Future change in precipitation seasonality over the Horn of Africa in high-resolution simulation

2020 ◽  
Author(s):  
Pratik Kad ◽  
Kyung-Ja Ha
Keyword(s):  
High Resolution ◽  
East Africa ◽  
Seasonal Cycle ◽  
Model Simulation ◽  
Horn Of Africa ◽  
Future Change ◽  
Short Rain ◽  
Rain Season ◽  
Future Global Warming ◽  
Precipitation Seasonality

<p>Extreme weather creating a widespread humanitarian crisis over East Africa in recent decades. The seasonal cycle of precipitation over the Horn of Africa (HOA) shows bimodality with long rain and short rain. Most of the models fail to capture biannual rainfall seasonal cycles, due to circulation response to unrealistically dominate the annual mean. The Community Earth System Model (CESM) high-resolution model simulation has been employed to study the sensitivity. Precipitation distribution over HOA shows regional variations where most of the region show the bimodal distribution and the intrinsically complex. This bimodality is nominally associated with tropical rain belt, but topography and SST-forcing also play an important role in influencing the timing and intensity of seasonal rainfall. The results show that overall rainfall seasonality is increased, with intensification over high elevation. Precise representation of rainfall seasonal cycle over HOA adds confidence for future projected changes in seasonality. An important question is whether and how the seasonal cycle over HOA responds to anthropogenic forcing. We show that the future change in precipitation seasonal cycle and accumulation over HOA can be explained by the surface ocean process which module SSTs along the coastline of Somalia. The moisture convergence over low elevation land is basically regulated through the north-south SST gradient. In conclusion, future global warming leads to the intensified seasonal cycle of precipitation with a projected increase in the short rain season over east Africa. Further analysis demonstrates how topography modulates the seasonality of HOA.</p>

Introduction

2018 ◽  
Author(s):  
Marina Sharpe
Keyword(s):  
West Africa ◽  
Great Lakes ◽  
East Africa ◽  
North Africa ◽  
Southern Africa ◽  
Theoretical Approach ◽  
Central Africa ◽  
Horn Of Africa ◽  
Refugee Protection

This introductory chapter begins by presenting the book’s structure in section A. Section B then delineates the book’s contours, outlining four aspects of refugee protection in Africa that are not addressed. Section C provides context, with a contemporary overview of the state of refugee protection in Africa. It also looks at the major aspects of the refugee situations in each of Africa’s principal geographic sub-regions: East Africa (including the Horn of Africa), Central Africa and the Great Lakes, West Africa, Southern Africa, and North Africa. Section D then concludes with an outline of the theoretical approach to regime relationships employed throughout the book.

Examining Terrain Effects on an Upstate New York Tornado Event Utilizing a High-Resolution Model Simulation

2021 ◽  
Author(s):  
Luke J. LeBel ◽  
Brian H. Tang ◽  
Ross A. Lazear
Keyword(s):  
New York ◽  
High Resolution ◽  
Wind Shear ◽  
Model Simulation ◽  
Wrf Model ◽  
Severe Weather ◽  
Streamwise Vorticity ◽  
Low Level ◽  
Severe Convection ◽  
The Impact

AbstractThe complex terrain at the intersection of the Mohawk and Hudson valleys of New York has an impact on the development and evolution of severe convection in the region. Specifically, previous research has concluded that terrain-channeled flow in the Mohawk and Hudson valleys likely contributes to increased low-level wind shear and instability in the valleys during severe weather events such as the historic 31 May 1998 event that produced a strong (F3) tornado in Mechanicville, New York.The goal of this study is to further examine the impact of terrain channeling on severe convection by analyzing a high-resolution WRF model simulation of the 31 May 1998 event. Results from the simulation suggest that terrain-channeled flow resulted in the localized formation of an enhanced low-level moisture gradient, resembling a dryline, at the intersection of the Mohawk and Hudson valleys. East of this boundary, the environment was characterized by stronger low-level wind shear and greater low-level moisture and instability, increasing tornadogenesis potential. A simulated supercell intensified after crossing the boundary, as the larger instability and streamwise vorticity of the low-level inflow was ingested into the supercell updraft. These results suggest that terrain can have a key role in producing mesoscale inhomogeneities that impact the evolution of severe convection. Recognition of these terrain-induced boundaries may help in anticipating where the risk of severe weather may be locally enhanced.

