Instrument intercomparison study on cloud droplet size distribution measurements: Holography vs. laser optical particle counter

During the EUROTRAC Ground Based Cloud Experiment (GCE) 1990, a newly developed HODAR (Holographic Droplet and Acrosol Recording) was operated for the first time to measure cloud droplet size distributions by recording Fraunhofer in-line holograms of small cloud sample volumes in situ and analyzing the holographic images in the laboratory.This technical note compares the resulting size distributions with those obtained from two FSSP-100 laser optical particle counters. For all holograms analyzed during the GCE90 field experiment, the size distributions obtained from the two different methods agree well. Additionally, the liquid water contents (LWC) were measured directly by a Gerber particulate volume monitor PVM-100. The LWC calculated from the measured droplet size distributions deviate from the PVM-100 data.     

A model for the deep structure of the East African rift system from simultaneous inversion of teleseismic data

Simultaneous inversion of teleseismic data results in a model for the western branch of the East African Rift system between 1°S and 10°N characterized by a 35 km crust and thin high-velocity lid, overlying a channel possessing both low S and low P velocities (4.47 and 7.69 km/sec, respectively). A strong reflector at 140 km depth marks the boundary to high-velocity material (4.67 and 8.44 km/sec, respectively).The eastern branch has a crustal thickness of 40 km and is characterized by low S velocities, 4.43 km/sec in the lid to a depth of 78 km, 4.09–4.21 km/sec in a channel which extends to 161 km depth. The S velocities remain relatively low at greater depths, but cannot be precisely determined because of the limited resolution.We have interpreted these and other geophysical data as due to a diapiric intrusion of material with a high pyroxene content and possibly with some low-density eclogite, coming from the mesosphere. A mushroom of this rock has stalled below the western branch at about 55 km below the surface and is cooling. The diapirism in the eastern branch has broken through to the surface. The mantle of the African shield to the west of the Rift shows seismic velocities which indicate that it is depleted in basaltic components.     

Well modeling and estimation of hydraulic parameters

A general model for time‐dependent saturated–unsaturated waterflow caused by a single well with a given radius is presented. The storage capacity of the well tube is taken into account. The inflow into the well (with drainage) is modeled using the Signorini boundary condition. The nonconforming mixed finite element method on a multilevel adaptive grid is used for the solution of the radial symmetric, time dependent problem. Finally, van Genuchten parameters of an aquifer are determined from field measurements by inverse computations.     

The Impact of the Afternoon Planetary Boundary-Layer Height on the Diurnal Cycle of CO and $$\hbox {CO}_{2}$$ Mixing Ratios at a Low-Altitude Mountaintop

Mountaintop trace-gas mixing ratios are often assumed to represent free atmospheric values, but are affected by valley planetary boundary-layer (PBL) air at certain times. We hypothesize that the afternoon valley–PBL height relative to the ridgetop is important in the diurnal cycle of mountaintop trace-gas mixing ratios. To investigate this, we use, (1) 4-years (1 January 2009–31 December 2012) of CO and \(\hbox {CO}_{2}\) mixing-ratio measurements and supporting meteorological observations from Pinnacles (\(38.61^{\circ }\hbox {N}\), \(78.35^{\circ }\hbox {W}\), 1017 m a.s.l.), which is a monitoring site in the Appalachian Mountains, (2) regional \(\hbox {O}_{3}\) mixing-ratio measurements, and (3) PBL heights determined from a nearby sounding station. Results reveal that the amplitudes of the diurnal cycles of CO and \(\hbox {CO}_{2}\) mixing ratios vary as a function of the daytime maximum valley–PBL height relative to the ridgetop. The mean diurnal cycle for the subset of days when the afternoon valley–PBL height is at least 400 m below the ridgetop shows a daytime CO mixing-ratio increase, implying the transport of PBL air from the valley to the mountaintop. During the daytime, on days when the PBL heights exceed the mountaintop, PBL dilution and entrainment cause CO mixing ratios to decrease. This decrease in CO mixing ratio, especially on days when PBL heights are at least 400 m above the ridgetop, suggests that measurements from these days can be used as with afternoon measurements from flat terrain in applications requiring regionally-representative measurements.     

