Question

Q) What physical principles are used by radar to detect rain cloud? as well provide refernces for ur answer please

.NOTE : all below refernces are not allowed so do not get information from any of them ..

:( Wikipedia refrences ),

(National weather service(USA) www.weather.gov/jetstream / doppler),

National Meteorological library and Archive fact sheet 15. www.metoffice.gov.uk/binaries/content/assets/mohippo/pdf/r/radar and

Severe weather 101- tornadoes ,national severe storms laboratory /www.nssl.noaa.gov/education/svrwx101/tornadoes/detection

Answer 1

The main principle of radar is that it emits a beam of radiation into the atmosphere and records any radiation that comes back after reflecting from the objects in atmopshere.

Radars that are used for weather and clouds typically operate in microwave range i.e., the wavelength is of the order of few micro meters. This will get reflected from objects which are of sufficient sizes and the same radiation will pass smaller objects.

Objects capable of reflecting the radiation (microwave) are rain drops, snow flakes, birds, insects airplanes.

Clouds are nothing but a collection of large number of very small liquid drops or ice crystals. These cloud dropslets under certain circumstances will coalesce to form rain droplets. The size of rain droplets is considerably larger than the cloud droplets. These rain droplets are visible for radar. So cloud droplets are not visible to radar but the rain droplets are. So weather radars thus can detect these droplets in any clouds. But it is the rain droplets that the radar sees and naturally these droplets are present in the cloud. The most important aspect is that radar directly does not see any cloud but it only sees the rain droplets present in them.

you can refer to sfsu.edu website for radars and weather radars.