scholarly journals Contrasting seasonal changes in total and intense precipitation in the European Alps from 1903 to 2010

2020 ◽  
Author(s):  
Martin Ménégoz ◽  
Evgenia Valla ◽  
Nicolas C. Jourdain ◽  
Juliette Blanchet ◽  
Julien Beaumet ◽  
...  
Keyword(s):  
High Resolution ◽  
Spatial Variability ◽  
Seasonal Changes ◽  
Seasonal Cycle ◽  
Climate Model ◽  
Regional Climate ◽  
Vertical Gradient ◽  
P Value ◽  
European Alps ◽  
High Elevations

Abstract. Changes of precipitation over the European Alps are investigated with the regional climate model MAR applied with a 7-km resolution over the period 1903–2010 using the reanalysis ERA-20C as forcing. A comparison with several observational datasets demonstrates that the model is able to reproduce the climatology as well as both the inter-annual variability and the seasonal cycle of precipitation over the European Alps. The relatively high resolution allows to estimate precipitation at high elevations. The vertical gradient of precipitation simulated by MAR over the European Alps reaches 33 % km−1 (1.21 mm.day−1.km−1) in summer and 38 % km−1 (1.15 mm.day−1.km−1) in winter, on average over 1971–2008 and shows a large spatial variability. A significant (p-value 

scholarly journals Prolific Lightning and Thunderstorm Initiation over the Lake Victoria Basin in East Africa

2020 ◽  
Vol 148 (5) ◽  
pp. 1971-1985 ◽  
Author(s):  
Katrina S. Virts ◽  
Steven J. Goodman
Keyword(s):  
East Africa ◽  
Hot Spots ◽  
Seasonal Cycle ◽  
Lake Victoria ◽  
Intertropical Convergence Zone ◽  
Lake Victoria Basin ◽  
The Earth ◽  
Total Lightning ◽  
Average Cluster

Abstract The Lake Victoria basin of East Africa is home to over 30 million people, over 200 000 of whom are employed in fishing or transportation on the lake. Approximately 3000–5000 individuals are killed by thunderstorms yearly, primarily by outflow winds and resulting large waves. Prolific lightning activity and thunderstorm initiation in the basin are examined using continuous total lightning observations from the Earth Networks Global Lightning Network (ENGLN) for September 2014–August 2018. Seasonal shifts in the intertropical convergence zone produce semiannual lightning maxima over the lake. Diurnally, solar heating and lake and valley breezes produce daytime lightning maxima north and east of the lake, while at night the peak lightning density propagates southwestward across the lake. Cluster analysis reveals terrain-related thunderstorm initiation hot spots northeast of the lake; clusters also initiate over the lake and northern lowlands. The most prolific clusters initiate between 1100 and 1400 LT, about 1–2 h earlier than the average cluster. Most daytime thunderstorms dissipate without reaching Lake Victoria, and annually 85% of clusters producing over 1000 flashes over Lake Victoria initiate in situ. Initiation times of prolific Lake Victoria clusters exhibit a bimodal seasonal cycle: equinox-season thunderstorms initiate most frequently between 2200 and 0400 LT, while solstice-season thunderstorms initiate most frequently from 0500 to 0800 LT, more than 12 h after the afternoon convective peak over land. More extreme clusters are more likely to have formed over land and propagated over the lake, including 36 of the 100 most extreme Lake Victoria thunderstorms. These mesoscale clusters are most common during February–April and October–November.

scholarly journals Deriving stratospheric age of air spectra using chemically active trace gases

