23 May 2022 16:00 - 16:45
MAQ Colloquium announcement
Speaker: Malva Laurelin (MSc thesis)
"Quantifying Changes in Moisture Sources and Carbon Uptake During the 2018 Summer Drought in Scandinavia"
"In the summer of 2018 Europe was hit by a severe drought where also the high- latitude ecosystems of Scandinavia, which rarely experience such extreme weather events, were affected. Here, we use an interdisciplinary approach to study how the drought propagated through the atmosphere and the soil before influencing the carbon uptake in Southern Scandinavia. We assess the atmospheric moisture sources, soil moisture and photosynthetic capacity for the summer period May- August (MJJA) 2018 in comparison to the year prior, 2017. For this, we use mul- tiple models and remote sensing datasets, including the Eulerian moisture tracking model WAM-2layers, the hydrological model PCR-GLOBWB, the biosphere model SiB4 as well as soil moisture satellite data from VanderSat and vegetative remote sensing from NIRV.
While the 2018 high-pressure system over Scandinavia blocked moisture advection into the region, moisture from Eastern European sources was promoted and regional moisture recycling increased (6-8%) compared to the reference year. Although the meteorological drought prevailed during the summer and soil moisture decreased, it remained readily available throughout the whole period. We did not find any signif- icant differences in soil moisture for the regions three most common plant functional types (PFTs): evergreen needleleaf forest (ENF), deciduous broadleaf forest (DBF) and C3 crops (C33). The drought did not lead to a depletion in soil moisture, and photosynthesis was not water-limited. Instead, the drought onset in May 2018 cre- ated beneficial conditions for plant growth, and the high soil moisture storage at the beginning of the period together with the increased temperatures and incoming radiation led to an early activation of vegetation and enhanced photosynthesis. This ’spring boost’, where gross primary productivity (GPP) increased and net ecosystem exchange (NEE) decreased, resulted in a larger carbon uptake than the reference year. Although soil moisture was not a limiting factor, the carbon uptake decreased in July and August 2018. Instead, we found that the decreasing photosynthesis was a consequence of other plant stress factors such as decreasing humidity, enhanced vapor pressure deficit (VPD) and high temperatures."
Supervisor: Wouter Peters
23 May 2022 16:45-17:30
MAQ Colloquium announcement
Speaker: Glenn Graafeiland (MSc thesis)
Title: Arctic Micro-and Boundary Layer Meteorology Observed during MOSAiC Campaign.
Abstract: Warming of the Artic results in a rapid decrease of Arctic sea ice, whose rate is hard to quantify. To shed light on the energy exchange between the lower atmosphere and the snow- or ice-covered surface, the surface albedo, cloud cover, and surface roughness in the central Arctic were studied by means of a full year of meteorological observations gathered during the MOSAiC campaign (2019/2020). The surface albedo shows variation on a seasonal scale, on a scale from days-weeks, and diurnal variations were observed. The average surface albedo in early spring is 0.81 and drops throughout summer to and average value of 0.6 in July. Daily to weekly variations in surface albedo were linked to cloud cover. In April-May, the surface albedo positively correlates with cloud cover (R^2 = 0.72), while in June-July this correlation is very weak (R2 = 0.17). Daily variations were analyzed for clear sky conditions in April and June. In April, the albedo rapidly increases as the solar zenith angle (SZA) decreases, while in June the albedo slowly drops as the SZA increases. Moreover, the maximum and minimum albedo are reached at different times during the day. Surface albedo measurements indicate the presence of snow-covered surface in April and May and an ice-covered surface in June-July. Winter showed less cloud coverage on average, but clouds were more persistent. In summer, cloudy and clear periods are shorter but mean monthly values are higher. The influence of clouds on the surface temperature is variable over the seasons. Clouds warm the surface in winter and to a lesser extent also in spring, but in summer, the temperature remains relatively constant during transitions from cloudy to clear skies. In November, low temperatures are observed, ranging between -33 ◦C and -16 ◦C, largely influenced the incoming LW radiation. In April, the temperature is -2 ◦C under a fully clouded sky and remains around -19◦C during a cloudless period of 3 days. In June, the temperature is around 0 ◦C, whether it is cloudy or not. Overall mean z0m values in the order of 10^−4(m) are inferred, with March, April and June showing elevated values which are in the order of 10^−3(m). Inferred (z0T ) values range from from 10^−5(m) and 100(m), showing a large scatter over the year. January, March, and April 2020 show a relatively large z0m when winds are in northwesterly direction. This could be the effect of a storm event, which can result in the buildup of snow ridges perpendicular to the wind direction. Ratios of z0T /z0m were found on average to be 3-4 orders of magnitude higher than in previous research. Despite some limitations, data by MOSAiC expedition enabled this research to make the first steps in a more accurate understanding of Arctic radiationregimes.
Supervisor: Gert-Jan Steeneveld & Laurens Ganzeveld
26 April 2022 16:00-16:45
MAQ Colloquium announcement
Speaker: Ryan Sondij
Supervisor: Laurens Ganzeveld