DSpace Angular :: Browsing by Author "Amekudzi, L. K."

Browsing by Author "Amekudzi, L. K."

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Comparison of precipitable water over Ghana using GPS signals and reanalysis products
(J. Geod. Sci., 2015-11) Acheampong, A. A.; Fosu, C.; Amekudzi, L. K.; Kaas, E.
Signals from Global Navigational Satellite Systems (GNSS) when integrated with surface meteorological parameters can be used to sense atmospheric water vapour. Using gLAB software and employing precise point positioning techniques, zenith troposphere delays (ZTD) for a GPS base station at KNUST, Kumasi have been computed and used to retrieve Precipitable Water (PW). The PW values obtained were compared with products from ERA-Interim and NCEP reanalysis data. The correlation coefcients, r, determined from these comparisons were 0.839 and 0.729 for ERA-interim and NCEP respectively. This study has demonstrated that water vapour can be retrieved with high precision from GNSS signal. Furthermore, a location map have been produced to serve as a guide in adopting and installing GNSS base stations in Ghana to achieve a country wide coverage of GNSS based water vapour monitoring
Current retrieval and inter-comparisons results of Sciamachy Nighttime Nox
(Institute of Environmental Physics and Remote sensing, 2014) Amekudzi, L. K.; Bramstedt, K.; Bracher, A.; Rozanov, A.; Bovensmann, H.; Burrows, J. P.
Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) performs lunar occultation measurements over the high southern latitude (50o S–90o S). Using the global spectra fitting method by the differential optical depth approach and the optimal estimation method, vertical profiles of nighttime NOx (NO2 and NO3) are retrieved. The quality of the retrieved NOx products are verified by comparing SCIAMACHY nighttime NO2 result with other satellite instruments (HALOE and SAGE II) and NO3 results with a simple chemical model outputs. Very promising results are obtained. The relative mean differences (rmd) of SCIAMACHY-HALOE comparisons are within -16 % to +3 % and the standard deviations (rms) within 4–16 % between 25–38 km. The rmd and rms for SCIAMACHYSAGE II comparisons are within -9 % to +7 % and 10– 17 % between 22–39 km. The retrieved NO3 are in very good agreement with the model calculations between 16 to 38 km within accuracy of 25 %.
Development of high resolution rainfall climatology for Ghana
(Meteorology & Climate Science, 2014) Aryee, J.; Amekudzi, L. K.
Various sectors of the country's economy (health, energy, agriculture and the like) depend on climate, and as such availability of quality climate data becomes essential for climate impact studies in these sectors. Rainfall climate database for Ghana has been developed using Gmet station data spanning a 33-year period (1980 – 2012). Seasonal rainfall for the four agroecological zones have been derived based on 0.25o x 0.25o grids covering the entire country. This allowed a clear evidence of the Inter-Tropical Discontinuity (ITD) migration from the South of the country to the North and back. This study provides a firsthand data for climate impact study, in the aforementioned sectors, across the country.
Development of high spatial resolution rainfall data for Ghana
(International Journal of Climatology, 2018-08-25) Aryee, J. N. A.; Amekudzi, L. K.; Quansah, E.; Klutse, N. A. B.; Atiah, W. A.
Various sectors of the country’s economy – agriculture, health, energy, among others – largely depend on climate information, hence availability of quality climate data is very essential for climate-impact studies in these sectors. In this paper, a monthly rainfall database (GMet v1.0) has been developed at a 0.5∘ × 0.5∘ spatial resolution, from 113 Ghana Meteorological Agency (GMet) gauge network distributed across the four agro-ecological zones of Ghana, and spanning a 23-year period (1990–2012). The datasets were frst homogenized with quantile-matching adjustments and thereafter, gridded at a spatial resolution of 0.5∘ × 0.5∘ using Minimum Surface Curvature with tensioning parameter, allowing for comprehensive spatial felds assessment on the developed dataset. Afterwards, point-pixel validation was performed using GMet v1.0 against gauge data from stations that were earlier excluded due to large datagaps. This proved the reliability of GMet v1.0, with high and statistically signifcant correlations at 99% confdence level, and relatively low biases and rmse. Furthermore, GMet v1.0 was compared with GPCC and TRMM rainfall estimates, with both products found to adequately mimick GMet v1.0, with high correlations which are signifcant at 99% confdence level, low biases and rmse. In addition, the ratio of 90th – percentile provided fairly similar capture of extremes by both TRMM and GPCC, in relation to GMet v1.0. Finally, based on annual rainfall totals and monthly variability, k-means cluster analysis was performed on GMet v1.0, which delineated the country into four distinct climatic zones. The developed rainfall data, when offcially released, will be a useful product for climate impact and further rainfall validation studies in Ghana.
