خشکسالی در خاور قاره ی آفریقا Drought in East Africa

East Africa is about as far from the Central Pacific Ocean as a person can get without leaving the planet. And yet, as the Pacific chills, drought grips East Africa in classic La Niña style. Because of global teleconnections, La Niña has to power to affect the weather half a world away.

This image, from France’s SPOT satellite, shows severe drought in Somalia, Kenya, and southern Ethiopia. The image is a vegetation anomaly, a measure of how well plants were growing compared to average. This image compares plant growth between January 1 and 10, 2011, compared to the average growth for January between 1999 and 2009. Widespread brown is an indication that plant growth slowed, with fewer photosynthesizing leaves than average.

A typical December in much of East Africa is rainy, the end of a 3-month rainy period before a dry stretch that usually lasts from January to March. In 2010, however, the rains were erratic and ended in early November. December was hot and dry. Two thirds of Somalia received less than 75 percent of normal rainfall, reported the UN-funded Somalia Water and Land Information Management program. Without rain, the pastureland and cropland in the region produced poor crops and little grass for livestock, leading to food shortages and livestock deaths, said the United Nations.

Poor or failed rainfall during the short rain growing season (October to December) is a classic La Niña signal. In late 2010, a strong La Niña cooled surface waters in the central and eastern Pacific Ocean, while allowing warmer water to build in the eastern Pacific. The pool of warm water in the east intensifies rains in Australia, the Philippines, and Indonesia. Domino-style, this pattern also increases the intensity of westerly winds over the Indian Ocean, pulling moisture away from East Africa toward Indonesia and Australia. The result? Drought over most of East Africa andfloods and lush vegetation in Australia and other parts of Southeast Asia.

1.   References

2.   Anyamba, A., Tucker, C.J., Mahoney, R. (2002). El Niño to La Niña vegetation response patterns over East and Southern Africa during 1997-2000 period. Journal of Climate, 15, 3096-3103.

3.   Ropelewski, C.F., Halpert, M.S. (1987) .Global and regional scale precipitation patterns associated with the El Niño/Southern Oscillation. Monthly Weather Review, 115, 1606-1626.

4.   Somalia Water and Land Information Management. (2011, January 17). Somalia drought watch. Published on ReliefWeb. Accessed January 19, 2011.

5.   United Nations Office for the Coordination of Humanitarian Affairs. (2011, January 13). La Niña drought response by sectors. Published on ReliefWeb. Accessed January 19, 2011.

مه بر فراز دریاچه ی بایکا ل Fog over Lake Baikal

Fog is essentially a cloud that exists near the Earth’s surface, and fog can form over land or water. On September 22, 2011, fog formed over Lake Baikal in southeastern Siberia, and the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this natural-color image the same day.

The fog almost perfectly mimics the lake’s area, only thinning at the southwestern end, and leaving a few parts of the water surface fog-free. When cold air flows over warm water, some surface water evaporates into the cold air and saturates it, raising its relative humidity to 100 percent. The phenomenon is alternately known as evaporation fog, steam fog, even sea smoke, explains Michael Pidwirny of the University of British Columbia. Meteorologists define the existence of fog as visibility of less than 1 kilometer (0.6 miles) at ground level.

Lake Baikal is 25 million years old and about 1,700 meters (5,600 feet) deep, making it the world’s oldest and deepest lake. It holds about 20 percent of Earth’s unfrozen fresh water, according to the United Nations Educational, Scientific and Cultural Organization (UNESCO). The lake is a UNESCO World Heritage Site.

1.   References

2.   Pidwirny, M. (2008, June 19). Precipitation and fog. The Encyclopedia of Earth. Accessed September 23, 2011.

3.   World Heritage. (2011). Lake Baikal. UNESCO. Accessed September 23, 2011.

گرد وغبار درباختر آفریقا Dust off Western Africa

Dust plumes blew off the west coast of Africa and over the Atlantic Ocean in late September 2011. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this natural-color image on September 23, 2011.

