“Radio waves do not travel through a vacuum of certainty. They move through an atmosphere that is restless, layered, and full of weather, and in that atmosphere their fate is decided.” – John D. Kraus, Antennas
Introduction
Radio frequency (RF) propagation is the study of how electromagnetic waves travel through the atmosphere and other media. The performance of radio systems in communications, navigation, radar, and measurement applications depends heavily on how signals propagate from transmitter to receiver. A fundamental question that engineers, scientists, and regulators must address is whether RF propagation changes with the weather. The answer is unequivocally yes, though the mechanisms and degree of impact vary with frequency bands, atmospheric composition, and the specific weather phenomena present at any given time.
Fundamental Principles of RF Propagation
Electromagnetic waves travel through free space at the speed of light, with predictable losses due to spreading and absorption. However, the Earth is not a vacuum. The atmosphere is composed of gases, water vapour, suspended particles, and varying temperature layers, each of which alters the path, attenuation, and reliability of RF signals. The dielectric properties of the atmosphere change as temperature, humidity, and pressure fluctuate, which means that radio signals interact differently depending on the prevailing meteorological conditions.
At lower frequencies, such as those below 30 MHz, propagation is influenced more by ionospheric conditions than by weather systems in the troposphere. Conversely, at higher frequencies in the microwave and millimetre-wave range, atmospheric weather events such as rain, fog, and snow dominate attenuation. For mid-range frequencies used in cellular networks, Wi-Fi, and municipal advanced metering infrastructure (AMI), a mix of both factors can influence performance.
Temperature and Humidity Effects
Temperature gradients in the atmosphere cause refractive bending of RF signals. When warm air overlays cooler air near the surface, an inversion layer forms. This creates ducting conditions in which radio signals can travel further than normal, sometimes hundreds of kilometres beyond the radio horizon. While this may temporarily improve long-distance communications, it also introduces interference between systems operating on the same frequencies in different regions.
Humidity has a direct relationship with absorption of radio energy, particularly at frequencies near the water vapour resonance lines around 22 GHz and 183 GHz. In practical terms, microwave links that perform well under dry conditions may exhibit severe degradation during periods of high humidity. The attenuation is not linear; it rises sharply as water vapour density increases, making tropical and coastal climates particularly challenging for systems operating in these frequency ranges.
Rain and Precipitation
Rain is one of the most significant weather-related factors influencing RF propagation. Raindrops scatter and absorb radio waves, an effect most pronounced at frequencies above 10 GHz. The severity depends on rainfall rate, drop size distribution, and polarization of the signal. For satellite communications and backhaul microwave links, heavy rain events can result in fade margins exceeding 20 dB, enough to cause complete signal loss if systems are not engineered with adequate link budgets.
Snow and hail also contribute to attenuation, although the impact is somewhat less severe than rain due to lower water content. However, wet snow can cling to antennas and radomes, physically de-tuning them and further increasing signal degradation. Freezing rain can create an ice layer on transmission infrastructure, altering the electrical characteristics of antenna surfaces. These effects are of critical importance in northern climates such as Canada, where winter precipitation is frequent and persistent.
Fog and Clouds
Fog is composed of tiny suspended water droplets, typically less than 100 micrometres in diameter. Despite their small size, they can cause scattering losses at millimetre-wave frequencies. At 60 GHz, commonly considered for short-range wireless links, attenuation due to fog can be several dB per kilometre, enough to render longer links unreliable. Clouds at higher altitudes have similar effects, especially for earth-to-satellite paths where signals must traverse thick cloud layers. This is a significant factor for satellite Earth observation and Ka-band satellite Internet services, which must implement adaptive coding and power control to mitigate weather-induced losses.
Wind and Storms
Wind by itself has little direct effect on radio propagation. Its role is primarily indirect, through the movement of particulate matter, dust, and water vapour. Strong winds can alter temperature stratification in the atmosphere, which modifies refractive conditions. Severe storms, such as thunderstorms, produce rapid fluctuations in refractivity, leading to scintillation of signals, which is observed as rapid amplitude and phase variations. Lightning generates impulsive broadband noise, which can overwhelm receivers at low and medium frequencies.
Atmospheric Pressure and Tropospheric Refraction
Atmospheric pressure affects the density of air, and therefore the refractive index. Higher pressure leads to denser air, which causes signals to bend more as they travel across long distances. This effect is subtle, but it can influence the reliability of long-range terrestrial links. The troposphere, extending up to about 12 kilometres, is the layer where weather phenomena occur and where most RF systems operate. Small variations in refractive index within the troposphere lead to multipath fading, ducting, and anomalous propagation events.
“The atmosphere is the most variable transmission line ever built, and weather is the engineer of its changes.” – Edward J. King, Radio Propagation Fundamentals
Frequency Dependence of Weather Impacts
The sensitivity of RF propagation to weather is strongly frequency dependent.
- Below 30 MHz: Dominated by ionospheric effects, with little direct impact from local weather.
- 30 MHz to 3 GHz: Weather effects are modest, though heavy rain and humidity can still introduce measurable losses in UHF and L-band systems used for television broadcasting, cellular services, and navigation.
