THE DYNAMICS OF TEMPERATURE, EVAPORATION AND WIND MINGGU 4: VARIASI KOMPONEN IKLIM TROPIS THE DYNAMICS OF TEMPERATURE, EVAPORATION AND WIND

WEEKLY SST TH. 2006

WEEKLY SST TH. 1997

WEEKLY SST TH. 1998

VARIASI SUHU UDARA DI DATARAN TINGGI CEKUNGAN DANAU VICTORIA (0021’ N – 300’ S; E), Kericho (Kenya), Kabale (Uganda) and Bukoba (Tanzania).

Temporal variation of maximum temperature, rainfall and malaria epidemic anomalies between January 1997 and December 2001 in the highlands of Lake Victoria basin (0021’ N – 300’ S; E). Kericho (Kenya), Kabale (Uganda) and Bukoba (Tanzania). UCL : Upper Climatic Level; LCL: Lower Climatic Level;

ATMOSPHERIC MOISTURE Importance of Water Vapor Water vapor constitutes 0–4% of the total volume of the atmosphere, yet it is the most important determinant of weather and climate, some processes that are critical to weather and climate in the tropics. First, water vapor condenses to form precipitation, an essential resource for life. The potential for precipitation is determined by the amount of water vapor. Keep in mind that entire economies in parts of the tropics depend on an adequate supply of fresh water. Second, water vapor is an active absorber and emitter of infrared (IR) radiation, thereby affecting heating and cooling of the atmosphere and surface. Third, latent heat release when vapor condenses or freezes is an important energy source for atmospheric motion and convective weather systems. Fourth, vertical transport of water vapor, through cumulus convection, is the most important mechanism for upward transport of heat in the tropics. Water vapor enters the atmosphere through surface evapotranspiration, whereby latent energy is absorbed. When the vapor condenses or freezes, the latent heat is released to the atmosphere. Fifth, the amount of water vapor influences the rate of surface evaporation and transpiration. Humans and other animals are uncomfortable in highly humid conditions that impede the rate of perspiration. Conversely, very low humidity leads to dehydration and related health problems. Furthermore, water is constantly changing phases within the range of normal atmospheric temperatures, which is unlike other atmospheric gases.

Moisture processes critical to weather and climate The phases of water and latent heat exchange

Sources of Water Vapor: Evaporation and Evapotranspiration Evaporation from the ocean is the primary means by which water and energy are transported from the surface to the atmosphere. The tropics drive the global energy and water cycle since the oceans, which comprise most of the tropical surface, receive a surplus of radiative heating. The significance of the tropical ocean as a source of water vapor is easy to imagine if you consider that the Pacific Ocean alone spans nearly one half of the earth’s circumference at the equator. While evaporation over land is less than that over the ocean, its distribution plays a vital role in the initiation and evolution of convective weather systems. Tropical forested regions, like the Amazon, are significant sources of water vapor. Following methods first introduced in the 1940s, evaporation over the ocean is estimated by an empirically-derived equation: The coefficient Cw is altered to allow for very light winds (e.g., over the Tropical Pacific where the wind is near zero). Evaporation can be measured using eddy correlation or eddy covariance techniques and relative humidity sensors that record changes on highly turbulent scales (sometimes less than 1 second). Evaporation rates are also estimated from satellite microwave sensors, which detect radiation emitted by water vapor. Standards for measurement of evaporation are provided by the WMO. Where would you expect evaporation rates to be high? Select all that apply. a. Everywhere along the equator b. Over warm ocean currents c. Where wind speeds are higher d. Where the relative humidity is highest

EVAPORATION: On average, regions equatorward of 30º latitude have much higher evaporation rates than higher latitude zones, a distinguishing feature of the tropics. The highest evaporation rate occurs along the western side of the subtropical oceans during the winter when cold, dry continental air flows over warmer ocean currents such as the Gulf Stream and Kuroshio. Stronger surface winds in winter also contribute to higher rates of evaporation. Evaporation rates increase in the inflow areas of hurricanes and where storms increase the wind speed over the ocean. Deep convective clouds increase the rate of evaporation because of the wind speed. Why are evaporation rates so low along the equator, where solar heating is at the maxi-mum? The lowest rates are found above cold currents and upwelling regions such as the equatorial eastern Pacific. The latter is due to reversal of the sign of the Coriolis acceleration. Another reason is that deep convective clouds reduce the amount of solar radiation. Wind speed and ocean transport are also partly to blame; low wind speeds in the equatorial oceans reduce the evaporation rates. Mean annual evaporation rate (cm yr-1) for 1958 to 2005 (from the OAFlux Dataset, Woods Hole Oceanographic Institute). Dotted lines mark ±30º.

EVAPOTRANSPIRATION Another source of water vapor is transpiration, the process by which water vapor enters the atmosphere through the stomata in the leaves of plants. The contribution of water vapor from evaporation and transpiration combined is known as evapotrans-piration (ET) and represents an important part of the water cycle. ET rates for amply-watered plants are determined by: Incoming radiation: ET rates increase as incoming radiation increases Temperature: ET rates increase as temperature rises until an optimum temperature is reached. The optimal temperature varies by type of plant, with tropical plants typically having a higher optimum temperature than those at higher latitudes. As temperature increases above the optimum temperature, the ET rates decrease. Relative humidity: ET increases with the relative humidity gradient. The bigger the moisture gradient between the surface and the air, the higher the ET. As the relative humidity of the air rises, ET rates fall. Other things being equal, it is easier for water to evaporate into drier air than more moist air. Wind: Increased wind speed results in a higher ET rate in unstressed plants. With little movement of the air, water saturates air surrounding leaves or the air above water surfaces. With movement, saturated air is replaced by drier air. Note that evaporation happens even under calm conditions. Soil moisture availability: When soil moisture is lacking, plants transpire less, and can even wilt when the soil is very dry. Type of plant: Transpiration rates vary among plants. For example, plants in arid regions conserve water by transpiring less.

