REVIEW OF SPRING 1991 IN THE NORTHERN HEMISPHERE

IMPORTANT CLIMATOLOGICAL EVENTS

The Meteorological Research Flight went out to Kuwait in April to sample the at- mosphere near the oil fires. The maximum concentration of particles was at about 6000ft with only a trace of pollution reaching 25000ft. It appears that the pollution is likely to be washed out or will fall out relatively close to source and it seems unlikely that it will reach the stratosphere and thus affect the global climate.

The amount of ozone in high northern latitudes was the lowest ever recorded (north- ern Finland). Scientists from the British Antarctic Survey estimate that there has been a decrease of about 8 per cent in February and March compared with measurements in previous years.

The mean Central England Temperature (CET) for March is 6.2"C for the decade 1981-90 compared with 5.2"C for the whole 333-year period of the CET record.

The Department of the Environment has issued maps of Britain showing areas most affected by pollution. Areas of Wales and Scotland are suffering acutely from acid rain.

Damaging frosts in the vine-growing regions of France in April, especially the Bor- deaux and Champagne districts, are likely to result in a low yield of grapes this year.

MARCH On the 5OOmbar monthly mean chart the circumpolar vortex was centred over the

Canadian archipelago. The jet stream was stronger than usual over the western North Pacific and over Asia while that in the western North Atlantic was further south than normal. Anomalously high 500mbar heights over Scandinavia gave a European ridge between 10 and 20"E. The normal Rockies ridge was displaced westwards into the eastern Pacific.

On the monthly mean surface chart the Iceland low was displaced into the central North Atlantic. An anomalous south-easterly flow covered much of Europe.

In contrast to February, it was a relatively warm month over Europe, the Mediterra- nean and north Africa with monthly mean temperatures 3degC above normal in some places. Further east over much of the USSR and Asia north of 30°N, the month was cooler than average with anomalies of -6degC in central Siberia. Apart from areas near the west coast, almost the whole of North America had mean temperatures well above normal.

It was a wetter than average March over Scandinavia, west and north Britain, Iberia and much of north-west Africa but central and eastern Europe and western USSR had a

.drier month than normal. In the Middle East rainfall was exceptional, over 600 per cent of normal being re-

corded in Saudi Arabia, Israel and other areas adjacent to the Gulf War area. There was also some severe flooding in south-east Iran late in the month.

Pink-grey dust originating in Algeria and Morocco fell in parts of western Britain on the 8th.

Central England Temperature 7.9"C (t-2.3degC) England & Wales Rainfall (provisional) 72.6mm (123 per cent)

APRIL

The circumpolar vortex on the 5OOmbar monthly mean chart was centred over the Siberian Arctic. In the North Atlantic the jet stream was veered some 20 degrees from its normal direction and was stronger than usual. There was a poorly defined upper trough near l5"E and the usual Canadian trough was displaced into the west Atlantic at about 50- 55"W.

The North Pacific jet stream was also unusually strong. On the monthly mean surface chart there was a low in the Siberian Arctic while both the Iceland and Aleutian lows were deeper than average with the former displaced well to the east of its usual position. Pressure was abnormally high over much of Eurasia and the Atlantic around 50"N.

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It was a warm April over Scandinavia, western USSR, the Middle East and north-east Asia including Japan, but most of Europe and also the Siberian Arctic were colder than the April mean. Rainfall was above average in western Britain, south-east Europe and around the shores of the Mediterranean whilst much of continental Europe and central Asia was drier than usual. Almost all of North America except for north-east Canada had another warm month but it was rather wet except in California and Canada north of 55"N.

A series of damaging tornadoes occurred in the mid-west USA with many lives being lost. In much of southern England the 29th was the wettest April day of the century.

A very severe cyclone struck Bangladesh at the end of the month and this was followed by several tornadoes and heavy rain leading to a total loss of at least l3OOOO lives.

Central England Temperature 7.9"C (-0.1degC) England & Wales Rainfall (provisional) 71.9mm (124 per cent)

MAY

The most important feature on the 500mbar monthly mean chart was the strong meridional pattern from eastern North America across the Atlantic into the USSR; 500mbar heights were nearly 20 decametres above average to the west of Ireland and 10 decametres above average near the Great Lakes and east of Moscow with strong troughs near 50"W and 20"E. The jet stream continued to be very strong between 40 and 50"N across almost the whole of the North Pacific.

On the monthly mean surface chart the Azores high was displaced close to south-west Ireland while the Iceland low moved westwards into the Davis Strait. Low pressure covered the North Pacific from the Aleutians to east Asia. It was a warm May over most of Asia and North America except in some western states of the USA, but the central Mediterranean countries and most of eastern Europe were notably cool and unsettled.

Central England Temperature 11.2"C (-0.1degC) England & Wales Rainfall (provisional) 14.9mm (22 per cent) (driest since 1896)

SPRING AS A WHOLE All three spring months were notably warm over much of North America except for

north-east Canada and some western states of the USA. Over Eurasia temperatures were more variable but much of Europe had predominantly rather cool weather in the second half of spring.

There were some notable rainstorms in the Middle East in March and damaging tornadoes in the USA in April. The Bangladesh cyclone and the following floods and storms were some of the worst ever experienced.

Central England Temperature England & Wales Rainfall (provisions[)

9.0"C (+0.6 degC) 159.4mm (90 per cent)

R. A. S. RATCLIFFE

NEWS

A former Editor of Weather, Emeritus Professor C . E. Wallington, has been awarded the Order of Australia for his work in aviation meteorology and air sports. A few years ago he was also elected Fellow of the Australian Academy of Technological Sciences and Engineering. During his period as Editor of Weather, from 1963 to 1965, he designed and introduced the Weather Log and the Metmap. Now, in so-called retirement, 'Wally' (as he is known in many countries) is very actively involved in meteorological field studies, gliding and ballooning. He also chairs the scientific (mainly meteorological) half of the International Organisation for the Science andTechnology of Air Sports, and is currently writing a new book on Meteorology for air sports.

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C. E. WALLINGTON AWARDED ORDER OF AUSTRALIA