World Meteorological Day Poster _pdf format_ - World by sdsdfqw21


									                                                              World Meteorological Day - 23 March 2005
                                                               WEATHER, CLIMATE, WATER AND SUSTAINABLE DEVELOPMENT

                                                                            Weather patterns that can hamper sustainable development
                    Winter Storm                                                                  Winter Anticyclone                                                                                     Summer Rain                                                             Summer Drought
                                                                                                                                                                                                                         1010                                                                                                     1008
                                                                                                            1016                                                                                                                Trough                        1014                                                                1010
                                                                                                                                                                                                                 L                                                                                                             1012

        H                                   L                                                               1018                                                                                                1008                                        1016                                                                   1014
                                                                                                                                                                                                                           1010                       1018
                                                                                                                                                        H                                                                                                                                                                                        1012
                 1020                                                                                                                                   1024          H                                                                              1020
                        1018                    1008                                                                                                                                                                      1012
                                                                                                                                                                                                                                                   1022                         H
                                 1014                  1006                                                                                                                                                                                                                         1028
                                 1012                                                                          1022                                                                                                                                                                    1026
                                                                                       H                                                                H
                                                                                                                                                                                                                                            1024                                          1024                  H
                                                                                                                                                                                                                                                                                             1022                                         1010
                                             1004                                                                  1020                                        1020                       H                                                 H                                                   1020             1020
                                            1000                                 1024                                                                                                                                                                                                                                                       1008
                                                                                                                       1018                                                                     28                                                                                                                      1018
                                            998                                                                                                                                               10                                                                                                                                             1006
                                                                                1020                                        1016                                                                  1026
                                                                                                                                                                                                         1024                                                                                                                                1004
                                        L                                1016                                                      1014                                                                           1022
                                                                  1014                                                                    1012                               1012                                                                                                                                                                 1000
                                                                                                                                   1008          1010                                                                                1018                                                                                                                L
                                                                                                            1004          1006                                               L                                              L
                                                               1012                                                L                                                                                                                                                                                    L

Feature:                                                                                   Feature:                                                                                 Feature:                                                                           Feature:
“Deep” cyclone passing close to south-western Cape. Cold front approach-                   Anticyclone positioned right across South Africa.                                        Ridging anticyclone over the Indian Ocean. Low pressure trough over the            Anticyclone ridging over South Africa. Mid-latitude cyclones passing south
ing Cape Town from the west.                                                                                                                                                        interior.                                                                          of South Africa. Absence of Kalahari heat low.
                                                                                           Expected weather conditions:
Expected weather conditions:                                                               Sinking air throughout. Pollution trapped below inversion.                               Expected weather conditions:                                                       Expected weather conditions:
Cold, windy, rainy weather, with snow on the mountains in the south-western                                                                                                         Widespread rain east of the low-pressure trough. Transport of moisture             Dry air in circulation over South Africa. Sinking air leading to hot conditions
Cape. Flooding can occur, especially over low-lying areas such as the Cape                 Hazards:                                                                                 around anticyclone into interior. In a situation when the pressure over the        over the interior. If these synoptic conditions persist, they can cause vast
Flats.                                                                                     Air pollution.                                                                           interior is much lower and accompanied by a cyclone higher up in the               areas to receive below-normal rainfall. When an area receives below-
Rough sea conditions can threaten ships in the vicinity of the cyclone.                                                                                                             atmosphere, conditions of heavy rain and flooding can occur. Weather               normal rainfall for an extended period, drought conditions are likely.
                                                                                                                                                                                    patterns that bring good summer rains can also produce severe thunder-
                                                                                           Threats to sustainable development:                                                      storms, which can bring flash floods, hail, wind damage and even tornadoes.
Hazards:                                                                                   Rapid urbanisation and dependency on fossil fuels together with industrial                                                                                                  Hazards:
Flooding and strong winds.                                                                 development, have lead to an increase in air pollution over South Africa.                                                                                                   Drought, heatwave.
                                                                                           Ground-level ozone, nitrogen dioxide, carbon monoxide and sulfur dioxide                 Hazards:
Threats to sustainable development:                                                        have significant negative effects on the health of both humans and animals.              Floods, severe thunderstorms (hail, wind, heavy rains and tornadoes).              Threats to sustainable development:
Floods affect some 1,5-billion people worldwide a year and pose a                                                                                                                                                                                                      Drylands cover one-third of the world’s land area. South Africa is considered
threat to life, property and livelihoods. One of the main concerns is                      Challenges:                                                                              Threats to sustainable development:                                                to be a dry country. In dry areas, the main concern is the protection of soil
the growing number of people who are forced to settle on flood                                 Decrease our dependency on fossil fuels.                                             Rain-fed agriculture is sensitive to rainfall characteristics such as the number   and water resources. Poor soil and water management can lead to
plains and other areas prone to flooding.                                                      Find alternative manufacturing methods that are less polluting.                      of rain days, rainfall intensity and length of dry spells.                         degradation of the environment.
                                                                                               Enforce South Africa’s new Air Quality Management Act.
Challenges:                                                                                                                                                                         Challenges:                                                                        Challenges:
    Find alternative sites for people to settle and grow crops.                                                                                                                         Crop insurance.                                                                     Manage soil and water resources optimally.
    Protect flood-plain environments.                                                                                                                                                   Building infrastructure to cater for the possible hazards associated with           Encourage people to use water sparingly.
                                                                                                                                                                                        severe thunderstorms.                                                               Employ correct water-management practices.

