scholarly journals African easterly waves in 30-day high-resolution global simulations: A case study during the 2006 NAMMA period

2010 ◽  
Vol 37 (18) ◽  
pp. n/a-n/a ◽  
Author(s):  
Bo-Wen Shen ◽  
Wei-Kuo Tao ◽  
Man-Li C. Wu
Keyword(s):  
High Resolution ◽  
African Easterly Waves ◽  
Easterly Waves

scholarly journals Land–Atmosphere Coupling Sensitivity to GCMs Resolution: A Multimodel Assessment of Local and Remote Processes in the Sahel Hot Spot

2021 ◽  
Vol 34 (3) ◽  
pp. 967-985
Author(s):  
Omar V. Müller ◽  
Pier Luigi Vidale ◽  
Benoît Vannière ◽  
Reinhard Schiemann ◽  
Retish Senan ◽  
...  
Keyword(s):  
Soil Moisture ◽  
High Resolution ◽  
Large Scale ◽  
Hot Spot ◽  
Moisture Flux ◽  
Horizontal Wind ◽  
African Easterly Waves ◽  
Atmospheric Conditions ◽  
Easterly Waves ◽  
Duration Comparison

AbstractLand–atmosphere interactions are often interpreted as local effects, whereby the soil state drives local atmospheric conditions and feedbacks originate. However, nonlocal mechanisms can significantly modulate land–atmosphere exchanges and coupling. We make use of GCMs at different resolutions (low ~1° and high ~0.25°) to separate the two contributions to coupling: better represented local processes versus the influence of improved large-scale circulation. We use a two-legged metric, complemented by a process-based assessment of four CMIP6 GCMs. Our results show that weakening, strengthening, and relocation of coupling hot spots occur at high resolution globally. The northward expansion of the Sahel hot spot, driven by nonlocal mechanisms, is the most notable change. The African easterly jet’s horizontal wind shear is enhanced in JJA due to better resolved orography at high resolution. This effect, combined with enhanced easterly moisture flux, favors the development of African easterly waves over the Sahel. More precipitation and soil moisture recharge produce strengthening of the coupling, where evapotranspiration remains controlled by soil moisture, and weakening where evapotranspiration depends on atmospheric demand. In SON, the atmospheric influence is weaker, but soil memory helps to maintain the coupling between soil moisture and evapotranspiration and the relocation of the hot spot at high resolution. The multimodel agreement provides robust evidence that atmospheric dynamics determines the onset of land–atmosphere interactions, while the soil state modulates their duration. Comparison of precipitation, soil moisture, and evapotranspiration against satellite data reveals that the enhanced moistening at high resolution significantly reduces model biases, supporting the realism of the hot-spot relocation.

scholarly journals Late 21st Century Projected Changes in the Relationship between Precipitation, African Easterly Jet, and African Easterly Waves

Atmosphere ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 353
Author(s):  
Ibourahima Kebe ◽  
Ismaila Diallo ◽  
Mouhamadou Bamba Sylla ◽  
Fernando De Sales ◽  
Arona Diedhiou
Keyword(s):  
High Resolution ◽  
West Africa ◽  
21St Century ◽  
Regional Climate ◽  
Historical Period ◽  
African Easterly Waves ◽  
Easterly Waves ◽  
African Easterly Jet ◽  
Late 21St Century ◽  
Sahel Region

The present study utilizes three high-resolution simulations from the Regional Climate Model version 4 (RegCM4) to examine the late 21st century changes (2080–2099) in the West African Monsoon (WAM) features. A set of three Earth System Models are utilized to provide initial and lateral boundary conditions to the RegCM4 experiments. Our analysis focuses on seasonal mean changes in WAM large-scale dynamical features, along with their connections with the summer monsoon precipitation. In the historical period, the simulation ensemble means mimic reasonably well the intensity and spatial distribution of the WAM rainfall as well as the WAM circulation patterns at different scales. The future projection of the WAM climate exhibits warming over the whole West Africa leading to precipitation reduction over the Sahel region, and a slight increase over some areas of the Guinea Coast. The position of the African Easterly Jet (AEJ) is shifted southward and the African Easterly Waves (AEWs) activities are reduced, which affect in turn the WAM rainbelt characteristics in terms of position and strength. Overall the changes in simulated AEJ and AEWs contribute substantially to reduce the seasonal summer mean precipitation in West Africa by the late 21st century, with prevailing negative changes in the Savanna-Sahel region. To further explore the robustness of the relationships revealed in this paper, future studies using different high-resolution regional climate models with large ensemble are recommended.

