Why did an air defense alert sound in Hangzhou on September 8, 2011?

Xinhuanet Henan Channel reported on September 17, Dahe Net-Henan Daily reported: (Reporter Wen Xiaojuan) The reporter learned from the Provincial Civil Defense Office that September 17 is the 11th National Defense Education Day, and also the Henan National Defense Education Day. Provincial Civil Defense Alarm Sounding Day. From 9:30 to 10:30 on the morning of the 17th, 18 key civil defense cities in the province and the counties and cities under their jurisdiction will sound air defense and disaster prevention sirens. Citizens should not panic after hearing the sirens. The person in charge of the Provincial Civil Defense Office said that the province-wide air defense siren is a trial in non-emergency conditions. It is mainly to enhance the citizens’ concept of national defense and civil defense awareness and ensure that they can quickly evacuate and hide during wartime and emergencies. .