                                                       Sponsored by the South African Weather Service                                                                                                                                     Tel: (012) 367 6000
                                                                     GLOSSARY OF METEOROLOGICAL TERMS
                                                                                                                                                                                          CLIMATE CHANGE AND SOUTH AFRICA
                                                                            Narrow zone of transition between AIR MASSES that differ in humidity and/or temperature.                      A Global Overview

                                                                                                                                                                                          According to the “WMO Statement on the Status of the Global Climate in 2003” (, the global mean surface temperature in 2003
                                                                                                                                                                                          was 0.46°C above the 1961-1990 annual average. This value makes 2003 the third warmest year in the instrumental temperature record since 1861
                                                                            COLD FRONT
                                                                                                                                                                                          At the surface, all of the 10 warmest years have occurred since1990. Since the 20th century, the increase in global surface temperature has been
                                                                            A FRONT where the colder AIR MASS is advancing and displacing the warmer AIR MASS. The pass-
                                                                            age of the COLD FRONT is accompanied by a sharp drop in temperature, gusty wind and rain.                     between 0.6 and 0.7°C, while the rate of change for the period since 1976 is roughly three times that for the past century as a whole. The annual
                                                                                                                                                                                          global precipitation in 2003 was also below the 1961-1990 average for the third year in a row.

                                                                                                                                                                                           The maximum size of the 2003 Antarctic ozone hole matched the all-time record size reported for 2000 but, as in 2000, the ozone hole dissipated
                                                                            WARM FRONT                                                                                                    earlier than usual. Furthermore, measurements show that most ozone-depleting substances are decreasing in the lower atmosphere and they
                                                                            A FRONT where the warmer AIR MASS is overriding the colder AIR MASS. As the WARM FRONT                        appear to have reached their peak in the ozone layer in the stratosphere.
                                                                            approaches, temperature and humidity increase and light rain falls across a wide band aligned to the
                                                                            WARM FRONT.
                                                                                                                                                                                                      Some South African historical climate trends
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        Annual Rainfall Trends (1911-2000)

                                                                            ANTICYCLONE (HIGH PRESSURE SYSTEM)                                                                                                                               Annual Mean Temperature Trends (1960-2003)
                                                                            An area of high pressure relative to the surroundings. Air circulation around this system is anticyclonic                  0.3
                                            H                               (anti-clockwise in the southern hemisphere). Weather conditions in this system are typically settled with
                                                                            light winds. An ANTICYCLONE is indicated by an “H” on a weather chart.

                                                                            CYCLONE (LOW PRESSURE SYSTEM)                                                                                              0.1
                                                                            An area of low pressure relative to the surroundings. Air circulation around this system is cyclonic
                                            L                               (clockwise in the southern hemisphere). Weather conditions are usually windy and unsettled with rain.

                                                                            A CYCLONE is indicated by an “L” on a weather chart.                                                                         0

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   Rainfall Trends
                  1008                                                                                                                                                                                -0.1

                                                                                                                                                                                                             Cape Columbine*

                                                                                                                                                                                                                                                                                                            Cape St. Francis*
                                                                                                                                                                                                                                                                                         Cape St. Blaize*

                                                                                                                                                                                                                                                                                                                                                                          Cape St. Lucia*
                  1004                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        Significantly negative trend (5%)

                                                                                                                                                                                                                                                                         Cape Agulhas*

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     Pretoria PUR*
                                                                                                                                                                                                                                                                                                                                Port Elizabeth


                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      Emerald Dale
                                                                                                                                                                                                                                                                                                                                                 East London*



                                                                                                                                                                                                                                                                                                                                                                                                                                                                             Glen College
                  1000                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        No significant trend

                                                                                                                                                                                                                               Cape Town*

                                                                                                                                                                                                                                            Cape Point*

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     Pretoria UP
                                                                            An elongated area of low pressure (in contrast to the circular shape of a CYCLONE). This feature is                                                                                                                                                                                                                                                                                                                                                                                                                                                               Significantly positive trend (5%)



                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   Bela Bela

                                                                            common over South Africa in summer and is characterised by afternoon thunderstorm activity to the