Tracking and Verification of East Atlantic Tropical Cyclone Genesis in the NCEP Global Ensemble: Case Studies during the NASA African Monsoon Multidisciplinary Analyses

2010 ◽  
Vol 25 (5) ◽  
pp. 1397-1411 ◽  
Author(s):  
Andrew D. Snyder ◽  
Zhaoxia Pu ◽  
Yuejian Zhu
Keyword(s):  
High Resolution ◽  
Tropical Cyclone ◽  
Tropical Cyclone Genesis ◽  
African Easterly Waves ◽  
Forecast System ◽  
Ensemble Forecasts ◽  
African Monsoon ◽  
Easterly Waves ◽  
Forecast Lead Time ◽  
Cyclone Genesis

Abstract This study evaluates the performance of the NCEP global ensemble forecast system in predicting the genesis and evolution of five named tropical cyclones and two unnamed nondeveloping tropical systems during the NASA African Monsoon Multidisciplinary Analyses (NAMMA) between August and September 2006. The overall probabilities of the ensemble forecasts of tropical cyclone genesis are verified relative to a genesis time defined to be the first designation of the tropical depression from the National Hurricane Center (NHC). Additional comparisons are also made with high-resolution deterministic forecasts from the NCEP Global Forecast System (GFS). It is found that the ensemble forecasts have high probabilities of genesis for the three strong storms that formed from African easterly waves, but failed to accurately predict the pregenesis phase of two weaker storms that formed farther west in the Atlantic Ocean. The overall accuracy for the genesis forecasts is above 50% for the ensemble forecasts initialized in the pregenesis phase. The forecast uncertainty decreases with the reduction of the forecast lead time. The probability of tropical cyclone genesis reaches nearly 90% and 100% for the ensemble forecasts initialized near and in the postgenesis phase, respectively. Significant improvements in the track forecasts are found in the ensemble forecasts initialized in the postgenesis phase, possibly because of the implementation of the NCEP storm relocation scheme, which provides an accurate initial storm position for all ensemble members. Even with coarser resolution (T126L28 for the ensemble versus T384L64 for the GFS), the overall performance of the ensemble in predicting tropical cyclone genesis is compatible with the high-resolution deterministic GFS. In addition, false alarm rates for nondeveloping waves were low in both the GFS and ensemble forecasts.

scholarly journals African Easterly Waves and Cyclonic Activity over the Eastern Atlantic: Composite and Case Studies

2011 ◽  
Vol 2011 ◽  
pp. 1-14 ◽  
Author(s):  
Moctar Camara ◽  
Arona Diedhiou ◽  
Amadou Gaye
Keyword(s):  
Atlantic Ocean ◽  
Deep Convection ◽  
African Easterly Waves ◽  
Easterly Waves ◽  
Eastern Atlantic Ocean ◽  
West African Coast ◽  
Thermodynamic Conditions ◽  
Unstable Environment ◽  
Rawinsonde Data

This study aims to understand the main differences over the African continent and the Eastern Atlantic Ocean between African Easterly Waves (AEWs) associated with Atlantic cyclones (developing AEWs) and non-developing AEWs. A statistical study showed that most of the named cyclones generated near the West African coast have a long lifecycle and all are associated with intense AEWs. Using NCEP/NCAR reanalyses, a composite study of the characteristics of developing AEWs is carried out and compared to those of non-developing AEWs. Developing AEWs exhibit the greatest baroclinic and barotropic conversions which are known to be the main processes involved in AEWs growth suggesting that these AEWs are stronger than the non-developing ones. Moreover, the developing AEWs are characterized by the existence of a relatively more unstable environment over West Africa and the Atlantic Ocean. A case study using rawinsonde data showed that the developing AEW is associated with dynamic and thermodynamic conditions conducive for deep convection and subsequent cyclogenesis compared to the non-developing AEW case.

scholarly journals e-Navigating in highly-constrained waters: a case study of the Vistula Lagoon

2021 ◽  
pp. 1-10
Author(s):  
Adam Weintrit ◽  
Jacek Pietraszkiewicz ◽  
Wiesław Piotrzkowski ◽  
Wojciech Tycholiz
Keyword(s):  
High Resolution ◽  
Global Solution ◽  
Transition Process ◽  
Practical Implementation ◽  
Vistula Lagoon ◽  
Digital Era ◽  
High Resolution Bathymetry ◽  
Marine Navigation ◽  
The Vistula Lagoon

Abstract In recent years the transition of marine navigation to the digital era has been gaining momentum. Implementation of e-Navigation solutions varies from country to country in terms of their priorities, goals, levels and effects. Maritime authorities in Poland have been setting the pace in this transition process, not only in Poland but also in general as a global solution. The most recent example is the planned deployment of a variety of e-Navigation tools in the Vistula Lagoon: from GNSS-RTK Ground-Based Augmentation System, to virtual and synthetic aids to navigation, high-resolution bathymetry and advanced navigational software for piloting. The major objectives of this paper are, first, to summarise recent dynamics in the e-Navigation field, and second, to present a practical implementation of the e-Navigation concept in the Vistula Lagoon area.

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