Quality considerations on meteorological parameters to be used for modelling UV-radiation Tor Håkon Sivertsen Bioforsk Plant Health and Plant Protection, Hogskoleveien 7, N‑1432 Aas (Norway); e-mail:tor.sivertsen@bioforsk.no Whereas central national weather bureaus are responsible for the weather forecasts and climatic monitoring in most countries, the responsibility of an agricultural weather service could belong to agricultural research organisations or even extension services. When the agricultural sector is small compared to other ones of the national economy, the warning system may be better served by a weather station station network specially tailored to collect data from agricultural areas and not so well by a national network for weather forecasting and climatic mapping. A close connection between the agricultural and meteorological units is, however, very significant for the agricultural research as well as for the incorporation of agricultural weather recordings from the network into the national database.

Connection to COST 726 The main objective of COST ACTION 726 ‘Long term changes and climatology of UV radiation over Europe’ is to advance the understanding of UV radiation distribution over Europe as well as understanding the UV changes. Among the practical objectives is advancement of understanding UV reconstruction models for the calculation of UV climatology. Relationships between climatic factors and disease development have been studied in numerous plant diseases for decades. For many years results have been presented as models. Today warning systems are nearly always computerized models or other formalized procedures.

The engagement of Norwegian Institute for Agricultural and Environmental Research in COST ACTION 726 The practical contribution from the institute is providing data from a network of automated agro meteorological stations, as well as providing know how connected to administration of data and integration of data from different sources. The network of agro meteorological stations was established in 1987. 51 of the stations are measuring global radiation, hourly values of this parameter.

Data of interest for modelling UV radiation at the ground I just mention some known facts. Data of interest are parameter values describing the spatial and temporal distribution of short wave radiation from the sun. It is also necessary to have information on values of parameters describing the physical and chemical properties of the column of air above the ground.

Relevant data measured at the network of agro meteorological stations The data from these stations are hourly parameter values. The following parameters are of interest: Global radiation, amount of precipitation, temperature of the air, albedo, hours with direct sun radiation and relative humidity of the air.

We model the nature by using parameters connected to the phenomena We model the nature by using parameters connected to the phenomena. Each of the parameters of the models has a ‘name’, it has a ‘definition’ and it has a ’unit’.

To actually use the model we must have input parameters we must have some sort of system for making measurement. Each parameter we derive through the system for making measurement has a ’name’, it has a ‘unit’, it has a ‘definition’. The parameter value derived is connected to the method for making measurements and we want it to be representative for the model parameter considered.

Macro physics The macro model of the air we may conceptually describe as a parcel of air (the mass is not clearly defined, merely the relative mass, the density); and connected to this parcel we have the quantitative parameters.  

  We may then extend our model by connecting spatial and temporal coordinates to each parcel of air (by using f.ex. Cartesian coordinates x,y,z and the time coordinate t) These coordinates are in fact parameters connected to each parcel of air. Two different mathematical systems have been developed for studying flow of parcels of fluid: The representation of Joseph Louise Lagrange, looking at tagged parcels of fluid, and the representation of Leonard Euler,looking at the parameter values of the fluid parcels as function of the spatial and temporal coordinates.

We may connect parameters, measurable quantities to the Micro physics There also are developed models of the molecular physics of the air, looking at the movements of the molecules. This may be considered a quite different world with quite different phenomena: Molecules, space, time   We may connect parameters, measurable quantities to the phenomena of the microphysics. And through statistical physics macro properties of the air may be derived. .

Micro physics   Examples of parameters connected to the microphysics of the air: Molecular mass, velocity of a molecule, momentum of a molecule, angular momentum of a molecule, spatial coordinates (x,y,z), temporal coordinate t.   An interesting feature in this is that the temporal and spatial coordinates of the macro-physics and the micro-physics should not be the same. We consider two quite different worlds.

Physical ‘laws’   The parameters of the macro state, we connect to certain ‘physical laws’ or preliminary hypotheses containing combination of the parameters: Conservation of mass Conservation of energy ( containing The first law of thermodynamics). Conservation of momentum The second law of thermodynamics giving us the direction of certain processes.  

Physical ‘laws’ We are able to use the laws of classical thermodynamics (the concept of reversible processes) for the parcels of air. We are able to use Newtons laws of motion for each parcel of air (and we call it convective flow). We then look at the fluid system as two different interrelated processes going on simultaneously on two different scales, the molecular movements of the air and the convective movements of the air

Most of the parameters used in meteorology and in meteorological models I think, might be derived from physical concepts of classical thermodynamics, fluid dynamics and the radiation ‘laws’ of short wave and radiation.   Also changes of phase of the water of the parcels of air are included in this –water vapor – drops of liquid water – crystals of ice.

Examples of meteorological parameters connected to the ‘physical laws’ mentioned:   Instant temperature of the air 2m above the ground Hourly mean temperature of the air 2m above the ground Daily mean temperature of the air 2m above the ground Monthly mean temperature of the air 2m above the ground Instant air pressure at the sea surface Instant relative humidity of the air 2m above the ground Hourly mean of the relative humidity of the air 2m above the ground Daily mean of the relative humidity of the air 2m above the ground Monthly mean of the relative humidity of the air 2m above the ground

We then move on to the practical systems for making measurements of meteorological parameters: Networks of meteorological stations, weather radar systems, satellites, radio sond systems  

Agro meteorology Agro meteorological phenomena are combinations of meteorological and biological phenomena. The biological phenomena also may be describes by connecting measurable parameters to the phenomena: Leaf area index of a crop canopy, weight of the biomass etc.