New artworks by the contemporary Chinese-born artist Cai Guo-Qiang are now being exhibited on the Cantor Roof Garden at New York’s Metropolitan Museum of Art . “Clear Sky Black Cloud,” three explosions each releasing a dark smoke-cloud, will appear over Central Park six days a week at noon for the next six months. Given the ongoing U.S. occupation of Iraq, these firepower black clouds look ominously like anti-aircraft flak, especially when accompanied by shots loud as thunder. Still, they evoke springtime’s sublime kiss of bliss when they evanesce, enhancing heaven’s unblemished tranquility.