM. Unlike waves, individual VM leaving Africa generally do not survive to cross the entire Atlantic. Unlike waves, which can cross Central America, most individual east Pacific VM originate in the east Pacific. Genesis productivity is defined as the fraction of nontropical cyclone VM that eventually develop. It reaches 50% in the eastern North Pacific (EPAC) and 30% in the Atlantic, where there is geographical separation between the locations of maximum nondeveloping and pregenesis track density. There is a strong gradient in daily genesis potential (DGP) near 10°N, associated with weaker upper-level anticyclonic vorticity equatorward of 10°N. The maximum genesis productivity is obtained north of 10°N, where the upper-anticyclonic vorticity and DGP are higher. Finally, there is no obvious distinction in VM strength between developing VM prior to genesis and nondeveloping VM. A major factor is the minimum vorticity threshold for VM as opposed to cloud clusters.

scholarly journals Role of Convective Entrainment in Spatial Distributions of and Temporal Variations in Precipitation over Tropical Oceans

2014 ◽  
Vol 27 (23) ◽  
pp. 8707-8723 ◽  
Author(s):  
Nagio Hirota ◽  
Yukari N. Takayabu ◽  
Masahiro Watanabe ◽  
Masahide Kimoto ◽  
Minoru Chikira
Keyword(s):  
Large Scale ◽  
Lower Troposphere ◽  
Temporal Variations ◽  
Spatial And Temporal Variations ◽  
Spatial Distributions ◽  
Atmospheric Models ◽  
Tropical Oceans ◽  
Appropriate Treatment ◽  
Precipitation Events

Abstract The authors demonstrate that an appropriate treatment of convective entrainment is essential for determining spatial distributions of and temporal variations in precipitation. Four numerical experiments are performed using atmospheric models with different entrainment characteristics: a control experiment (Ctl), a no-entrainment experiment (NoEnt), an original Arakawa–Schubert experiment (AS), and an AS experiment with a simple empirical suppression of convection depending on cloud-layer humidity (ASRH). The fractional entrainment rates of AS and ASRH are constant for each cloud type and are very small in the lower troposphere compared with those in the Ctl, in which half of the buoyancy-generated energy is consumed by entrainment. Spatial and temporal variations in the observed precipitation are satisfactorily reproduced in the Ctl, but their amplitudes are underestimated with a so-called double intertropical convergence zone bias in the NoEnt and AS. The spatial variation is larger in the Ctl because convection is more active over humid ascending regions and more suppressed over dry subsidence regions. Feedback processes involving convection, the large-scale circulation, free tropospheric moistening by congestus, and radiation enhance the variations. The temporal evolution of precipitation events is also more realistic in the Ctl, because congestus moistens the midtroposphere, and large precipitation events occur once sufficient moisture is available. The large entrainment in the lower troposphere, increasing free tropospheric moistening by congestus and enhancing the coupling of convection to free tropospheric humidity, is suggested to be important for the realistic spatial and temporal variations.

Probabilistic Evaluation of the Dynamics and Predictability of the Mesoscale Convective Vortex of 10–13 June 2003

2007 ◽  
Vol 135 (4) ◽  
pp. 1544-1563 ◽  
Author(s):  
Daniel P. Hawblitzel ◽  
Fuqing Zhang ◽  
Zhiyong Meng ◽  
Christopher A. Davis
Keyword(s):  
Large Scale ◽  
Mesoscale Model ◽  
Critical Role ◽  
Probabilistic Evaluation ◽  
Mesoscale Convective ◽  
Upper Level ◽  
Mesoscale Convective Vortex ◽  
Horizontal Grid ◽  
Development And Evolution

