describe how weather data is collected

•weather: short term, including: rainfall, cloud cover, changes in the atmosphere

•climate: long term condition over 30 years and a large areas, including: temperature and rainfall

•temperature - maximum and minimum in degrees celsius 

•humidity - %

•precipitation - mm

•sunshine - hours 

•cloud - type and cover

•wind speed - km/h and m/s 

•wind direction - N, S, E, W

•air pressure - millibars 

•measuring the weather 

          •the weather station: where temperature, rainfall, humidity, air pressure, wind direction and velocity, sunshine and cloud cover are measured 

                    •thermometers (in a Stevenson Screen), rain gauge, barometer, wind vane (anemometer and sunshine recorder) 

                              •they have good exposure (away from buildings and trees)

                              •thermometers should be placed in the shade - in a Stevenson Screen 

                              •rain gauges should be away from walls

                              •wind instruments should be clear of walls 

                                        •readings should be taken at the same time each day 

        

      

                    •the Stevenson Screen

                              •slatted sides to allow air flow 

                              •painted white to reflect sun’s heat

                              •double roof to protect form sun’s heat

                              •raised 125cm above the ground to avoid effects of ground surface and heat

                              •private area so animals can’t hack the results 

                              •open external space to avoid influence e.g heat from buildings 

          •equipment in a weather station 

                    •a Stevenson Screen (maximum-minimum and dry-wet bulb thermometers inside), measuring cylinder, rain gauge, Six’s thermometer, wind vane anemometer 

          •measuring temperature

                    •Six’s thermometer

                              •when the temperature rises, the mercury expands and pushes the index on the maximum side and leaves it there 

                              •when the temperature falls, the alcohol contracts and it’s meniscus pulls the index along the tube 

                              •they should be away from sunlight and above the ground

                                        •maximum thermometer 

                                                  •contains the expansion of mercury 

                                        •minimum thermometer

                                                  •contains the contraction of alcohol  

                                                

          •measuring rainfall  

                    •rain gauge 

                              •the funnel is attached to the cylinder, which fits into a larger outside container

                              •it’s 20cm in diameter and 50cm tall, with the bottom half buried into the grass to prevent the sun evaporating the rain

                              •stands vertically to avoid splashes entering in

                              •any snow should be melted first 

                              •it is checked every 24 hours at the same time, as dew may accumulate  

                              •placed in an open space on grass so there is no runoff from trees and etc.

          •measuring relative humidity  

                    •wet and dry bulb thermometers (hygrometers) 

                              •dry-bulb is a glass thermometer which records the actual air temperature 

                              •the wet-bulb thermometer is similar, but is enclosed in a muslin bag, which is dipped in a bottle of water

                              •if the air is unsaturated, water will evaporate from the muslin, cooling the bulb

                                        •the wet-bulb temperature is usually lower unless the relative humidity is close to 100%

          •measuring air pressure 

                    •mercury barometer

                              •as air pressure increases, mercury levels decrease 

                    •aneroid barometer 

                              •the pointer moves to the correct reading of the air pressure

                              •the metal box expands when pressure is low, and is compressed when high  

          •measuring wind speed 

                    •anemometer 

                              •an increase in wind speed increases the speed of the bowls 

                              •there is a ‘threshold’ value to rotate the bowls 

                              •above the ground so the slowing effect on the wind of friction with the ground is minimised 

                              •it has three cups which spin around 

          •measuring wind direction 

                     •wind vane 

                              •shows the direction of the wind 

                              •the tail has more resistance than the small pointer, so a wind will force the tail 

          •measuring sunshine 

                     •sunshine recorder 

                              •this is a glass sphere partly surrounded by a metal frame  

                              •the sun’s rays burn a trace on the card, which is divided into hours and minutes

                              •it should be replaced everyday 

•digital weather recording instruments

          •many transmit data to a computer but data may get lost if it gets wet 

•types of clouds 

          •high clouds (5500m - 14000)

                    •cirrus: white filaments 

                    •cirrocumulus: small ripple elements 

                    •cirrostratus: a transparent sheet, with a halo 

          •medium clouds (2000m - 7000m)

                    •altocumulus: layered, ripple elements, white shading 

                    •altostratus: a thin grey layers allowing sun to pass

          •low clouds (0-2000m)

                    •stratocumulus: layered, a series of rounded rolls with shading (typical pic art) 

                    •stratus: layered, uniform, grey 

                    •nimbostratus: a thick layer with a low base, dark clouds 

                    •cumulus: individual cells, with flat vertical towers 

                    •cumulonimbus: large cauliflower shaped towers with anvil tops 

•cloud cover is measured in oktas (eights)