Data Quality Monitoring in RA I Nairobi Regional Meteorological Center Eng. Henry Karanja

Data Quality Monitoring in RA I The Regional Meteorological Center (RMC) Nairobi is the regional data quality monitoring lead center in region 1 Nairobi has a responsibility of monitoring Surface pressure which was started in In assessment of data quality, the center compare the surface pressure information received from different stations with the first- guess numerical short-term forecast.

Possible sources of errors Coding errors. Incorrect sea-level adjustment for height of barometer. Corruption during transmission. Position errors. Barometric errors: – Wrong calibration. - Faulty barometer etc.

Method used for quality Monitoring monitoring of surface pressure for RA I being carried out at RMC Nairobi is based on the results of the UK Met Office Numerical Weather Prediction (NWP) Model. the UK MET Office runs a six-day forecast twice a day and a two- day forecasts grid point model with a horizontal resolution of 25 km in mid-latitudes with 70 levels in the vertical. the basis of the data quality monitoring is the observation and background (First guess) difference (O-B). Systematic errors from the observations are identified by taking averages of the (O-B) over sufficiently long period (e.g one month). using this method, persistent poor quality observations are detected Besides the difference, calculation of the means and root mean squares (RMS) are analyzed over a six month period to detect stations giving persistent erroneous reports.

Error detection criteria the (O-B) statistics having been obtained i.e. mean, RMS, number of observations and percentage gross errors for all the reporting stations for the six months period, the criteria for error detection are applied as set up in the Global Data Processing System (GDPS) manual. The cut-off values for error detection depends on the availability of data and the length of time being monitored. The monitoring is done on monthly and six-monthly periods, each of which has its error detection criteria.

For six-monthly monitoring: Number of observations = or >40 and one of the following. (i) Mean (O-B) = or >3.5 hPa. Or one of the following (ii) - (a) Standard deviation = or >5 hPa or - (b) Percentage gross error at least 25%. NB: The gross error is defined as an observation that departs from the background by at least 15 hPa.

Dissemination of monitoring report and feedback Mechanism The designated focal point generates six-monthly reports on suspected low quality stations and forwards the report to the WMO secretariat through the Permanent Representative of Kenya with WMO. These reports are distributed by WMO to Members so that they can take appropriate remedial action with the assistance of the national designated focal point. These Members/agencies then report to lead centers and the WMO Secretariat on their remedial efforts.

Effect of Monitoring From the experience of the regional centre, the method of monitoring is effective and in some cases led to the improvement of data quality in the region. However, due to the terrain of some of the affected stations, some stations have not been able to take remedial action to rectify the situation. In such cases, members have been advised to follow the available guidelines in the CIMO guide and other relevant manuals and guides in siting of their stations. monitoring report 2011.doc