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What’s the difference between weather and climate?

Weather describes the current state of the atmosphere related to air temperature, humidity, pressure and wind.

We talk about climate when we talk about statistics of weather over long time scales (reference period of the World Meteorological Organization is 30 years). The statistics include average values, extremes, and variation.

Climate system has a wider definition. It includes statistics of the atmosphere, and all other components like the ocean, the cryosphere (glaciers, ice sheets, sea ice), the biosphere (vegetation, fauna and soil).

While 30 years is long enough to capture climatic variations in the atmosphere, other components of the climate system, like the deep ocean, take much more time to adjust to changes.

How is the weather monitored?

Besides permanent installations, additional stations are typically set up for shorter periods as part of field campaigns or seasonally on boats during the summer. Weather balloons are daily launched in Ny Ålesund and Bjørnøya to measure higher up in the atmosphere.

The harsh Arctic weather conditions themselves are challenging for the instruments. At the same time, maintenance of remote stations requires lots of resources, both in terms of manpower and equipment, such as snow scooters, boats or helicopters.

If something breaks, data might not be available for extended periods until the station can be fixed. Remote stations might not be reachable for most of the year. Also, quality control is challenging if there is no information on the state of a station for large parts of the year.

What characteristics define Arctic weather?

One of the most obvious answers is the polar day, and polar night, when the sun doesn’t’ set or rise above the horizon and how the vanishing of a diurnal cycle affects the surface heating and subsequently near-surface temperatures. In Svalbard both periods last for about four months each. 

Another characteristic is persistent katabatic winds, that carry air from higher elevation down a slope under a force of gravity. These occur e.g. over glaciers and in front of glaciers.

How does it differ from weather patterns in other regions?

Svalbard’s location is special. Laying between Fram Strait, with northward flowing warm Atlantic water in the West Spitsbergen Current, and the Arctic Ocean/northern Barents Sea with its colder Arctic-type water masses.

In addition, storm systems typically travel along what is called the North Atlantic Storm Track, transporting warm and moist air masses into the Svalbard region (potentially leading to positive temperatures even in the middle of winter). At the same time, northerly winds advect dry and cold air masses originating in the central Arctic

We also have potentially large temperature contrast between the water (not below -1.8^oC) and the air above (easily -20^oC during winter), which is leading to strong heat fluxes from the ocean to the atmosphere. However, sea ice cover is isolating the warm ocean below from the cold atmosphere, suppressing these air-sea heat fluxes.

These gradients imprint in climatologies of near-surface variables, e.g. west-east and south-north temperature (warm-cold) and precipitation (more – less) gradients.

Why is Arctic weather so unpredictable?

There are three major factors.

Firstly, numerical weather prediction (NWP) models need to discretize the world. To put it simply, putting a fishing net over the world and calculate variables like temperature and wind speed on each knot of that net. The finer the model grid is, the higher the resolution of the model. However, limitations in computational power set limits to the model resolution.

For current global forecasting models, the grid resolution is in the order of 10km. Regional models can have higher resolution, as they don’t cover the whole globe. Unfortunately, the topography varies substantially on the scale of 1km, and so NWP models cannot directly resolve flow in such complex terrain.

In addition, lots of important processes happen on scales smaller than the model grid, such as radiative transfer of both incoming solar radiation as well as thermal infrared radiation emitted by all terrestrial bodies, or processes related to the exchange of energy, momentum and mass between the atmosphere and the surface. These processes need to be parameterized and their effect on the local weather needs to be expressed using the variables calculated at the model grid points.

And the complex terrain in the Arctic, with a highly variably surface cover including glaciers, snow, sea ice and tundra, make it difficult to find good parameterizations, especially as it is challenging to obtain real life measurements of these processes.

Are there any phenomena unique to Svalbard that are surprising?

Yes, polar lows, known as “Arctic hurricanes”. They are really intense, but short-lived low-pressure systems forming when very cold air masses from the central Arctic move southwards over the sea ice edge over open water. Similarly to hurricanes in the tropics, the warm ocean surface (relative to the air above) supplies the energy needed to develop the polar low.

