ALBERT

Description: This paper evaluates the suitability of the ECOSSE model to estimate soil greenhouse gas fluxes from short rotation coppice willow (SRC-Willow), short rotation forestry (SRF-Scots Pine) and Miscanthus after land-use change from conventional systems (grassland and arable). We simulate heterotrophic respiration (R h ), nitrous oxide (N 2 O) and methane (CH 4 ) fluxes at four paired sites in the UK, and compare them to estimates of R h derived from the ecosystem respiration estimated from eddy covariance (EC) and R h estimated from chamber (IRGA) measurements, as well as direct measurements of N 2 O and CH 4 fluxes. Significant association between modelled and EC-derived R h was found under Miscanthus , with correlation coefficient ( r ) ranging between 0.54 and 0.70. Association between IRGA-derived R h and modelled outputs was statistically significant at the Aberystwyth site ( r = 0.64) but not significant at the Lincolnshire site ( r = 0.29). At all SRC-Willow sites, significant association was found between modelled and measurement-derived R h (0.44 ≤ r ≤ 0.77); significant error was found only for the EC-derived R h at the Lincolnshire site. Significant association and no significant error were also found for SRF-Scots Pine and perennial grass. For the arable fields, the modelled CO 2 correlated well just with the IRGA-derived R h at one site ( r = 0.75). No bias in the model was found at any site, regardless of the measurement type used for the model evaluation. Across all land-uses, fluxes of CH 4 and N 2 O were shown to represent a small proportion of the total greenhouse gas balance; these fluxes have been modelled adequately on a monthly time-step. This study provides confidence in using ECOSSE for predicting the impacts of future land-use on greenhouse gas balance, at site level as well as at national level. This article is protected by copyright. All rights reserved.

Description: Given the strong coupling between the carbon (C) and nitrogen (N) cycles, there is substantial interest in understanding how N availability affects C cycling in terrestrial ecosystems, especially in ecosystems limited by N. However, most studies in temperate and boreal forests have focused on the effects of N addition on tree growth. By comparison, less is known about the effects of N availability on the cycling of C in understory vegetation despite some evidence that dwarf shrubs, mosses, and lichens play an important role in the forest C balance. In this study, we used an in situ 13 CO 2 pulse-labelling technique to examine the short-term dynamics of C partitioning in understory vegetation in three boreal Pinus sylvestris forest stands exposed to different rates of N addition: a low and high N addition that receive annual additions of NH 4 NO 3 of 20 and 100 kg N ha −1 , respectively, and an unfertilized control. Labelling was conducted at two distinct periods (early vs . late growing season), which provided a seasonal picture of how N addition affects C dynamics in understory vegetation. In contrast to what has been found in trees, there was no obvious trend in belowground C partitioning in ericaceous plants in response to N additions or seasonality. Increasing N addition led to a greater percentage of 13 C being incorporated into ericaceous leaves with a high turnover, whereas high rates of N addition strongly reduced the incorporation of 13 C into less degradable moss tissues. Addition of N also resulted in a greater percentage of the 13 C label being respired back to the atmosphere and an overall reduction in total understory carbon-use-efficiency. Taken together, our results suggest a faster cycling of C in understory vegetation with increasing N additions; yet the magnitude of this general response was strongly dependent on the amount of N added and varied seasonally. These results provide some of the first in situ C and N partitioning estimates for plants growing under the complex web of resource limitations in the boreal understory. This article is protected by copyright. All rights reserved.

Description: New analysis of the Doppler shift of O2 airglow spectra recorded by the TIMED Doppler Interferometer (TIDI) and the High Resolution Doppler Imager (HRDI) have provided conclusive evidence that the shuttle main engine exhaust plume generated in the lower thermosphere by the launch of STS-107 and imaged by the Global Ultraviolet Imager (GUVI) instrument on TIMED was transported to the Antarctic in ∼80 h, supporting a key inference from the initial study by Stevens et al. (2005). These new results were aided by improved knowledge of the effects of instrumental and satellite artifacts imposed on the Doppler spectra. STS-107 launched on 16 January 2003, and the neutral wind near its launch trajectory and nearby volume was sampled within minutes by TIDI. These initial observations suggested that the northernmost end of the shuttle's exhaust plume would move northeast and that the southern end would move southeast, motions that were identified in imagery acquired during the next orbit of TIMED. The direction and magnitude of plume motion inferred from GUVI images obtained 12, 26, and 50 h after launch were again confirmed by TIDI and HRDI. The appearance of the plume over the Antarctic ∼80 h after launch, inferred from earlier work by the appearance of iron ablated from the shuttle's main engines, was consistent with neutral winds measured by the satellite Doppler instruments over the Antarctic. The transport of the plume from the coast of Florida to the Antarctic was aided by the favorable phase and strong amplitude of a 2 day planetary wave of wave number three in the southern hemisphere on 18 January 2003. The existence of the 2 day wave was deduced from zonally averaged and combined TIDI and HRDI neutral wind observations. We conclude that the existence of strong and sustained winds in the MLT, significantly greater than expected from empirical and theoretical models, is indisputable and provides compelling evidence supporting the global-scale nature of thermospheric winds with magnitude greater than 100 m/s observed by Larsen (2002) from 40 years of sounding rocket chemical release experiments.