The dynamics–aerosol– chemistry–cloud interactions in West Africa Field Campaign
(American Meteorological Society, 2018-01) Flamant, C.; Knippertz, P.; Amekudzi, L. K.; et-al
First performance assessment of blends of jatropha, palm oil and soya bean biodiesel with kerosene as fuel for domestic purposes in rural-Ghana
(International Journal of Energy and Environment (IJEE), 2011) Quansah, E.; Preko, K.; Amekudzi, L. K.
Performance assessments of jatropha, palm oil and soya bean based biodiesel were carried out to investigate their potential use as conventional substitute for kerosene for domestic purposes in ruralGhana. The assessments were done by comparing some of the combustion characteristics of blends of the biodiesel with kerosene. The blends were categorised as B100 (100% biodiesel), B80 (80% biodiesel and 20% kerosene), B60 (60% biodiesel and 40% kerosene), B40 (40% biodiesel and 60% kerosene), B20 (20% biodiesel and 80% kerosene) and B0 (pure kerosene). The results showed that the calorific values of the B100s were less than that of the B0 and decreasing in the order of jatropha, soya bean and palm oil. The wick wastage results for both the B100s and B0, revealed higher rates in the WTL than the BB even though the BB recorded low fuel consumption rates than the WTL for both B100s and B0. Similarly, the luminous intensity test with the B100s showed low values in WTL than the BB in a decreasing order of jatropha, soya bean and palm oil. However, B0 recorded higher luminous intensity values that were quite comparable in both WTL and BB.
The Influence of Temperature and Relative Humidity on Indoor Ozone Concentrations during the Harmattan
(Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS), 2012) Quansah, E.; Amekudzi, L. K.; Preko, K.
A study to understand the influence of temperature and relative humidity on indoor ozone levels during the Harmattan season over Kotei, a suburb of Kumasi in Ghana has been carried out. The hourly-maximum and average ozone concentrations were measured using the A-22 Eco sensor. A strong diurnal variation of ozone levels within 0.004 and 0.229 ppm for the measurement period was observed. Ozone levels were found to be slightly above the World Health Organisation (WHO) recommended ambient air quality ozone concentration. A strong correlation coefficient of 0.75 and -0.63 for ozone was found with temperature and relative humidity respectively. This indicates that in addition to particulate matter, high ozone levels could contribute to respiratory health problems during the Harmattan season.
Precipitation variability and trends in Ghana: An intercomparison of observational and reanalysis products
(Climatic Change, 2014) Manzanas, R.; Amekudzi, L. K.; Preko, K.; Herrera, S.; Gutierrez, J. M.
Inter-annual variability and trends of annual/seasonal precipitation totals in Ghana are analyzed considering different gridded observational (gauge- and/or satellitebased) and reanalysis products. A quality-controlled dataset formed by fourteen gauges from the Ghana Meteorological Agency (GMet) is used as reference for the period 1961–2010. Firstly, a good agreement is found between GMet and all the observational products in terms of variability, with better results for the gauge-based products— correlations in the range of 0.7–1.0 and nearly null biases—than for the satellite-gauge merged and satellite-derived products. In contrast, reanalyses exhibit a very poor performance, with correlations below 0.4 and large biases in most of the cases. Secondly, a Mann-Kendall trend analysis is carried out. In most cases, GMet data reveal the existence of predominant decreasing (increasing) trends for the first (second) half of the period of study, 1961–1985 (1986–2010). Again, observational products are shown to reproduce well the observed trends—with worst results for purely satellite-derived data—whereas reanalyses lead in general to unrealistic stronger than observed trends, with contradictory results (opposite signs for different reanalyses) in some cases. Similar inconsistencies are also found when analyzing trends of extreme precipitation indicators. Therefore, this study provides a warning concerning the use of reanalysis data as pseudo-observations in Ghana.