                                                                            east of the TROUGH.
                                                                                                                                                                                                                                            Climate Stations (* indicates significance at 5% level)
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   A study on trends in annual rainfall for the period 1911-2000 shows
            1004                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   that there was not a common trend in rainfall for South Africa as a
            1008                                                            RIDGE                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  whole for this period, but on a regional basis similar trends were
            1012                                                            An elongated area of high pressure (in contrast to the east-west orientated oval shape of an                                                                                                                                                                                                                                                                                                                                                                                                                           evident. Apart from trends in annual rainfall, some places also show
                                                                                                                                                                                          South African climate stations were investigated for trends, for the period 1960 to 2003.
                                           H                                ANTICYCLONE). A RIDGE of high pressure south of South Africa assists in transporting moisture from
                                                                            the Indian Ocean into the interior, while a ridge over land tends to dry out the air by bringing relatively
                                                                                                                                                                                          The vast majority of these stations showed positive trends in their annual mean maxi-                                                                                                                                                                                                                                                                                                                    increases in the longest annual dry spells, for the period 1961-2000,
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   significantly so for the Eastern Cape. In this region there is also a
                                                                                                                                                                                          mum, minimum, and average temperature. In general, the number of days and nights                                                                                                                                                                                                                                                                                                                         tendency for fewer daily rainfall events of high rainfall. In contrast,
                                                                            colder and drier air from the South Atlantic into the interior.
                                                                                                                                                                                          with relatively high temperatures have increased, while there are fewer days and nights                                                                                                                                                                                                                                                                                                                  there are clear indications of the number of bigger daily rainfall
                                                                                                                                                                                          with relatively low temperatures.                                                                                                                                                                                                                                                                                                                                                                        events in the far northern and north-eastern regions, mostly due to
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   the heavy rainfall experienced during 2000.
                                                                            BERG WIND
                                                                            A hot and dry offshore wind blowing from the interior plateau of South Africa to the coast. It is most
                                                           Hot              common in winter when an ANTICYLONE situated over South Africa causes the air to flow down the
                                                                            escarpment and out to sea. The air is warmed by compression owing to an increase in PRESSURE as
                                                                            it drops in altitude toward the coast.
                                                                     Sea                                                                                                                                                                                                                                                                                                                                                                                                                          INVERSION
                                                                                                                                                                                          This is a situation in the atmosphere where temperature increases with height instead of decreasing, as is usually the case. It is most common in the
                                                    Weight of a column of
                                                                            ATMOSPHERIC PRESSURE                                                                                          lower part of the atmosphere during the night and also during winter in South Africa when an ANTICYCLONE dominates the circulation. Air near the
                                                    air above this point

                                                                            The PRESSURE exerted by the gases in the atmosphere. The PRESSURE at any point is determined                  surface gets cooled by the relatively cold ground and sinks into the valleys. This cooler, denser air cannot readily mix with the warmer air above and
                                                                            by the weight of the air above that point. As such, PRESSURE decreases with height.                           so the INVERSION acts like a lid, trapping pollutants and moisture near the surface. This situation often leads to fog and hazy conditions and even
                                                                                                                                                                                          potentially hazardous smog. Over the South African highveld in winter, conditions are usually too dry for the formation of fog, but the large amounts
                                         Ground                                                                                                                                           of air pollutants present can reduce visibility to levels common in fog situations. Such air pollution is also a threat to human health.

                                                                            ISOBAR                                                                                                                                                                                                                                                                                                                                                                                                                                   Warm air
                                      1004                                  A line that joins points of equal ATMOSPHERIC PRESSURE on a weather map. ISOBARS are used to
                                      1000                                  identify weather systems such as CYLONES, ANTICYCLONES, TROUGHS and RIDGES.                                                                                                                                                                                                                              Co                                                                                                                                                                                                                              g
                                                                                                                                                                                                                                                                                                                                                                                       ld                                                                         Air pollutants trapped                                                                                                                           in
                                                                                                                                                                                                                                                                                                                                                                                                                ai                                                                                                                                                                                               nk
                                                                                                                                                                                                                                                                                                                                                                                                                      rs                                                                                                                                                                                     r si
                                                                            CUT-OFF LOW                                                                                                                                                                                                                                                                                                                                 in
                                                                                                                                                                                                                                                                                                                                                                                                                                             ki                                                                                                                                                         ai
                                                                            A low pressure system that lies equatorwards of the main mid-latitude belt of westerly winds. It forms                                                                                                                                                                                                                                                              ng                                                                                                                                                 ld
                                                          Jet stream
                                                                            when a TROUGH becomes elongated to the extent that the tip breaks off and forms a separate                                                                                                                                                                                                                                                                                                                                                                                                                          Co
                                                                            CYCLONE detached from the parent TROUGH. CUT-OFF LOWS are some of the most common
                                                                            weather systems associated with large-scale flooding in South Africa.
                           5 - 10km Above ground level

              s                                      rm
            as                                            air



                                                                            AIR MASS



                                                                            A large body of air extending over hundreds or thousands of kilometres, in which the horizontal
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     South African
                                                                            gradients of temperature and humidity are slight.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        Weather Ser vice                                                                            Tel: (012) 367 6000

To top