The dust plumes sport a wave-like appearance—bands of thick dust alternating with bands of relatively clear air. Some waves extend westward while others curve toward the south in giant arcs. At the end of one curving wave of dust, a line of clouds extends southward over the sea. These ribbon-like patterns might result from atmospheric waves.

Sand seas sprawl over much of Mauritania, and the abundant sand provides plentiful material for dust storms. This dust storm has not yet reached Cape Verde, which lies to the southwest, but the dust appears headed in that general direction.

1.   References

2.   Haynes, J. (2009, July 20). Weather: Avoiding Turbulence. NASA Science. Accessed September 23, 2011.

شکل چرخشی رودخانه به سبب برخورد شهابسنگ The Wembo-Nyama Feature - Democratic Republic of Congo

This circular feature could be one of the largest asteroid impact sites on Earth

 

What Earth Processes Produce Circular Features? In the center of the Democratic Republic of Congo, the Unia River flows around a circular structure known as the Wembo-Nyama feature. Several things in nature leave a circular footprint such as this, including volcanoes and uplifted domes. However, Italian scientists from the University of Padova believe that the Wembo-Nyama feature is an impact crater. If the 36–46-kilometer-wide feature is a crater, it is among the largest in the world.

فوران های آتشفشان ِ " رابا ل " Rabaul Volcano Erupts (in 1999)

An ash plume rises from Tavurvur Volcano (part of the Rabaul Volcanic Complex) on November 19, 1999. NASA/USGS Landsat 7.

There are some amazing things buried in the archive, like this natural-color image of an eruption at Rabaul. According to the Global Volcanism Program the activity at the time was “continuous, forceful emissions of thick, light-to-dark gray ash cloud

آتشفشا ن " نابرو " وآتش سوزی Nabro Volcano and Texas Wildifres

This long-dormant Eritrean volcano began erupting in June, but it’s so remote (at least for western media and scientists) that there’s been no news from the area for months. Unfortunately it’s often been cloudy, so we haven’t gotten any good satellite imagery, either. The best recent imagery is this false-color image (vegetation is red), which shows activity has ceased, although there may be a slight hint of gas emissions near the vent. We’re still trying for better imagery, and will post anything we get in our Volcanoes and Earthquakes

جریان گدازه در آتشفشان " کیزی من " Lava Flow on Kizimen Volcano

A prominent lava flow descends the eastern flank of Kamchatka’s Kizimen Volcano in this false-color satellite image acquired on September 5, 2011 (top). An image of the peak from September 6, 2009 (lower), shows the extent of the changes that have occurred since Kizimen began erupting in late 2010.

Volcanic deposits (colored brown) have covered much of the vegetation (red) on the slopes of the volcano, especially to the east. Likewise, material has filled rivers and streams around the volcano. A modest volcanic plume rises from Kizimen’s summit, accompanied by a smaller plume from a fumarole to the northwest.

These images illustrate the growth of a stratovolcano: layers of lava flows alternate with layers of “volcanic ash, cinders, blocks, and bombs.” Unlike fluid hawaiian-style lava, the flow on Kizimen is a block-lava flow, so viscous it’s almost solid. As the flow slowly advances down the east side of the volcano, the surface crumbles, sending boulders, rocks, pebbles, and other material tumbling into the valley below.

In less than a year, this rubble piled high enough to block several drainages, and a new lake was formed. Ash and fine sediment color the lake brilliant blue, in contrast to the nearly black shade of the lake in 2009. Famous stratovolcanoes include Mount St. Helens, Mount Fuji, and Popocatepetl.

These images were acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) aboard the Terra satellite.

1.   references

2.   Global Volcanism Program. (2011, September 7). Kizimen: Weekly Reports. Accessed September 12, 2011.

3.   Kamchatka Volcanic Eruption Response Team. (2011, September 8). Kamchatkan and Northern Kuriles Volcanoes.Accessed September 12, 2011.

4.   USGS Cascades Volcano Observatory. (2005, October 5). DESCRIPTION: Composite Volcanoes and Stratovolcanoes, Subduction-Zone Volcanoes.Accessed September 12, 2011.