Abstract
We investigate the trends and variability in Total Column Ozone (TCO) over three Kenyan cities; Nairobi (1.17o S; 36.46o E), Kisumu (0.03o S; 34.45o E) and Mombasa (4.02o S; 39.43o E) from 1985 – 2011 using TCO data from combined multiple satellite-based instruments to create a single near-global daily time series. Monthly, annual and seasonal means are calculated based on the measures of TCO daily values. A visual depiction of the trends and variability in TCO is provided by means of the time series. Annual, monthly and seasonal trends in TCO are calculated from straight line fits whereby the net ozone changes over the 27 years analysis can be determined. Quantification of the observed changes in TCO percentage variability is also calculated. Annual means and standard deviations of TCO estimated at Nairobi, Kisumu and Mombasa are 254.75 ± 5.17 DU, 253.92 ± 5.20 DU and 257.07 ± 4.70 DU respectively. Over the period 1985 – 2011 a decreasing trend of 0.031% year -1 is observed at Nairobi, 0.026% year -1 at Kisumu and 0.031% year 1 at Mombasa equating to losses of 2.158 DU at Nairobi, 1.759 DU at Kisumu and 2.164 at Mombasa. TCO annual variability ranges between 1% and 6%, while the seasonal variability ranges between 2% and 4%. The slope of the line of fit exhibit a negative sign showing a statistically decreasing trend over time in all the three locations under study, hence, temporal variability of TCO in all the three cities is declining.
Highlights
The atmosphere, which consists of the lower, middle and upper atmosphere levels, is the transition zone between earth and space made up of a mixture of gases
We investigate the trends and variability in Total Column Ozone (TCO) over three Kenyan cities; Nairobi (1.17o S; 36.46o E), Kisumu (0.03o S; 34.45o E) and Mombasa (4.02o S; 39.43o E) from 1985 – 2011 using TCO data from combined multiple satellite-based instruments to create a single near-global daily time series
The trends derived from linear fits to the monthly mean TCO time series from 1985 – 2011 are shown in Figures 1(a) – (c)
Summary
The atmosphere, which consists of the lower, middle and upper atmosphere levels, is the transition zone between earth and space made up of a mixture of gases. These gases are exposed to the sun’s electromagnetic spectrum. The Global Climate Observing System (GCOS), in their report (GCOS, 2010), identified Total Column Ozone (TCO) to be among the fifty Essential Climate Variables (ECVs). Both stratospheric depletion and tropospheric excess of ozone are harmful to the biosphere. This calls for the monitoring of ozone concentration variations and trends in both the stratosphere and troposphere
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