5:15 PM - 7:15 PM
[MIS05-P01] Cold and shoulder season freezing rain events: Climatology, tendencies, and weather conditions favorable to these events
Keywords:Northern Eurasia, freezing rain, climatology, conditions favorable to freezing rain
Freezing rainfall processes are related to the CLIMATE EXTREMES WCRP Grand Challenge. Freezing precipitation causes significant socio-economic impacts, and there are ongoing challenges related to its detection, variation, comprehension, and forecasting.
To understand future changes in hazardous cold/shoulder season freezing rain events, we need to document freezing rain climatology, to quantify weather conditions that are conducive to freezing rainfall, and to try projecting these conditions into the future. For the first goal, we collected hourly/3-hourly data from 1,500 synoptic stations in the northern extratropics for the past fifty years ( Groisman et al. 2015, 2016, 2018). For the second goal, we employed data of collocated synoptic and aerologic stations, as well as the reanalyses output. This information allowed us to define weather conditions that are conducive to freezing rainfall at the synoptic stations and, thereafter, expand this definition across the northern extratropics below 1,200 meters a.s.l. The generalized definition of weather conditions conducive to freezing rain during precipitation. Under this definition, several weather events must occur simultaneously: (a) precipitation at the surface must be above zero, (b) surface air temperature should be in the range between -5.0°C and 0.2°C, and (c, d) the air temperature at 850 hPa and 700 hPa levels should be above -0.4° and -6° respectively. The last two requirements approximate our assumption of the presence of warm front above the spot of the freezing rain event (Figure 1). The elevation restriction is due to the inclusion into the above formulas the air temperature at 850 hPa. The 850 hPa layer may well be below the surface elevation in the mountainous terrain. As a result, the air temperature at this layer is not an accurate indicator of the temperature above the surface. This temperature usually describes inversions happening when warm air moves between cold air near the surface and snowy clouds. Nevertheless, even such coarse approximation allowed us to identify from 60 to 70 percent of freezing events over synoptic stations in our analysis. We had at hand the NCEP Climate Forecast System Reanalysis V2, CFSRv2 information (Suraniana et al. 2014). Using it, we estimated the time series of weather conditions conducive to freezing rain in the northern extratropics below 1,200 meters a.s.l. Our presentation will cover their climatology and dynamics. We will also examine the changes in the frequency and geographical distribution of these events.
References:
Groisman, P..Y., O. N. Bulygina, X. Yin, R. S. Vose, S. K. Gulev, I. Hanssen-Bauer, and E. Førland 2016: Recent changes in the frequency of freezing precipitation in North America and Northern Eurasia. Environ. Res. Lett. 11, 045007.
Groisman P Y, Zolina O G, Gulev S K, Hanssen-Bauer I, Førland E, Bulygina O N, Yin X and Vose R 2015 Cold/shoulder season precipitation near 0 °C Int. Conf. ‘Our Common Future under Climate Change(Paris France, 7–10 July 2015) abstract book P-1109-03 86-87.
Groisman P. Y., X. Yin, O. N. Bulygina, and I.S. Danilovich. Human-Associated Extreme Events: Freezing Precipitation. Poster presented at Annual JpGU Meeting, 20-25 May. 2018, Makuhari, Chiba, Japan.
Suraniana, S. et al. 2014: The NCEP Climate Forecast System Version 2 Journal of Climate J. Climate, 27, 2185–2208. doi: http://dx.doi.org/10.1175/JCLI-D-12-00823.1
To understand future changes in hazardous cold/shoulder season freezing rain events, we need to document freezing rain climatology, to quantify weather conditions that are conducive to freezing rainfall, and to try projecting these conditions into the future. For the first goal, we collected hourly/3-hourly data from 1,500 synoptic stations in the northern extratropics for the past fifty years ( Groisman et al. 2015, 2016, 2018). For the second goal, we employed data of collocated synoptic and aerologic stations, as well as the reanalyses output. This information allowed us to define weather conditions that are conducive to freezing rainfall at the synoptic stations and, thereafter, expand this definition across the northern extratropics below 1,200 meters a.s.l. The generalized definition of weather conditions conducive to freezing rain during precipitation. Under this definition, several weather events must occur simultaneously: (a) precipitation at the surface must be above zero, (b) surface air temperature should be in the range between -5.0°C and 0.2°C, and (c, d) the air temperature at 850 hPa and 700 hPa levels should be above -0.4° and -6° respectively. The last two requirements approximate our assumption of the presence of warm front above the spot of the freezing rain event (Figure 1). The elevation restriction is due to the inclusion into the above formulas the air temperature at 850 hPa. The 850 hPa layer may well be below the surface elevation in the mountainous terrain. As a result, the air temperature at this layer is not an accurate indicator of the temperature above the surface. This temperature usually describes inversions happening when warm air moves between cold air near the surface and snowy clouds. Nevertheless, even such coarse approximation allowed us to identify from 60 to 70 percent of freezing events over synoptic stations in our analysis. We had at hand the NCEP Climate Forecast System Reanalysis V2, CFSRv2 information (Suraniana et al. 2014). Using it, we estimated the time series of weather conditions conducive to freezing rain in the northern extratropics below 1,200 meters a.s.l. Our presentation will cover their climatology and dynamics. We will also examine the changes in the frequency and geographical distribution of these events.
References:
Groisman, P..Y., O. N. Bulygina, X. Yin, R. S. Vose, S. K. Gulev, I. Hanssen-Bauer, and E. Førland 2016: Recent changes in the frequency of freezing precipitation in North America and Northern Eurasia. Environ. Res. Lett. 11, 045007.
Groisman P Y, Zolina O G, Gulev S K, Hanssen-Bauer I, Førland E, Bulygina O N, Yin X and Vose R 2015 Cold/shoulder season precipitation near 0 °C Int. Conf. ‘Our Common Future under Climate Change(Paris France, 7–10 July 2015) abstract book P-1109-03 86-87.
Groisman P. Y., X. Yin, O. N. Bulygina, and I.S. Danilovich. Human-Associated Extreme Events: Freezing Precipitation. Poster presented at Annual JpGU Meeting, 20-25 May. 2018, Makuhari, Chiba, Japan.
Suraniana, S. et al. 2014: The NCEP Climate Forecast System Version 2 Journal of Climate J. Climate, 27, 2185–2208. doi: http://dx.doi.org/10.1175/JCLI-D-12-00823.1