Retrieval of stratospheric NO3 vertical profiles from SCIAMACHY lunar occultation measurement over the Antarctic
(Journal of Geophysical Research, 2005-10-26) Amekudzi, L. K.; Sinnhuber, B.-M.; Sheode, N. V.; Meyer, J.; Rozanov, A.; Lamsal, L. N.; Bovensmann, J. P. Burrows
[1] NO3 vertical profiles have been retrieved over the Antarctic (60 –90 S) from the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) lunar occultation spectra, using the visible spectral band (610–680 nm) containing NO3 absorption bands at 623 and 662 nm. The retrieved NO3 profiles agree well with calculations from a photochemical model constrained by retrieved O3 and analyzed temperatures in the altitude range between 24 and 45 km. Below about 35–40 km, observed NO3 is well reproduced by photochemical steady state calculations. Differences between observed and modeled NO3 are within the estimated accuracy of 20–35%, demonstrating the consistency of the NO3 retrieval and model.
Retrieval of Trace Gas Concentrations from Lunar Occultation Measurements with SCIAMACHY on ENVISAT
(ENVISAT, 2007-09-17) Amekudzi, L. K.; Bramstedt, K.; Rozanov, A.; Bovensmann, H.; Burrows, J. P
Sciamachy solar and lunar occultation: validation of ozone, No2 and No3 profiles
(ESRIN, 2007-02) Amekudzi, L. K.; Bramstedt, K.; Bracher, A.; Rozanov, A.; Bovensmann, H.; Burrows, J. P.
Using a global spectra fitting method by the differential optical depth within the radiative transfer and retrieval code SCIATRAN 2.1, vertical profiles of stratospheric traces gases are derived from SCIAMACHY solar and lunar occultation transmission spectra. From solar occultation observations ozone and NO2 profiles have been retrieved, from lunar occultation measurements ozone, NO2, and NO3 profiles have been derived. To access the quality of the SCIAMACHY occultation retrieved products a validation study was carried out, by comparing the retrieved ozone and NO2 profiles to correlative observations of other satellite instruments. These instruments are the Halogen Occultation Experiment (HALOE), the second Stratospheric Aerosol and Gas Experiment (SAGE II), and The third Polar Ozone and Aerosol Measurement (POAM III) . The NO3 profiles are compared with results from a photochemical model scheme. The validation show good results for SCIAMACHY occultation products. In solar occultion, the deviation of ozone is mostly within 0 % to +10 % for ozone and within 20 % for NO2 over a wide altitude range. In lunar occultation, the agreement is +10% to +20 % for ozone and within 20 % ˙ for NO2 in the main part of the profiles. The NO3 results show good agreement with the model outputs within the accuracy of 35 %.
Sciamachy solar occultation: ozone and No2 profiles 2002-2006
(ENVISAT, 2007-07) Bramstedt, K.; Amekudzi, L. K.; Bracher, A.; Rozanov, A.; Bovensmann, H.; Burrows, J. P.
The spectrometer SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) on-board ENVISAT is measuring solar irradiances and Earthshine radiances from the UV to the NIR spectral region in nadir, limb and lunar/solar occultation geometry. Solar occultation measurement are performed during sunrise at northern latitudes (49N to 69N, depending on season). Using an optimal estimation approach with the radiative transfer and retrieval code SCIATRAN 2.1, these measurements are used to derive vertical profiles of ozone and NO2. Precise tangent height information is derived from the scanning over the solar disk. Here we present an almost complete dataset from August 2002 to December 2006, including validation results with independent measurements from other satellites.