Potential evapotranspiration is a measure of the maximum possible water loss from an area under a specified set of weather conditions. Maximum annual potential evapotrans piration occurs where temperatures are highest in regions such as the Sahara Desert. Values are very low where temperatures are low and vegetation is sparse, such as the Tibetan Plateau. Rates are relatively low where the surface-to-atmosphere moisture gradient is weak and relatively high where that gradient is strong. Evaporation pans and lysimeters are two common methods used to measure the poten- tial evapotranspiration, which often greatly exceeds the actual ET. Mean annual potential evaporation (Wm-2) for January 1948 to December 2006 (from NCEP-NCAR Reanalysis, NOAA CDC).

Pola Gerakan Udara di Sekitar Equator Samudera Hindia Pola gerakan angin di wilayah bagian utara ekuator ( 00 – 2,50 LU ) pada bulan Januari dan Februari arah angin dari Barat Daya ke Timur Laut dan terjadi pusaran pada posisi 00 LU – 2,50 LU dan 900 BT – 950 BT. Pada bulan Maret dan April dominasi arah angin dari Barat ke Timur menuju wilayah Sumatera Barat. Pada bulan Mei sampai dengan Oktober dominasi arah angin dari Barat Daya ke Timur Laut. Selanjutnya pada bulan November arah angin dari Barat ke Timur menuju wilayah Sumatera Barat, sedangkan pada bulan Desember dari Barat membelok ke Timur Laut dan terjadi pusaran pada posisi 00 LU – 2,50 LU dan 900 BT – 950 BT. Pola gerakan angin di wilayah bagian selatan ekuator ( 00 – 50 LS ) pada bulan Januari dan Februari arah angin dari Barat berbelok ke Tenggara. Pada bulan Maret dan April dominasi arah angin dari Barat ke Timur menuju wilayah Sumatera Barat. Pada bulan Mei sampai dengan Oktober dominasi arah angin dari Tenggara berbelok ke Timur Laut. Selanjutnya pada bulan November arah angin dari Barat ke Timur menuju wilayah Sumatera Barat, sedangkan pada bulan Desember dari Barat membelok ke Tenggara.

Arah dan Kecepatan Angin Rata-rata Bulan Januari PERGERAKAN ANGIN Arah dan Kecepatan Angin Rata-rata Bulan Januari

Arah dan Kecepatan Angin Rata-rata Bulan Februari

Arah dan Kecepatan Angin Rata-rata Bulan Maret

Arah dan Kecepatan Angin Rata-rata Bulan April

Arah dan Kecepatan Angin Rata-rata Bulan Mei

Arah dan Kecepatan Angin Rata-rata Bulan Juni

Arah dan Kecepatan Angin Rata-rata Bulan Juli

Arah dan Kecepatan Angin Rata-rata Bulan Agustus

Arah dan Kecepatan Angin Rata-rata Bulan September

Arah dan Kecepatan Angin Rata-rata Bulan Oktober

Arah dan Kecepatan Angin Rata-rata Bulan November

Arah dan Kecepatan Angin Rata-rata Bulan Desember

( Januari, Febuari, Maret, April, dan November ) Pola Gerakan Udara Rata-Rata Bulanan Arah angin dari barat ke timur menuju Wilayah Sumatera Barat ( Januari, Febuari, Maret, April, dan November )

Arah angin tidak menuju Wilayah Sumatera Barat Pola Gerakan Udara Rata-Rata Bulanan Arah angin tidak menuju Wilayah Sumatera Barat ( Mei, Juni, Juli, Agustus, September, dan Oktober )

Desember, di sekitar ekuator dari barat ke timur menuju Sumatera Barat, di selatan ekuator dari barat ke tenggara, di utara ekuator dari timur laut

Computer models [Image 1] The main tool for both past and present climate analyses are computer climate models. Much like the models used to forecast weather, climate models simulate the climate system with a 3-dimensional grid that extends through the land, ocean, and atmosphere. The grid may have 10 to 60 different levels in the atmosphere and surface grid spacings of about 60 by 90 miles (100 by 150 km)—the size of Connecticut. The models perform trillions of calculations that describe changes in many climate factors in the grid. [click, Image 2] The models project possible climates based on scenarios that cover a range of assumptions about global population, greenhouse gas emissions, technologies, fuel sources, etc. The model results provide a range of possible impacts based on these assumptions.

A Seamless Climate Prediction Framework Forecast Lead Time Climate Change. Forecast Uncertainty Centuries Scenarios Decades Anthropogenic Forcing Climate Variability Outlook Prediction Years Seasons Guidance Months Boundary Conditions Threats Assessments Weather 2 Weeks 1 Week Forecasts Initial Conditions Days Watches Hours Warnings & Alert Coordination Adapted from: NOAA Minutes Applications Energy Health State/Local Planning Protection of Life & Property Space Applications Water Management Fire Weather Hydropower Recreation Ecosystem Commerce Agriculture Environment Transportation Water Resource Planning

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