How are changes in global climate impacting the weather patterns?

A consequence of the Arctic Amplification is a reduced north-south temperature gradient between the Arctic and lower latitudes, leading to a more meandering jet stream. This, in turn, allows more north-south air mass exchange. This means that warm and moist air masses from lower latitudes are more often advected into the Arctic, leading to more variable weather patterns, including also more precipitation.

How do these patterns contribute to the weather outside polar regions?

The global circulation is in primarily driven by the uneven distribution of solar energy over the globe, with net heating in the low latitude near the equator and net cooling at the poles. A strong temperature gradient between the equator and the pole leads to stronger jet streams, which in turn isolate the high from the lower latitudes. These conditions favor warm and wet conditions in Northern Europe.

In turn, a weaker North-South temperature gradient allows for more meandering of the jet streams and subsequently more exchange of air masses between the Arctic and lower latitudes. Northern Europe typically experiences colder than average conditions during these periods. Climate indices like the “Arctic oscillation” quantify these changes in the global circulation.

How do weather patterns contribute to the weather outside polar regions?

The global circulation is in the first place driven by the uneven distribution of solar energy over the globe (net heating in the low latitude near the equator, net cooling at the poles). A strong temperature gradient between the equator and the pole leads to stronger zonal (west – east) winds (jet stream), which in turn isolates the high from the lower latitudes. These conditions, favor warm and wet conditions in Northern Europe.

In turn, a weaker North-South temperature gradient allows for more meandering of the jet streams and subsequently more exchange of air masses between the Arctic and lower latitudes (Northern Europe typically experiences colder than average conditions during these periods). Climate indices like the Arctic Oscillation (AO) quantify these changes in the global circulation.

Does sea ice influence Arctic weather or global climate systems?

Locally and regionally during winter, sea ice insulates the warm ocean from the cold atmosphere, which limits the heat flux from the ocean into the atmosphere and therefore also the near-surface atmospheric temperatures.

On a global scale, mainly during the summer, sea ice reflects a large portion of the incoming solar radiation compared to the darker ocean surface. This limits solar heating and contributes to making the Arctic a net energy sink, with more energy lost than gained, for the global climate system.

What knowledge gaps need to be addressed to predict changes?

The surface exchange processes that I mentioned earlier. Due to the challenging environmental conditions and limited accessibility compared to lower latitudes, it is challenging to obtain these measurements and hence parameterizations have larger uncertainties.

This is especially true for so-called stable boundary layers, conditions that typically occur during the polar night over snow- and ice-covered ground, when the surface cools dramatically, which in turn cools the lowest layers of the atmosphere. The cold air resting close to the bottom is heavier than the warmer air above, meaning that vertical motion including turbulence and exchange between these layers gets suppressed. Current NWP struggles with modelling these conditions.

And cloud physics. Clouds are in general a large uncertainty in climate models. While the formation of individual cloud particles takes place on very small scales, a cloud or cloud layer may easily cover several model grid cells.

However, depending on the microphysics, such as droplet size, water vs. ice, the macroscopic properties, “color”, which is related to the reflectance of solar radiation, largely vary. Improved parameterizations of cloud microphysics are required to adequately model their effect on the model grid variables.

Are there any discoveries that have intrigued you?

Progress in NWP has led to the first test runs with model grid resolutions of 500m. This pushes the boundaries of what can be resolved by the model.

Furthermore, new, innovative observing systems are being developed in addition to the “classical” weather stations. Several projects and institutions are working on new ways of obtaining measurements of parameters and from places that previously have been un-measurable or inaccessible.

For example, sensors are being installed on ships, drifters are set out on sea ice floes. Very high-resolution measurements of surface exchange processes are being made. The data obtained in this way gives a better understanding of small-scale processes, and improve results of the models we use, and serve as reference data for model experiments as well as satellite measurements.

What can we expect in the future?

The consensus is that the weather in Svalbard will be warmer, and even more variable. In addition, all models predict a wetter Arctic so we can expect much more rain in what used to be called a polar desert.

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Last update: 10. February 2025