Improved Monitoring in Specific Synoptic Situations by LSA SAF LST
A case of temperature inversion in complex terrain
In winter cold-air pools in the lowest layers of the atmosphere are frequently formed due to night-time cooling. This can result in significant temperature inversion in valleys and basins. A typical weather situation with a pronounced temperature inversion developed in late December over Slovenia. Temperature inversion formed only over deeper basins and some valleys with maximum temperatures at around 1500 metres above sea level. Above valley and basin floors moderate west winds caused the mixing of the atmosphere which resulted in higher temperatures.
LSA SAF land surface temperature (LST) instantaneous image from EUMETSAT‘s geostationary MSG satellite (left figure) and analysis performed by Slovenian Meteorological Nowcasting System (MetNS, right figure) were compared with in-situ temperature measurements for 25 December 2017 04 UTC. Additionally, the MetNS figure displays which in-situ air temperature measurements at 5 cm were assimilated in the model (shown as black dots). The comparison revealed what benefits LST can offer in the scope of nowcasting when used together with a nowcasting system:
- Satellite image is clearly beneficial in areas with a lower density of in-situ measurement sites, particularly in the mountainous regions.
- In snow-covered areas satellite LST has an advantage at evaluating land surface temperature as the model relies on the air temperature to estimate land surface temperature.
- Finally, LST is useful for identification of local weather characteristics that are not represented in the model when in-situ measurements are located on the edge of the local-scale weather pattern. On this particular day these weather patterns had a crucial impact on the development of the local temperature inversion, which in turn is very important for a correct assessment of areas with a risk of icy roads.
In these specific situations LSA SAF LST is of great help for nowcasters when data are available (only in cloud-free situations). In this sense, satellite LST complements nowcasting products which are available at all times in cloud-free and cloudy situations. For custom-tailored products, e.g., identification of icy roads at temperatures around freezing point the LST product has a potential to be useful in assessing road safety. More on the LST product