Higher Temperatures Have Contrasting Effects on Different Components of Forage Quality for Caribou in Northern Alaska

Rising temperatures in the Arctic may affect vegetation, which in turn can affect herbivores, such as caribou, that rely on these plants for forage. Several plant traits contribute to forage quality, including digestibility, nitrogen content, and antiherbivory secondary compounds, but the effect of temperature on these traits individually and combined is unclear. I conducted a three-component study on the effect of higher temperatures on the forage quality of graminoids, deciduous shrubs, and evergreen dwarf shrubs on the North Slope of Alaska. The components included: 1) short and long-term experimental warming, 2) natural temperature variation between south and north-facing slopes, and 3) natural temperature variation along a latitudinal gradient. Metrics measured were dry matter digestibility (DMD), leaf nitrogen concentration (N), and protein-precipitating capacity (PPC) of plant secondary compounds. Leaf N and PPC were integrated to calculate digestible protein (DP) available to caribou. In the warming experiment, DMD in June was higher while DP was lower under short-term warming compared to other treatments in Betula nana and Salix pulchra (deciduous shrubs). Conversely, Eriophorum vaginatum (graminoid) experienced lower DMD but higher leaf N in June under short-term warming. These contrasting metric responses suggest that higher temperatures may mitigate overall effects on forage quality early in the growing season. There was no difference in E. vaginatum DMD or N in either long-term warming plots compared to ambient plots, suggesting long-term acclimation to higher temperatures. In deciduous shrubs, DP was higher in July under long-term warming compared to other treatments, and on south-facing slopes compared to north-facing slopes in July 2019, indicating that many summers of warming may improve deciduous shrub forage quality in late summer. However, different responses in the slope aspect study between 2018 and 2019 may reflect differences in winter snow rather than summer temperature. In the latitudinal temperature gradient study, leaf N varied greatly among species, and no patterns were detected. Overall, responses differed among species and between summer months. Deciduous shrubs, which are preferred by caribou, are becoming increasingly abundant and may experience improved forage quality in late summer under long-term warming, which will further benefit caribou

Storms and the Depletion of Ammonia in Jupiter: I. Microphysics of “Mushballs”

Microwave observations by the Juno spacecraft have shown that, contrary to expectations, the concentration of ammonia is still variable down to pressures of tens of bars in Jupiter. We show that during strong storms able to loft water ice into a region located at pressures between 1.1 and 1.5 bar and temperatures between 173 and 188 K, ammonia vapor can dissolve into water ice to form a low‐temperature liquid phase containing about one‐third ammonia and two‐third water. We estimate that, following the process creating hailstorms on Earth, this liquid phase enhances the growth of hail‐like particles that we call mushballs. We develop a simple model to estimate the growth of these mushballs, their fall into Jupiter’s deep atmosphere, and their evaporation. We show that they evaporate deeper than the expected water cloud base level, between 5 and 27 bar depending on the assumed abundance of water ice lofted by thunderstorms and on the assumed ventilation coefficient governing heat transport between the atmosphere and the mushball. Because the ammonia is located mostly in the core of the mushballs, it tends to be delivered deeper than water, increasing the efficiency of the process. Further sinking of the condensates is expected due to cold temperature and ammonia‐ and water‐rich downdrafts formed by the evaporation of mushballs. This process can thus potentially account for the measurements of ammonia depletion in Jupiter’s deep atmosphere.Plain Language SummaryThe Juno mission has revealed that Jupiter’s atmosphere is much more complex and intriguing than previously anticipated. Most of Jupiter’s atmosphere was shown to be depleted in ammonia. While ammonia was expected to be well mixed, large scale variability of ammonia was detected at least 100 km below the cloud level where condensation occurs. We propose a mechanism to explain this depletion and variability. We show that in Jupiter, at very low temperatures (of order −90° C), water ice and ammonia vapor combine to form a liquid and we hypothesize that this subsequently triggers unexpected meteorology. During Jupiter’s violent storms, hailstones form from this liquid, similar to the process in terrestrial storms where hail forms in the presence of supercooled liquid water. Growth of the hailstones creates a slush‐like substance surrounded by a layer of ice, and these “mushballs” fall, evaporate, and continue sinking further in the planet’s deep atmosphere, creating both ammonia depletion and variability, potentially explaining the Juno observations.Key PointsWe show that ammonia can melt water‐ice crystals in Jupiter’s storms and lead to the formation of water‐ammonia hailstones (mushballs)These mushballs and subsequent downdrafts transport ammonia to very deep levelsThis can potentially explain Juno measurements that Jupiter’s ammonia abundance is variable until at least 150 km below the visible cloudsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156131/2/jgre21375.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156131/1/jgre21375_am.pd

Juno Jiram Report jm0350

This document describes the activities that JIRAM performed during the activity period JM0350 (PJ035), with particular attention to the comparison between the expected and returned data, keeping track of the instrument configuration with the commanding file (SASF)

Juno Jiram Report jm0410

This document describes the activities that JIRAM performed during the activity period JM0410 (PJ041), with particular attention to the comparison between the expected and returned data, keeping track of the instrument configuration with the commanding file (SASF)

Juno Jiram Report jm0360

This document describes the activities that JIRAM performed during the activity period JM0360 (PJ036), with particular attention to the comparison between the expected and returned data, keeping track of the instrument configuration with the commanding file (SASF)

Juno Jiram Report jm0400

This document describes the activities that JIRAM performed during the activity period JM0400 (PJ040), with particular attention to the comparison between the expected and returned data, keeping track of the instrument configuration with the commanding file (SASF)

Juno Jiram Report jm0420

This document describes the activities that JIRAM performed during the activity period JM0420 (PJ042), with particular attention to the comparison between the expected and returned data, keeping track of the instrument configuration with the commanding file (SASF)

Juno Jiram Report jm0390

This document describes the activities that JIRAM performed during the activity period JM0390 (PJ039), with particular attention to the comparison between the expected and returned data, keeping track of the instrument configuration with the commanding file (SASF)

Juno Jiram Report jm0370

This document describes the activities that JIRAM performed during the activity period JM0370 (PJ037), with particular attention to the comparison between the expected and returned data, keeping track of the instrument configuration with the commanding file (SASF)

Juno Jiram report jm0380

This document describes the activities that JIRAM performed during the activity period JM0380 (PJ038), with particular attention to the comparison between the expected and returned data, keeping track of the instrument configuration with the commanding file (SASF)