9:15 AM - 9:30 AM
[ACG39-02] Seasonal and long-term variations in the top of the atmosphere shortwave radiation over the Arctic
Keywords:shortwave radiation, sea ice, snow cover, cloud
The Arctic region has recently experienced significant climate changes such as a decrease in sea ice extent and a decrease in snow cover. Sea ice and snow cover have high albedo, and these changes significantly impact shortwave radiation. Cloud is also essential in the variability of shortwave radiation. Therefore, it is necessary to quantitatively evaluate the effects of clouds, sea ice, and snow cover.
The recent decrease in sea ice extent has been linked to a decrease in the upward shortwave radiation at the top of the atmosphere over the Arctic ocean (Hartmann and Ceppi, 2014; Pistone et al., 2014). Besides, cloud variability on shortwave radiation variation is negligible (Pistone et al., 2014). Most of these previous studies have focused on annual mean or summer to analyze the long-term variation in shortwave radiation. However, the seasonal variability of sea ice and snow cover in the Arctic is large. It is necessary to evaluate the long-term variation in shortwave radiation in each season. This study analyzes the long-term variation in shortwave radiation in each season from 2001 to 2019 using satellite observation data.
The upward shortwave radiation had been a downward trend over the entire Arctic region from 2001 to 2012, and the sizeable inter-annual variability after 2012. The variability is different for land and ocean. Over the ocean, the upward shortwave radiation decreased from 2001 to 2007, and sizeable inter-annual variability after 2007. It relates to an increase in the sea ice variability after 2007. The sea ice extent decreased sharply in 2007. In March 2008, there was a sharp increase in the one-year ice fraction (Richer-Menge and Druckenmiller, 2020). Thus, it seems to cause an increase in sea ice variability. The shortwave cloud radiative effect increased after 2007, and it weakens the decline in shortwave radiation. Over the land, it seems to be attributed to the increase in the snow cover extent's inter-annual variability after 2012.
Seasonal variability is different between land and ocean. Sea ice extent is maximum in March and minimum in September. Snow cover extent is maximum in February and minimum in August. The upward shortwave radiation is maximum in June over the ocean and in May over the land. Besides, since the variability of sea ice, snow cover, and cloud is different each month, the months with the largest variations in upward shortwave radiation also vary from year to year. Therefore, it is necessary to pay attention to seasonal changes in sea ice, snow cover, and clouds to understand the long-term variation in shortwave radiation.
The recent decrease in sea ice extent has been linked to a decrease in the upward shortwave radiation at the top of the atmosphere over the Arctic ocean (Hartmann and Ceppi, 2014; Pistone et al., 2014). Besides, cloud variability on shortwave radiation variation is negligible (Pistone et al., 2014). Most of these previous studies have focused on annual mean or summer to analyze the long-term variation in shortwave radiation. However, the seasonal variability of sea ice and snow cover in the Arctic is large. It is necessary to evaluate the long-term variation in shortwave radiation in each season. This study analyzes the long-term variation in shortwave radiation in each season from 2001 to 2019 using satellite observation data.
The upward shortwave radiation had been a downward trend over the entire Arctic region from 2001 to 2012, and the sizeable inter-annual variability after 2012. The variability is different for land and ocean. Over the ocean, the upward shortwave radiation decreased from 2001 to 2007, and sizeable inter-annual variability after 2007. It relates to an increase in the sea ice variability after 2007. The sea ice extent decreased sharply in 2007. In March 2008, there was a sharp increase in the one-year ice fraction (Richer-Menge and Druckenmiller, 2020). Thus, it seems to cause an increase in sea ice variability. The shortwave cloud radiative effect increased after 2007, and it weakens the decline in shortwave radiation. Over the land, it seems to be attributed to the increase in the snow cover extent's inter-annual variability after 2012.
Seasonal variability is different between land and ocean. Sea ice extent is maximum in March and minimum in September. Snow cover extent is maximum in February and minimum in August. The upward shortwave radiation is maximum in June over the ocean and in May over the land. Besides, since the variability of sea ice, snow cover, and cloud is different each month, the months with the largest variations in upward shortwave radiation also vary from year to year. Therefore, it is necessary to pay attention to seasonal changes in sea ice, snow cover, and clouds to understand the long-term variation in shortwave radiation.