The Spatio-Temporal Variability of Rainfall over the Agro-Ecological Zones of Ghana
(Atmospheric and Climate Sciences, 2019-07-26) Amekudzi, L. K.; Atiah, Winifred A.; Quansah, Emmanuel; Preko, Kwasi
Rainfall variability plays an important role in many socio-economic activities such as food security, livelihood and farming in Ghana. Rainfall impact studies are thus very crucial for proper management of these key sectors of the country. This paper examines the seasonal and annual rainfall variability in the four agro-ecological zones of Ghana from the CHIRPS V2 rainfall time series spanning a period of 1981-2015. The rainfall indices were computed with the aid of the FClimDex package whereas the trends of these indices were further tested using the Mann Kendall trend test. The results show good agreement (r ≥ 0.7) between CHIRPS V2 and gauge in almost all portions of country although high biases were observed especially in DJF season over parts of the Northeastern (NE) portions of the country. The mean seasonal rainfall climatology over the country is observed to be in the range of 20 - 80 mm, 60 - 200 mm, 100 - 220 mm and 40 - 180 mm in DJF, MAM, JJA and SON seasons respectively with high intensities of rainfall dominating Southwestern portions of the country. The trend analysis revealed positive trends of consecutive dry days in the Transition, Forest and Coastal zones and negative trends in the Savannah zone of the country. Decreasing trends of consecutive wet days are observed over the Savannah, Transition and Coastal zones whereas increasing trends dominate the Forest zone. Savannah, Forest and Transition zones show weak increasing trends of the number of heavy rainfall days whilst weak decreasing trends are observed over the Coastal zone of the country. Similarly, weak increasing trends of the number of very heavy rainfall days are observed over all the agro-ecological zones except in the Transition zone. It is observed that the annual wet day rainfall total has increasing trend in the Savannah and Forest zones of the country whereas decreasing trends cover the remainder of the zones. The trends of these indices in the agro-ecological zones were all significant at a significant value of 0.05. This paper assessed the performance of the CHIRPS V2 rainfall data over the region and reports on the biases in seasonal rainfall amounts which are limited in previous studies. These findings have adverse impacts on rain-fed agricultural practices, water resource management and food security over the country.
Validation of NO2 and NO from the Atmospheric Chemistry Experiment (ACE)
(Atmos. Chem. Phys., 2008-10-08) Kerzenmacher, T.; Wolff, M. A.; Strong, K.; Dupuy, E.; Walker, K. A.; Amekudzi, L. K.; et.al
Vertical profiles of NO2 and NO have been obtained from solar occultation measurements by the Atmospheric Chemistry Experiment (ACE), using an infrared Fourier Transform Spectrometer (ACE-FTS) and (for NO2) an ultraviolet-visible-near-infrared spectrometer, MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation). In this paper, the quality of the ACE-FTS version 2.2 NO2 and NO and the MAESTRO version 1.2 NO2 data are assessed using other solar occultation measurements (HALOE, SAGE II, SAGE III, POAM III, SCIAMACHY), stellar occultation measurements (GOMOS), limb measurements (MIPAS, OSIRIS), nadir measurements (SCIAMACHY), balloon-borne measurements (SPIRALE, SAOZ) and ground-based measurements (UV-VIS, FTIR). Time differences between the comparison measurements were reduced using either a tight coincidence criterion, or where possible, chemical box models. ACE-FTS NO2 and NO and the MAESTRO NO2 are generally consistent with the correlative data. The ACE-FTS and MAESTRO NO2 volume mixing ratio (VMR) profiles agree with the profiles from other satellite data sets to within about 20% between 25 and 40 km, with the exception of MIPAS ESA (for ACE-FTS) and SAGE II (for ACE-FTS (sunrise) and MAESTRO) and suggest a negative bias between 23 and 40 km of about 10%. MAESTRO reports larger VMR values than the ACE-FTS. In comparisons with HALOE, ACE-FTS NO VMRs typically (on average) agree to ±8% from 22 to 64 km and to +10% from 93 to 105 km, with maxima of 21% and 36%, respectively. Partial column comparisons for NO2 show that there is quite good agreement between the ACE instruments and the FTIRs, with a mean difference of +7.3% for ACEFTS and +12.8% for MAESTRO.

Browsing by Author "Amekudzi, L. K."

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