Sensitivity of African easterly waves to boundary layer conditions

Lenouo, André; Kamga, F. Mkankam

doi:10.5194/angeo-26-1355-2008

Cited by 7 publications

(4 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This jet corresponds to the one seen in the atmosphere during summer at an altitude of around 3000 m in the Northern African troposphere. The principal phase velocity is found to be 7.0 m/s [22][23][24].…”

Section: Resultsmentioning

confidence: 94%

“…The value of 1 can be found in a mosaic of satellite images for the period August 20-24, 2006, taken every six hours as shown in Figure 5. The total velocity of the wave is around 15 m/s where the classical value of AEW velocity is 10 m/s [21,22,24]; then we deduce that the additional wave (soliton) velocity is about 5 m/s. This figure presents a very distinct signal that can be tracked from an initial region of convection, developing through several stages and moving off the African coast.…”

Section: Case Of Ts Debbymentioning

confidence: 97%

See 1 more Smart Citation

Solitary Rossby Waves in the Lower Tropical Troposphere

Lenouo

Nkankam

2013

ISRN Atmospheric Sciences

View full text Add to dashboard Cite

Weakly nonlinear approximation is used to study the theoretical comportment of large-scale disturbances around the intertropical midtropospheric jet. We show here that the Korteweg de Vries (KdV) theory is appropriated to describe the structure of the streamlines around the African easterly jet (AEJ) region. The introduction of the additional velocity of the soliton C 1 permits to search the stage where the configuration of the wave structures is going to emerge out of specified initial conditions and this is the direct and inverse cascade method. It was also shown that the configurations of disturbances can be influenced by this parameter so that we can look if the disturbances are in the control or not of their dispersive effects. This permits to explain the evolution of initial conditions of the Tropical Storm (TS) Debby over West Africa from 20 to 24 August 2006.

show abstract

Section: Resultsmentioning

confidence: 94%

Section: Case Of Ts Debbymentioning

confidence: 97%

Solitary Rossby Waves in the Lower Tropical Troposphere

Lenouo

Nkankam

2013

ISRN Atmospheric Sciences

View full text Add to dashboard Cite

show abstract

“…During MAM and SON (Figure b,d), GPCP illustrates the band of maximum precipitation between 5°S and 6°N, while during JJA (Figure c), the tropical rain‐belt moves to its northernmost position and reaches its peak which is lying around 9°N. In fact, this tropical rain‐belt is produced by a large ascension core located between the African Easterly Jet (AEJ) and the Tropical Easterly Jet, which are important features controlling the African monsoon variability (Lenouo and Kamga, ; Nicholson, ; Sylla et al ., ).…”

Section: Resultsmentioning

confidence: 97%

An evaluation of COSMO‐CLM regional climate model in simulating precipitation over Central Africa

Fotso‐Nguemo

Diallo

Pokam

et al. 2019

Intl Journal of Climatology

View full text Add to dashboard Cite

In this study, an analysis of present day climate simulation (1998–2008) is presented for the Central African (CA) region with the COnsortium for Small‐scale MOdelling in CLimate Mode (CCLM) regional climate model, forced by the ERA‐Interim (ERAINT) reanalysis data. The ability of the CCLM to simulate the observed precipitation with particular focus on the mean spatial pattern, low‐level circulation, seasonal cycles, and daily characteristics is evaluated. Likewise, the added value of the regional model CCLM compared to the driving ERAINT reanalysis is also investigated. It is shown that ERAINT and CCLM exhibit quite different sign of bias, which is an indication of the importance of internal variability and fine scale processes representation for the simulation of surface climate. Despite the CCLM is constantly dry over southern CA, the model succeeds to reproduce reasonably the mean spatial patterns of precipitation and low‐level circulation features, along with the associated seasonal cycles over the whole CA and majority of the five selected analysis sub‐regions. Results also show that daily precipitation indices are well represented, although the better performance greatly depends on the considered seasons. Nevertheless, CCLM substantially outperforms the ERAINT daily precipitation characteristics, thus highlighting the added value of the downscaling exercise over the region. The analysis of daily precipitation indices also reveals that the dry character of the model could probably be connected to the underestimation of the simulated less intense events, which in turn result to an overestimation of the simulated dry spell duration.

show abstract

“…The resulting biases may involve errors in the initial and boundary conditions due to sparse observational data available for the region, as well as issues resulting from physical parameterizations in Africa (FLAOUNAS et al 2010;POHL et al 2011;CRETAT et al 2012). Rainfall biases in particular may be related to model deficiencies in simulating African easterly and equatorial waves, which have been shown to favor strong convective events over West and Central Africa (JANICOT 1992;LENOUO and KAMGA 2008).…”

Section: Forecast Verification and Analysis Incrementmentioning

confidence: 99%

Added-Value of 3DVAR Data Assimilation in the Simulation of Heavy Rainfall Events Over West and Central Africa

Igri

Tanessong

Vondou

et al. 2015

Pure Appl. Geophys.

View full text Add to dashboard Cite

This study aimed to evaluate the ability of a numerical weather prediction (NWP) model to capture the spatial distribution and magnitude of rainfall during three recent intense events (15-17 June 2011, and 23-25 August and 04-06 September 2012) observed over West and Central Africa, as well as the associated atmospheric and near-surface conditions. For each event, two numerical experiments were performed using the regional Weather Research and Forecasting (WRF) Model without (CNTL) and with (DA) data assimilation. Simulations were initialized using Global Forecast System data. The analyses were updated with the three-dimensional variational (3DVAR) technique using PrepBUFR and radiance observational data in a time window of ±3 h. The potential added value of data assimilation was addressed by comparing meteorological variables such as relative humidity, zonal and meridional wind components, 2 m temperature, and rainfall with the European Centre for Medium-Range Weather Forecasts reanalysis and the Tropical Rainfall Measuring Mission satellite-derived rainfall product datasets. WRF accurately simulated the spatiotemporal propagation and the zonally extended structure of rainfall as well as of relative humidity, 2 m temperature, and horizontal wind components. DA exhibited different biases, root mean square error, and spatial correlation, leading to mixed results in terms of outperforming CNTL. Results indicated that there was an increment in control variables, implying an added value from 3DVAR to the initial and boundary conditions. Rainfall forecasts were improved by 15-25 %. Uncertainties in the simulation of intense events in the study domain were noted, but improvement resulting from DA was limited due to lack of assimilated data for the region.

show abstract

Sensitivity of African easterly waves to boundary layer conditions

Cited by 7 publications

References 26 publications

Solitary Rossby Waves in the Lower Tropical Troposphere

Solitary Rossby Waves in the Lower Tropical Troposphere

An evaluation of COSMO‐CLM regional climate model in simulating precipitation over Central Africa

Added-Value of 3DVAR Data Assimilation in the Simulation of Heavy Rainfall Events Over West and Central Africa

Contact Info

Product

Resources

About