Effects of soil moisture, net radiation, and atmospheric vapor pressure deficit on surface evaporation fraction at a semi-arid grass site.

Surface energy partitioning is one of the most important aspects of the land-atmosphere coupling. The objective of this study is to examine how soil moisture (SM) and atmospheric conditions (net radiation, Rn and vapor pressure deficit, VPD) affect surface evaporation fraction (EF, determined by LE/(LE + H), where LE and H are latent and sensible heat flux, respectively) with measurements at a semi-arid grass site in China during the mid-growing season, 2020. The three factors (SM, Rn, and VPD) were divided into different levels, and then their effects on EF were investigated qualitatively using a combinatorial stratification method and quantificationally using a path analysis. Generally, the results indicated that the effect of one factor of SM, Rn and VPD on EF was influenced by the other two factors. EF tended to increase with increasing SM. Increased VPD (Rn) enhanced (weakened) the SM-EF relationship. When soil was dry, EF tended to decrease with increasing VPD; when soil was wet, EF initially levelled off and then decreased with increasing VPD. Increased Rn enhanced (weakened) the positive (negative) effect of VPD on EF when soil was wet (dry). In terms of Rn effect, EF tended to decrease as Rn increases. Further, path analysis suggested that SM, Rn, and VPD not only directly affected EF, but also indirectly affected EF, mainly through canopy conductance (Gs) and temperature difference between land surface and air (∆T). The direct effect of SM accounted for >50 % of its total effect on EF, while the total effects of Rn and VPD on EF were dominated by their indirect effects. These observational evidences may have implications for improving representation of land-atmosphere coupling in atmospheric general circulation models over the semi-arid regions covered by grass.

Monitoring atmospheric nitrous oxide background concentrations at Zhongshan Station, east Antarctica.

At present, continuous observation data for atmospheric nitrous oxide (N2O) concentrations are still lacking, especially in east Antarctica. In this paper, nitrous oxide background concentrations were measured at Zhongshan Station (69°22'25″S, 76°22'14″E), east Antarctica during the period of 2008-2012, and their interannual and seasonal characteristics were analyzed and discussed. The mean N2O concentration was 321.9nL/L with the range of 320.5-324.8nL/L during the five years, and it has been increasing at a rate of 0.29% year(-1). Atmospheric N2O concentrations showed a strong seasonal fluctuation during these five years. The concentrations appeared to follow a downtrend from spring to autumn, and then increased in winter. Generally the highest concentrations occurred in spring. This trend was very similar to that observed at other global observation sites. The overall N2O concentration at the selected global sites showed an increasing annual trend, and the mean N2O concentration in the Northern Hemisphere was slightly higher than that in the Southern Hemisphere. Our result could be representative of atmospheric N2O background levels at the global scale. This study provided valuable data for atmospheric N2O concentrations in east Antarctica, which is important to study on the relationships between N2O emissions and climate change.

High variability of atmospheric mercury in the summertime boundary layer through the central Arctic Ocean.

The biogeochemical cycles of mercury in the Arctic springtime have been intensively investigated due to mercury being rapidly removed from the atmosphere. However, the behavior of mercury in the Arctic summertime is still poorly understood. Here we report the characteristics of total gaseous mercury (TGM) concentrations through the central Arctic Ocean from July to September, 2012. The TGM concentrations varied considerably (from 0.15 ng/m(3) to 4.58 ng/m(3)), and displayed a normal distribution with an average of 1.23 ± 0.61 ng/m(3). The highest frequency range was 1.0-1.5 ng/m(3), lower than previously reported background values in the Northern Hemisphere. Inhomogeneous distributions were observed over the Arctic Ocean due to the effect of sea ice melt and/or runoff. A lower level of TGM was found in July than in September, potentially because ocean emission was outweighed by chemical loss.

Growth rate of Usnea aurantiacoatra (Jacq.) Bory on Fildes Peninsula, Antarctica and its climatic background.

The ages of a fruticose lichen of Usnea aurantiacoatra (Jacq.) Bory, from Fildes Peninsula, King George Island, Southwest Antarctic, were determined by radiocarbon (14C), and it is 1993-1996 at bottom and 2006-2007 at top of the lichen branch. The growth rates of U. aurantiacoatra calculated are 4.3 to 5.5 mm year(-1) based on its length and ages. The comparisons show that the growth rates of U. aurantiacoatra are higher than those of U. antarctica (0.4 to 1.1 mm year(-1)). The growth rates of fruticose lichens are always higher, usually >2 mm year(-1), than those of crustose ones, usually <1 mm year(-1), in polar areas. A warming trend on Fildes Peninsula is recorded in the period from 1969 to 2010 obviously: the mean annual temperature rose from -2.75 to -1.9°C and the average temperature of summer months from 0.95 to 1.4°C, as well as the average temperature of winter months from -6.75 to -5.5°C. The alteration of lichen growth rates in polar areas may respond to the climatic and environmental changes, and the lichens may act as bio-monitor of natural condition.

[The retrieval of ozone column densities by passive differential optical absorption spectroscopy during summer at Zhongshan Station, Antarctic].

Daily ozone column densities were monitored by Passive DOAS (differential optical absorption spectroscopy) from December 10th, 2008 to Feb 19th, 2009 at Zhongshan Station, Antarctic (69 degrees 22'24" S, 76 degrees 22'14" E). Considering the absorption of O3, OClO, NO2, O4, BrO and the Ring effect, ozone slant column densities were retrieved using the zenith scattered sunlight as the light source. The results showed that there was no obvious "ozone hole" during the monitoring period, but ozone VCD (vertical column density) had greatly changed within short time scale, especially in middle December and early February. The analysis of passive DOAS and Brewer measurements of ozone VCD showed good agreement with the correlative coefficient of 0.863, while satellite board OMI measurements with the correlative coefficient of 0.840, which confirmed the validity of the monitoring of Passive DOAS.