A weather radar that measures both precipitation location and the speed of raindrops, revealing storm structure, rotation and downbursts. Backbone of modern monsoon forecasting.
forecastingWhat is Doppler Radar?
A Doppler weather radar is a specialized radar system designed to detect precipitation and measure how fast it is moving toward or away from the radar. It emits microwave pulses (typically S-band 2-4 GHz or C-band 4-8 GHz) and receives returned echoes from raindrops, hailstones, snowflakes, ice crystals — and the air itself if dense enough.
Two measurements are recorded for each returned echo:
- Reflectivity (dBZ) — how strong the echo is, which translates to precipitation intensity.
- Radial velocity (m/s) — the speed of the precipitation toward or away from the radar (the Doppler shift).
This combination reveals not just where rain is falling but how the air is moving inside the storm — critical information for identifying cyclone eyes, severe thunderstorm rotation, downbursts, gust fronts, and convergence patterns.
For South Asia, Doppler radar is the single most important nowcasting tool. The IMD operates a network of 38+ Doppler radars with new installations planned under the Mission Mausam programme (2024-2030).
How Doppler radar works
The radar antenna rotates 360° every few minutes, scanning a circular area with a radius of typically 200-400 km. For each direction, it transmits a pulse and listens for echoes returning from precipitation. The Doppler effect — frequency shift of the returned wave — tells the radar the radial velocity of the drops:
- Negative velocity = drops moving TOWARD the radar
- Positive velocity = drops moving AWAY from the radar
- Zero velocity = drops moving perpendicular to the radar beam
By combining reflectivity and velocity data from multiple scan angles (elevation), the radar builds a 3D model of precipitation and winds within its range.
Doppler radar deployment in South Asia
India (IMD): The IMD operates 38+ Doppler Weather Radars (DWR) across the country. Major installations:
- Delhi (Mausam Bhawan, Lodi Road) — covers NCR and adjoining UP/Haryana/Rajasthan
- Mumbai (Veravali, Western Ghats) — Konkan coast monitoring
- Kolkata (Mohanpur) — Bay of Bengal cyclone tracking
- Chennai (Pallikaranai) — Tamil Nadu cyclones, NEM monitoring
- Visakhapatnam, Bhubaneswar — east coast cyclone tracking
- Patna, Lucknow — Indo-Gangetic monsoon depressions
- Hyderabad, Bangalore — peninsular India
- Ahmedabad, Bhuj — Arabian Sea cyclone monitoring
- Goa, Karaikal, Machilipatnam — coastal monitoring
Pakistan (PMD):
- Karachi DWR (Saddar) — Arabian Sea, Sindh coast
- Lahore DWR — Punjab plains
- Islamabad DWR — Pothwar/KP region
- Sialkot DWR (newer)
- Multan DWR (planned)
Bangladesh (BMD):
- Cox’s Bazar DWR — cyclone tracking
- Dhaka DWR — Bangladesh interior
- Khepupara DWR — coastal
- Rangpur DWR — north
Sri Lanka (DoM):
- Colombo, Anuradhapura DWR
Nepal (DHM):
- Chitwan DWR
Capabilities and use cases
Tropical cyclone tracking:
- Once a cyclone enters DWR range (200-400 km), the eye, eyewall and rainbands are clearly visible
- Track and intensity estimates update every 10 minutes
- Storm surge predictions refined by detailed wind data
- Recent example: Cyclone Michaung (Dec 2023) — Chennai DWR tracked it 36 hours before landfall
Monsoon depression monitoring:
- Even non-named depressions tracked
- Heavy rainfall potential assessed in real time
- Critical for Bihar, Bengal, Odisha flood warnings
Severe thunderstorm nowcasting:
- Pre-monsoon Nor’westers (Kal Baisakhi) identified 30-60 min before impact
- Hail-producing storms distinguished from rain-only
- Tornado-spawning supercells flagged
Aviation:
- Pilots avoid Doppler-detected severe weather cells
- Airports use radar for landing/takeoff decisions
- Wind shear advisories from velocity data
Hydrology:
- Real-time rainfall estimates feed flood models
- Catchment-scale rainfall aggregated for reservoir management
- River flow forecasts use radar data
Dual-polarization Doppler
Modern Doppler radars (post-2010) transmit pulses with both horizontal and vertical polarization. The ratio of returned echoes from each polarization reveals:
- Drop shape — large raindrops are oblate (squashed), small ones round
- Hydrometeor type — distinguishes rain from hail, snow, mixed precip
- Particle size distribution — improves rainfall estimates
- Debris signature — tornadoes can be confirmed by debris signatures
The IMD’s newer DWRs (Patna 2017, Mohanpur 2020, others) have dual-polarization. This significantly improves cyclone and thunderstorm detection.
Nowcasting on Mausam Online
While Mausam Online doesn’t display raw radar imagery (which requires specialized rendering), our forecasts incorporate radar-derived information through Open-Meteo’s ECMWF integration. For acute severe-weather monitoring, residents should also check:
- IMD Sachet app — official severe weather alerts based on radar nowcasting
- IMD’s MOSDAC website — real-time radar imagery
- PMD’s CDF — Pakistan’s radar composite
- BMD’s Weather Map — Bangladesh radar
For your city’s hourly precipitation forecast, see Delhi, Mumbai, Chennai, Kolkata, Dhaka, Karachi.
Frequently asked questions
How far can a Doppler radar see? Typical operational range is 200-400 km from the radar site. Beyond that, the Earth’s curvature places precipitation above the radar beam. Strong storms within 100 km are seen with greatest detail.
Why does my weather app not show radar? Most weather apps focus on model-based forecasts (more useful for multi-day planning) rather than radar nowcasting (useful for next 1-2 hours). Both are valuable; check IMD’s dedicated radar pages for nowcasting.
Are there gaps in radar coverage in India? Yes — northeastern states, parts of central India, and remote Himalayan regions have limited DWR coverage. The Mission Mausam programme (2024-2030) aims to add 25+ new radars to close gaps.
Can Doppler radar predict tornadoes? It can identify supercell thunderstorms with rotation signatures (“mesocyclones”) that are pre-cursors to tornadoes. With dual-polarization, actual tornado debris can be detected. Bangladesh’s tornado-prone Nor’wester regions are increasingly monitored.
Where can I see Doppler radar imagery for my city? IMD’s MOSDAC website (mosdac.gov.in) provides public radar imagery for major Indian cities. Updates every 10 minutes. Mausam Online focuses on forecasts rather than raw imagery.