Description: Presented is an analysis of the occurrence of post-sunset Equatorial Plasma Bubbles (EPBs) detected using a Global Positioning System (GPS) receiver at Vanimo. The 3-year dataset shows that the EPB occurrence maximizes (minimizes) during the equinoxes (solstices), in good agreement with previous findings. The Vanimo ionosonde station is used with the GPS receiver in an analysis of the day-to-day EPB occurrence variability during the 2000 equinox period. A superposed epoch analysis (SEA) reveals that the altitude, and the change in altitude, of the F layer height is ~1 standard deviation (1 σ ) larger on the days for which EPBs were detected, compared to non-EPB days. These results are then compared to results from the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM), which show strong similarities with the observations. The TIEGCM is used to calculate the flux-tube integrated Rayleigh-Taylor (R-T) instability linear growth rate. A SEA reveals that the modeled R-T growth rate is 1 σ higher on average for EPB days compared to non-EPB days, and that the upward plasma drift is the most dominant contributor. It is further demonstrated that the TIEGCM's success in describing the observed daily EPB variability during the scintillation season resides in the variations caused by geomagnetic activity (as parameterized by Kp) rather than solar EUV flux (as parameterized by F10.7). Geomagnetic activity varies the modeled high-latitude plasma convection andthe associated Joule heating that affects the low-latitude F-region dynamo, and consequently the equatorial upward plasma drift.

Description: Abstract Given the strong coupling between the carbon (C) and nitrogen (N) cycles, there is substantial interest in understanding how N availability affects C cycling in terrestrial ecosystems, especially in ecosystems limited by N. However, most studies in temperate and boreal forests have focused on the effects of N addition on tree growth. By comparison, less is known about the effects of N availability on the cycling of C in understory vegetation despite some evidence that dwarf shrubs, mosses, and lichens play an important role in the forest C balance. In this study, we used an in situ 13CO2 pulse‐labelling technique to examine the short‐term dynamics of C partitioning in understory vegetation in three boreal Pinus sylvestris forest stands exposed to different rates of N addition: a low and high N addition that receive annual additions of NH4NO3 of 20 and 100 kg N ha−1, respectively, and an unfertilized control. Labelling was conducted at two distinct periods (early vs. late growing season), which provided a seasonal picture of how N addition affects C dynamics in understory vegetation. In contrast to what has been found in trees, there was no obvious trend in belowground C partitioning in ericaceous plants in response to N additions or seasonality. Increasing N addition led to a greater percentage of 13C being incorporated into ericaceous leaves with a high turnover, whereas high rates of N addition strongly reduced the incorporation of 13C into less degradable moss tissues. Addition of N also resulted in a greater percentage of the 13C label being respired back to the atmosphere and an overall reduction in total understory carbon‐use‐efficiency. Taken together, our results suggest a faster cycling of C in understory vegetation with increasing N additions; yet the magnitude of this general response was strongly dependent on the amount of N added and varied seasonally. These results provide some of the first in situ C and N partitioning estimates for plants growing under the complex web of resource limitations in the boreal understory. This article is protected by copyright. All rights reserved.

Description: Given the strong coupling between the carbon (C) and nitrogen (N) cycles, there is substantial interest in understanding how N availability affects C cycling in terrestrial ecosystems, especially in ecosystems limited by N. However, most studies in temperate and boreal forests have focused on the effects of N addition on tree growth. By comparison, less is known about the effects of N availability on the cycling of C in understory vegetation despite some evidence that dwarf shrubs, mosses, and lichens play an important role in the forest C balance. In this study, we used an in situ 13 CO 2 pulse-labeling technique to examine the short-term dynamics of C partitioning in understory vegetation in three boreal Pinus sylvestris forest stands exposed to different rates of N addition: a low and high N addition that receive annual additions of NH 4 NO 3 of 20 and 100 kg N/ha, respectively, and this is a typo. It should be an unfertilized control. Labeling was conducted at two distinct periods (early vs. late growing season), which provided a seasonal picture of how N addition affects C dynamics in understory vegetation. In contrast to what has been found in trees, there was no obvious trend in belowground C partitioning in ericaceous plants in response to N additions or seasonality. Increasing N addition led to a greater percentage of 13 C being incorporated into ericaceous leaves with a high turnover, whereas high rates of N addition strongly reduced the incorporation of 13 C into less degradable moss tissues. Addition of N also resulted in a greater percentage of the 13 C label being respired back to the atmosphere and an overall reduction in total understory carbon use efficiency. Taken together, our results suggest a faster cycling of C in understory vegetation with increasing N additions; yet the magnitude of this general response was strongly dependent on the amount of N added and varied seasonally. These results provide some of the first in situ C and N partitioning estimates for plants growing under the complex web of resource limitations in the boreal understory.