Decoupling of a Douglas fir canopy: a look into the subcanopy with continuous vertical temperature profiles

Complex ecosystems such as forests make accurately measuring atmospheric energy and matter fluxes difficult. One of the issues that can arise is that parts of the canopy and overlying atmosphere can be turbulently decoupled from each other, meaning that the vertical exchange of energy and matter is reduced or hampered. This complicates flux measurements performed above the canopy. Wind above the canopy will induce vertical exchange. However, stable thermal stratification, when lower parts of the canopy are colder, will hamper vertical exchange. To study the effect of thermal stratification on decoupling, we analyze high-resolution (0.3 m) vertical temperature profiles measured in a Douglas fir stand in the Netherlands using distributed temperature sensing (DTS). The forest has an open understory (0–20 m) and a dense overstory (20–34 m). The understory was often colder than the atmosphere above (80 % of the time during the night, >99 % during the day). Based on the aerodynamic Richardson number the canopy was regularly decoupled from the atmosphere (50 % of the time at night). In particular, decoupling could occur when both u*<0.4 m s−1 and the canopy was able to cool down through radiative cooling. With these conditions the understory could become strongly stably stratified at night. At higher values of the friction velocity the canopy was always well mixed. While the understory was nearly always stably stratified, convection just above the forest floor was common. However, this convection was limited in its vertical extent, not rising higher than 5 m at night and 15 m during the day. This points towards the understory layer acting as a kind of mechanical “blocking layer” between the forest floor and overstory. With the DTS temperature profiles we were able to study decoupling and stratification of the canopy in more detail and study processes which otherwise might be missed. These types of measurements can aid in describing the canopy–atmosphere interaction at forest sites and help detect and understand the general drivers of decoupling in forests.

Decoupling of a Douglas fir canopy: a look into the subcanopy with continuous vertical temperature profiles

Complex ecosystems such as forests make accurately measuring atmospheric energy and matter fluxes difficult. One of the issues that can arise is that parts of the canopy and overlying atmosphere can be turbulently decoupled from each other, meaning that the vertical exchange of energy and matter is reduced or hampered. This complicates flux measurements performed above the canopy. Wind above the canopy will induce vertical exchange. However, stable thermal stratification, when lower parts of the canopy are colder, will hamper vertical exchange. To study the effect of thermal stratification on decoupling, we analyze high resolution (0.3 m) vertical temperature profiles measured in a Douglas fir stand in the Netherlands using Distributed Temperature Sensing (DTS). The forest has an open understory (0–20 m) and a dense overstory (20–34 m). The understory was often colder than the atmosphere above (80 % of the time during the night, > 99 % during the day), and was regularly decoupled from the atmosphere (50 % of the time at night). The relationship between the temperature gradients and the friction velocity (u*) showed a clear threshold between coupling regimes. In particular, decoupling occurred when u*

Subducting filaments at fronts in the Alboran Sea: Physical, turbulent and biological evidences.

&lt;p&gt;Submesoscale instabilities along oceanic fronts can cause water mass intrusions from the surface mixed layer into the stratified pycnocline. These are important drivers of vertical exchange that have a potentially significant impact on the transfer of physical properties and biological tracers.&lt;/p&gt;&lt;p&gt;The CALYPSO (Coherent Lagrangian Pathways from the Surface Ocean to Interior) ONR research initiative focuses on observing and understanding coherent vertical pathways by which vertical exchange occurs. The Alboran Sea (located in the south-western Mediterranean, east of Gibraltar) is well known for its strong density fronts and eddies. During a research cruise, onboard &lt;em&gt;R/V Pourquoi Pas? &lt;/em&gt;in early April 2019&lt;em&gt;,&lt;/em&gt; we found that fronts in this area support the generation of subducting filaments. Several types of observations (using CTD, uCTD, microstructure profiles, drifters and floats) were collected along numerous cross-front transects over a period of two weeks.&lt;/p&gt;&lt;p&gt;The analysis of the temperature profiles highlighted the presence of several intruding filaments moving along isopycnal surfaces in the proximity of the frontal area. The intrusion signal was also clearly visible in biophysical properties with elevated Chlorophyll-a concentrations, well below the deep chlorophyll maximum, in conjunction with high dissolved oxygen values. From a microstructure point of view, the upper and lower limits of the subducting filaments exhibited high turbulent dissipation rates, with values of O(10&lt;sup&gt;-7&lt;/sup&gt;) W/m&lt;sup&gt;2&lt;/sup&gt;. These dissipation rates are higher than what is generally observed at such depths and point to enhanced mixing activity at the boundaries of the intrusions even along isopycnal surfaces.&lt;/p&gt;

Time lag between the tropopause height and the levels of 7Be concentrations in surface air

The concentration of 7Be at near surface air has been determined over 2009, which was a year of a deep solar minimum, at three different locations in Finland: Ivalo (68°64’N, 27°57’E), Rovaniemi (66°51’N, 25°68’E) and Kotka (60°48’N, 26°92’E). In geomagnetic latitudes over λ = 60° N, the elevation of tropopause during the warm summer months and the vertical exchange of air masses within the troposphere cause greater mixture of the air masses resulting in higher concentration levels for 7Be in surface air. However, different climatic phenomena, such as air masses from the East, make the correlation between the monthly activity concentrations of 7Be and the tropopause height fairly weak. For Ivalo and Rovaniemi it was found that changes in the daily surface concentrations of 7Be lag the changes in the elevation of the tropopause by four days. In Kotka, the correlation is weakest.

Water balance of Lake Gardno

The article describes the characteristics of water circulation in the coastal Lake Gardno. The water cycle is based on water balance data calculated for the period 2003–2007 concerning hydrological years, including the components of horizontal and vertical exchange. Due to the coastal location of the lake, particular attention was paid to the share of the seawater in the lake water cycle. It was found that the inflow of sea water accounts for 10% of the total inflow, while inflow from the land accounts for 86% of the total.

A Review on the Methods for Observing the Substance and Energy Exchange between Atmosphere Boundary Layer and Free Troposphere

Atmosphere boundary layer (ABL or BL) acts as a pivotal part in the climate by regulating the vertical exchange of moisture, aerosol, trace gases and energy between the earth surface and free troposphere (FT). However, compared with research on the exchange between earth surface and ABL, there are fewer researches on the exchange between ABL and FT, especially when it comes to the quantitative measurement of vertical exchange flux between them. In this paper, a number of various methodologies for investigating the exchange of the substance and energy between ABL and FT are reviewed as follows: (1) methods to obtain entrainment rate, which include method by investigating the height of inversion layer, method of flux-jump, estimating with dataset from the ASTEX Lagrangian Experiments and method of using satellite observations and Microwave Imager; (2) mass budget method, which can yield quantitative measurements of exchange flux between ABL and FT; (3) qualitative measurements: method based on Rayleigh distillation and mixing processes, methods of ground-based remote sensing and airborne tracer-tracer relationship/ratio method.