A Surface-Layer Study of the Transport and Dissipation of Turbulent Kinetic Energy and the Variances of Temperature,Humidity and CO$$_$$

We discuss scalar similarities and dissimilarities based on analysis of the dissipation terms in the variance budget equations, considering the turbulent kinetic energy and the variances of temperature, specific humidity and specific CO\(_2\) content. For this purpose, 124 high-frequency sampled segments are selected from the Boundary Layer Late Afternoon and Sunset Turbulence experiment. The consequences of dissipation similarity in the variance transport are also discussed and quantified. The results show that, for the convective atmospheric surface layer, the non-dimensional dissipation terms can be expressed in the framework of Monin–Obukhov similarity theory and are independent of whether the variable is temperature or moisture. The scalar similarity in the dissipation term implies that the characteristic scales of the atmospheric surface layer can be estimated from the respective rate of variance dissipation, the characteristic scale of temperature, and the dissipation rate of temperature variance.     

Using detrital zircon U‐Pb ages to calculate Late Cretaceous sedimentation rates in the Magallanes‐Austral basin,Patagonia

Determining both short‐ and long‐term sedimentation rates is becoming increasingly important in geomorphic (exhumation and sediment flux), structural (subsidence/flexure) and natural resource (predictive modelling) studies. Determining sedimentation rates for ancient sedimentary sequences is often hampered by poor understanding of stratigraphic architecture, long‐term variability in large‐scale sediment dispersal patterns and inconsistent availability of absolute age data. Uranium–Lead (U‐Pb) detrital zircon (DZ) geochronology is not only a popular method to determine the provenance of siliciclastic sedimentary rocks but also helps delimit the age of sedimentary sequences, especially in basins associated with protracted volcanism. This study assesses the reliability of U‐Pb DZ ages as proxies for depositional ages of Upper Cretaceous strata in the Magallanes‐Austral retroarc foreland basin of Patagonia. Progressive younging of maximum depositional ages (MDAs) calculated from young zircon populations in the Upper Cretaceous Dorotea Formation suggests that the MDAs are potential proxies for absolute age, and constrain the age of the Dorotea Formation to be ca. 82–69 Ma. Even if the MDAs do not truly represent ages of contemporaneous volcanic eruptions in the arc, they may still indicate progressive‐but‐lagged delivery of increasingly younger volcanogenic zircon to the basin. In this case, MDAs may still be a means to determine long‐term (≥1–2 Myr) average sedimentation rates. Burial history models built using the MDAs reveal high aggradation rates during an initial, deep‐marine phase of the basin. As the basin shoaled to shelfal depths, aggradation rates decreased significantly and were outpaced by progradation of the deposystem. This transition is likely linked to eastward propagation of the Magallanes fold‐thrust belt during Campanian‐Maastrichtian time, and demonstrates the influence of predecessor basin history on foreland basin dynamics.     

Characterisation and diachronous initiation of coarse clastic deposition in the Magallanes–Austral foreland basin,Patagonian Andes

Magallanes–Austral Basin (MAB) fill is preserved along a >1000 km north–south trending outcrop belt in the southern Patagonia region of Argentina and Chile. Although the stratigraphic evolution of the MAB has been well documented in the Chilean sector (referred to as the Magallanes Basin), its northern terminus in southern Argentina (Austral Basin) is poorly constrained. We present new stratigraphic and geochronologic analyses of the early basin fill (Aptian–Turonian) from the Argentine sector (49–51°S) of the MAB to document spatial variability in stratigraphy and timing of deposition during the initial stages of basin evolution. The initiation of the retroarc foreland basin fill is marked by the transition from mudstone to coarse‐clastic deposition, which is characterised by the consistent presence of sandstone beds > ca. 20 cm thick interpreted to represent sediment gravity flows deposited in a submarine fan system. Depositional environments within the early fill of the basin range from lower to upper deep‐water fan settings as well as previously undocumented slope deposits. These facies are present as far north as El Chalten, Argentina (ca. 49°S), indicating that facies‐equivalent rocks can be traced along‐strike for at least 5 degrees of latitude, based on correlation with strata as far south as the Cordillera Darwin (ca. 54°S). Eight new U‐Pb zircon ages from ash beds reveal an overall southward younging trend in the initiation of coarse clastic deposition. Inferred depositional ages range from ca. 115 ± 1.9 Ma in the northernmost study area to not older than 92 ± 1 Ma and 89 ± 1.5 Ma in the central and southern sectors respectively. The apparent diachronous delivery of coarse detritus into the basin may reflect (1) gradual southward progradation of a deep‐water fan system from a northerly point source and/or (2) orogen‐parallel variations in the timing and magnitude of thrust‐belt deformation and erosion that provided more local sources for sediment delivery.