2018 ◽  
Author(s):  
Marius Hauck ◽  
Frauke Fritsch ◽  
Hella Garny ◽  
Andreas Engel
Keyword(s):  
Seasonal Cycle ◽  
Inverse Method ◽  
Model Simulation ◽  
Trace Gases ◽  
Global Scale ◽  
Point Of View ◽  
Full Description ◽  
Mixing Ratios ◽  
Tropical Tropopause ◽  
Single Entry

Abstract. Analysis of stratospheric transport from an observational point of view is frequently realized by evaluation of mean age of air values from long-lived trace gases. However, this provides more insight into general transport strength and less into its mechanism. Deriving complete transit time distributions (age spectra) is desirable, but their deduction from direct measurements is difficult and so far primarily achieved by assumptions about dynamics and spectra themselves. This paper introduces a modified version of an inverse method to infer age spectra from mixing ratios of short-lived trace gases. For a full description of transport seasonality the formulation includes an imposed seasonal cycle to gain multimodal spectra. The EMAC model simulation used for a proof of concept features an idealized dataset of 40 radioactive trace gases with different chemical lifetimes as well as 40 chemically inert pulsed trace gases to calculate pulse age spectra. Annual and seasonal mean inverse spectra are compared to pulse spectra including first and second moments as well as the ratio between them to assess the performance on these time scales. Results indicate that the modified inverse age spectra match the annual and seasonal pulse age spectra well on global scale beyond 1.5 years mean age of air. The imposed seasonal cycle emerges as a reliable tool to include transport seasonality in the age spectra. Below 1.5 years mean age of air, tropospheric influence intensifies and breaks the assumption of single entry through the tropical tropopause, leading to inaccurate spectra in particular in the northern hemisphere. The imposed seasonal cycle wrongly prescribes seasonal entry in this lower region and does not lead to a better agreement between inverse and pulse age spectra without further improvement. As the inverse method aims for future implementation on in situ observational data, possible critical factors for this purpose are delineated finally.

scholarly journals Understanding Satellite-Observed Mountain-Wave Signatures Using High-Resolution Numerical Model Data

2009 ◽  
Vol 24 (1) ◽  
pp. 76-86 ◽  
Author(s):  
W. F. Feltz ◽  
K. M. Bedka ◽  
J. A. Otkin ◽  
T. Greenwald ◽  
S. A. Ackerman
Keyword(s):  
Water Vapor ◽  
High Resolution ◽  
Weighting Function ◽  
Model Simulation ◽  
Wave Train ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Model Data ◽  
Mountain Wave ◽  
Mountain Waves

Abstract Prior work has shown that pilot reports of severe turbulence over Colorado often occur when complex interference or crossing wave patterns are present in satellite water vapor imagery downstream of the Rocky Mountains. To improve the understanding of these patterns, a high-resolution (1-km) Weather Research and Forecasting (WRF) model simulation was performed for an intense mountain-wave event that occurred on 6 March 2004. Synthetic satellite imagery was subsequently generated by passing the model-simulated data through a forward radiative transfer model. Comparison with concurrent Moderate Resolution Imaging Spectroradiometer (MODIS) water vapor imagery demonstrates that the synthetic satellite data realistically captured many of the observed mesoscale features, including a mountain-wave train extending far downstream of the Colorado Front Range, the deformation of this wave train by an approaching cold front, and the substantially warmer brightness temperatures in the lee of the major mountain ranges composing the Colorado Rockies. Inspection of the model data revealed that the mountain waves redistributed the water vapor within the lower and middle troposphere, with the maximum column-integrated water vapor content occurring one-quarter wavelength downstream of the maximum ascent within each mountain wave. Due to this phase shift, the strongest vertical motions occur halfway between the locally warm and cool brightness temperature couplets in the water vapor imagery. Interference patterns seen in the water vapor imagery appear to be associated with mesoscale variability in the ambient wind field at or near mountaintop due to flow interaction with the complex topography. It is also demonstrated that the synergistic use of multiple water vapor channels provides a more thorough depiction of the vertical extent of the mountain waves since the weighting function for each channel peaks at a different height in the atmosphere.

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