Abstract This study examines the dynamics and predictability of the mesoscale convective vortex (MCV) of 10–13 June 2003 through ensemble forecasting. The MCV of interest developed from a preexisting upper-level disturbance over the southwest United States on 10 June and matured as it traveled northeastward. This event is of particular interest given the anomalously strong and long-lived nature of the circulation. An ensemble of 20 forecasts using a 2-way nested mesoscale model with horizontal grid increments of 30 and 10 km are employed to probabilistically evaluate the dynamics and predictability of the MCV. Ensemble mean and spread as well as correlations between different forecast variables at different forecast times are examined. It is shown that small-amplitude large-scale balanced initial perturbations may result in very large ensemble spread, with individual solutions ranging from a very strong MCV to no MCV at all. Despite similar synoptic-scale conditions, the ensemble MCV forecasts vary greatly depending on intensity and coverage of simulated convection, illustrating the critical role of convection in the development and evolution of this MCV. Correlation analyses reveal the importance of a preexisting disturbance to the eventual development of the MCV. It is also found that convection near the center of the MCV the day after its formation may be an important factor in determining the eventual growth of a surface vortex and that a stronger midlevel vortex is more conducive to convection, especially on the downshear side, consistent with the findings of previous MCV studies.

NASA’s Contributions to the 2021 Aeolus Field Campaign: CPEX-AW

2021 ◽  
Author(s):  
Gail Skofronick-Jackson ◽  
Aaron Piña ◽  
Shuyi Chen
Keyword(s):  
High Altitude ◽  
Integrated Circuit ◽  
Satellite System ◽  
African Easterly Waves ◽  
Field Campaign ◽  
Easterly Waves ◽  
Weather Forecasts ◽  
Wind Lidar ◽  
Simulated Field ◽  
The Tropics

<p>In 2020, a joint NASA-ESA campaign focusing on the tropics was planned to take place in Cabo Verde. This campaign, now delayed to 2021, was designed to engage the broader scientific atmospheric dynamics community and to assist in calibrating and validating the recently launched ESA Aeolus wind lidar satellite system. This campaign is an opportunity to join the U.S. and European airborne wind lidar system teams addressing the Aeolus calibration and validation. Nominally, the NASA contribution is a follow-on to the Convective Processes Experiment (CPEX) field campaign which took place in 2017 (https://cpex.jpl.nasa.gov/). The 2021 field campaign will add an aerosol (A) and winds (W) component—CPEX-AW—and will provide opportunities to study the dynamics and microphysics related to the Saharan air layer, African easterly waves and jets, the marine atmospheric boundary layer, and convection that not only advance our understanding of tropical dynamics but also improve weather forecasts. The NASA component of the field campaign plans to begin intensive operations in early July 2021 and will continue until mid-August. Approximately 150 flight hours are planned on NASA’s DC-8 aircraft. Planned instruments are the Doppler Aerosol WiNd Lidar (DAWN), the High Altitude Lidar Observatory (HALO), the APR-3 radar (Ku, Ka, and W bands), the High Altitude Monolithic Microwave integrated Circuit (MMIC) Sounding Radiometer (HAMSR), and dropsondes. During Summer 2020, NASA’s team hosted a dry run of a simulated field campaign which included virtual flights. In this talk, we will discuss the plans for NASAs contributions to the 2021 Aeolus Field Campaign and present preliminary findings from using Aeolus data and CPEX-AW dry-run virtual flights.</p>

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.

scholarly journals Thunderstorms Do Not Get Butterflies

2016 ◽  
Vol 97 (2) ◽  
pp. 237-243 ◽  
Author(s):  
Dale R. Durran ◽  
Jonathan A. Weyn
Keyword(s):  
Large Scale ◽  
Squall Line ◽  
Small Scale ◽  
Lead Times ◽  
Initial State ◽  
Weather Forecasts ◽  
Kinetic Energy Spectrum ◽  
Initial Errors ◽  
Squall Lines ◽  
Homogeneous Environment

Abstract One important limitation on the accuracy of weather forecasts is imposed by unavoidable errors in the specification of the atmosphere’s initial state. Much theoretical concern has been focused on the limits to predictability imposed by small-scale errors, potentially even those on the scale of a butterfly. Very modest errors at much larger scales may nevertheless pose a more important practical limitation. We demonstrate the importance of large-scale uncertainty by analyzing ensembles of idealized squall-line simulations. Our results imply that minimizing initial errors on scales around 100 km is more likely to extend the accuracy of forecasts at lead times longer than 3–4 h than efforts to minimize initial errors on much smaller scales. These simulations also demonstrate that squall lines, triggered in a horizontally homogeneous environment with no initial background circulations, can generate a background mesoscale kinetic energy spectrum roughly similar to that observed in the atmosphere.

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.

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