Physics Today Daily Edition
CNN: India is experiencing its worst drought in decades. Exceptionally high temperatures some 3–5 °C above average over the past year and two years of below-average rainfall have severely reduced groundwater levels. According to India's Central Water Commission, the country's major water reservoirs are 79% empty, and three-quarters of the country's basins have less water than the 10-year average. They are so depleted that the next monsoon season, which begins in June, will likely not be enough to fully replenish them, says Nitya Jacob of WaterAid India.
Mashable: On Friday, researchers from the Johns Hopkins University Applied Physics Laboratory released the first full-planet mapping of elevations on Mercury. The map was produced from data collected by the MESSENGER spacecraft, which finished its mission roughly one year ago. To produce the map, the scientists used more than one-third of the 300 000 images of Mercury taken by MESSENGER. From the images, the researchers calculated the average ground level and then measured the lowest and highest points on the planet, with the lowest point being 5.38 km below the average and the highest point 4.48 km above the average.
New York Times: Generally a postdoctoral position is a stepping stone to a full-time position in academia, but academic positions are hard to come by because of low turnover and high competition. So why do so many doctoral students in the sciences pursue postdocs? In 2010 and again in 2013, Henry Sauermann of Georgia Tech and colleagues surveyed PhD students studying biological and life sciences, physics, chemistry, engineering, or computer science at 39 universities across the US. They found that more than three-quarters of the biological and life sciences students believed at least one year of postdoctoral research was necessary to apply for a faculty position, and by 2013, 74% had taken a postdoc position. In the other fields, 42% thought a postdoc was necessary for a faculty position, and 46% took a postdoc by 2013. The most common reason cited by students for taking a postdoc was to increase their chances of getting a desired job.
Science: For several decades, unusual radar signals have been spotted that appear at dawn at an altitude of 150 km, grow stronger as they descend to 20 km, and then rise back to 150 km before disappearing at sunset. Because the signals get weaker during solar eclipses and stronger during solar flares, the Sun may be the source of the effect. But what causes it has not been clear. Now Meers Oppenheim and Yakov Dimant of Boston University suggest that extremely high-energy solar UV radiation could be ionizing gas molecules in a thin band of the upper atmosphere at an altitude of 150 km. Earth's magnetic field would then cause the freed electrons and the ionized molecules to rearrange themselves into areas of varying density, which can be detected by radar.
Gizmodo: The magnitude 5.8 earthquake that struck northern Virginia in 2011 was notable because of the extreme rarity of earthquakes in that region—it was the strongest earthquake east of the Rocky Mountains since 1944. The East Coast of the US is far from the edges of the North American tectonic plate, where interactions with neighboring plates trigger seismic activity. Now Berk Biryol of the University of North Carolina at Chapel Hill and colleagues believe they have found an explanation for the 2011 earthquake. Biryol's team used seismic activity from around the globe to construct a 3D map of the bottom of the North American plate. The researchers found that the southeastern part of the plate is heavily fractured and encompasses thin and thick sections of crust and mantle. Based on their map, the scientists argue that chunks breaking off the bottom of the plate could trigger earthquakes. The mechanism could explain other major seismic events such as the magnitude 8.1 earthquake that struck New Madrid, Missouri, and the 7.0 earthquake that struck Charleston, South Carolina, in the 1800s.