- 3 GHz to 30 GHz: Weather effects become pronounced. Rain attenuation is a dominant factor in C-band, Ku-band, and Ka-band satellite services. Fog, humidity, and clouds add further losses.
- Above 30 GHz: The millimetre-wave region is highly sensitive to weather, with absorption peaks at oxygen resonance near 60 GHz and water vapour resonance near 183 GHz. These bands are considered short-range or specialized due to extreme susceptibility to atmospheric absorption and precipitation.
Engineering Mitigation Strategies
Engineers must design RF systems to withstand the variable effects of weather. This is achieved through fade margin allocation, antenna diversity, adaptive modulation, and dynamic power control. In satellite systems, link adaptation techniques that adjust coding and modulation schemes in real time are used to compensate for rain fade. Ground-based networks often employ site diversity, where multiple paths are maintained and the best link is dynamically selected based on current conditions.
For municipal metering and telemetry systems, frequencies are usually chosen in the sub-GHz range where weather impacts are less severe. Even so, heavy snowfall, freezing rain, and rapid temperature changes in Canadian environments can still cause temporary impairments, which must be accounted for in system design.
Canadian Context
Canada presents a unique challenge for RF propagation studies due to its vast geography and climatic diversity. In coastal regions such as British Columbia, high humidity and frequent rain make microwave link design particularly challenging. In the Prairies, temperature inversions during winter often lead to anomalous propagation and unexpected interference between long-distance links. An interesting associated effect in the Prairies occurs when rainfall remains on the ground surface when the land cannot absorb it. The water acts like a mirror and reflects microwave signals resulting in misalignment, multipath, and loss of signals. In northern territories, snow and ice accumulation on antennas present practical problems for long-term system reliability.
Measurement campaigns conducted by Canadian universities and regulatory agencies have repeatedly shown that weather-related impairments cannot be ignored in system planning. For example, rain fade statistics collected in Vancouver differ significantly from those in Calgary, Toronto, and Montreal underscoring the need for region-specific engineering data rather than generalized models. Rainfall in Vancouver is more of a constant misty rain, similar to the mist off of Niagara Falls, whereas in other urban centres listed above it is dense cell, combined with raging winds, and thunder and lightning. It pours down in fierce torrential storms lasting just 10 to 30 minutes. These storms have been measured at 20 dB to 40 dB attenuation. Most microwave and satellite links are designed with about 6 dB to 10 dB of overhead margin. So temporary system outages result.
Summary
Radio frequency propagation is intrinsically influenced by weather conditions. The atmosphere is not static; it is a dynamic medium where temperature, humidity, precipitation, and pressure constantly change. Each of these factors alters the refractive, absorptive, and scattering properties of the medium, thereby affecting how RF signals propagate. The degree of influence depends on frequency, geography, and climate, making weather-aware engineering essential for reliable communication systems.
In the Canadian context, engineers must address a wide spectrum of weather events ranging from heavy rain on the west coast to freezing precipitation in the east and Arctic extremes in the north. Effective system design requires both theoretical understanding and empirical measurement of weather impacts. As society increasingly depends on wireless communications, the interaction between RF propagation and weather will remain a central challenge for engineers and researchers.
About the Author:
Michael Martin is the Vice President of Technology with Metercor Inc., a Smart Meter, IoT, and Smart City systems integrator based in Canada. He has more than 40 years of experience in systems design for applications that use broadband networks, optical fibre, wireless, and digital communications technologies. He is a business and technology consultant. He was a senior executive consultant for 15 years with IBM, where he worked in the GBS Global Center of Competency for Energy and Utilities and the GTS Global Center of Excellence for Energy and Utilities. He is a founding partner and President of MICAN Communications and before that was President of Comlink Systems Limited and Ensat Broadcast Services, Inc., both divisions of Cygnal Technologies Corporation (CYN: TSX).
Martin served on the Board of Directors for TeraGo Inc (TGO: TSX) and on the Board of Directors for Avante Logixx Inc. (XX: TSX.V). He has served as a Member, SCC ISO-IEC JTC 1/SC-41 – Internet of Things and related technologies, ISO – International Organization for Standardization, and as a member of the NIST SP 500-325 Fog Computing Conceptual Model, National Institute of Standards and Technology. He served on the Board of Governors of the University of Ontario Institute of Technology (UOIT) [now Ontario Tech University] and on the Board of Advisers of five different Colleges in Ontario – Centennial College, Humber College, George Brown College, Durham College, Ryerson Polytechnic University [now Toronto Metropolitan University]. For 16 years he served on the Board of the Society of Motion Picture and Television Engineers (SMPTE), Toronto Section.
He holds three master’s degrees, in business (MBA), communication (MA), and education (MEd). As well, he has three undergraduate diplomas and seven certifications in business, computer programming, internetworking, project management, media, photography, and communication technology. He has completed over 60 next generation MOOC (Massive Open Online Courses) continuous education in a wide variety of topics, including: Economics, Python Programming, Internet of Things, Cloud, Artificial Intelligence and Cognitive systems, Blockchain, Agile, Big Data, Design Thinking, Security, Indigenous Canada awareness, and more.