Observing the timescales of aerosol–cloud interactions in snapshot satellite images

The response of cloud processes to an aerosol perturbation is one of the largest uncertainties in the anthropogenic forcing of the climate. It occurs at a variety of timescales, from the near-instantaneous Twomey effect to the longer timescales required for cloud adjustments. Understanding the temporal evolution of cloud properties following an aerosol perturbation is necessary to interpret the results of so-called “natural experiments” from a known aerosol source such as a ship or industrial site. This work uses reanalysis wind fields and ship emission information matched to observations of ship tracks to measure the timescales of cloud responses to aerosol in instantaneous (or“snapshot”) images taken by polar-orbiting satellites. As in previous studies, the local meteorological environment is shown to have a strong impact on the occurrence and properties of ship tracks, but there is a strong time dependence in their properties. The largest droplet number concentration (Nd) responses are found within 3 h of emission, while cloud adjustments continue to evolve over periods of 10 h or more. Cloud fraction is increased within the early life of ship tracks, with the formation of ship tracks in otherwise clear skies indicating that around 5 %–10 % of clear-sky cases in this region may be aerosol-limited. The liquid water path (LWP) enhancement and the Nd–LWP sensitivity are also time dependent and strong functions of the background cloud and meteorological state. The near-instant response of the LWP within ship tracks may be evidence of a bias in estimates of the LWP response to aerosol derived from natural experiments. These results highlight the importance of temporal development and the background cloud field for quantifying the aerosol impact on clouds, even in situations where the aerosol perturbation is clear.

Small-scale geological mapping on Earth: Setting up guidelines, standards and portrayal rules. Experience from pan-European projects

<p>Geological mapping and cartography on Earth encompasses principally the description of the landforms, i.e. geomorphology, the lithology and the age (stratigraphy) of the rocks found at or beneath the Earth’s surface. By interpretation of this information genetic information (process, event and environment) can be derived from the rock units encountered and often is included in geological maps, in particular in larger scale maps.</p><p>Mapping agencies and geological survey organisations everywhere have for centuries been developing their own regional or national mapping methods and representation colour sets and symbols to represent the geological information on paper and now in spatial databases and GIS.</p><p>BGR and its predecessors has been undertaking geological mapping at both large and small scales since the 19<sup>th</sup> century and through this has gained considerable mapping experience. This contribution describes the establishment of mapping rules and guidelines for three small-scale European cross-boundary mapping projects implemented through international cooperation: the IGME 5000 (pre-Quaternary) and the IQUAME (Quaternary) projects, and the EMODnet Geology seafloor work-package. The experience gained within the projects in the creation and use of standardised specifications for data models and cartographic aspects such as symbols and colours will be introduced and challenges, advantages and disadvantages  will be discussed.</p><p>All three projects include off-shore geological information; in particular these aspects of the marine mapping and cartography may be partly comparable to planetary mapping, since “even with all the technology that we have today -- satellites, buoys, underwater vehicles and ship tracks -- we have better maps of the surface of Mars and the Moon than we do the bottom of the ocean.” [Gene Feldmann, NASA, 10.08.2009].</p><p>Thus the experience and results in Earth mapping described may contribute and serve as “good practise” for the benefit of the fascinating new field of planetary mapping.</p><p> </p>

Salinity variability in satellite subpixels: impact on satellite in-situ comparisons.

<p>Sea Surface Salinity (SSS) are retrieved from SMOS and SMAP L-band radiometers at a spatial resolution of about 50km.</p><p> </p><p>Traditionally, satellite SSS products validation is based on comparisons with in-situ near surface salinity measurements.</p><p> </p><p>In-situ measurements are performed on moorings, argo floats and along ship tracks[JB1] , which provide punctual or one-dimensional (along ship tracks) estimations of the SSS.</p><p> </p><p>The sampling difference between one-dimensional or punctual in-situ measurements and two-dimensional satellite products results in a sampling error that must be separated from measurement errors for the validation of satellite products.</p><p> </p><p>We use a small-scale resolution field (1/12° Mercator Global Ocean Physics Analysis and Forecast) to estimate the expected sampling error of each kind of in-situ measurements, by comparing punctual, [JB2] one-dimensional and two-dimensional SSS variability.</p><p> </p><p>The better understanding of sampling errors allows a more accurate validation of satellite SSS and of the errors estimated by satellite retrieval algorithms. The improvement is quantified by considering the standard deviation of satellite minus in-situ salinities differences normalized by the sampling and retrieval errors. This quantity should be equal to one if all the error contributions are correctly considered. This methodology will be applied to SMOS SSS and to merged SMOS and SMAP SSS products.</p>

Vessel Trajectory Analysis in Designated Harbor Route Considering the Influence of External Forces

A vessel must navigate along designated routes within a harbor area to ensure navigation safety. The impact of strong currents is one of the most dangerous factors in coastal navigation. However, it is challenging to determine the deviation of a ship in advance from the ship’s position data in the case of a marine accident. In this study, to support the decision-making of ship navigators and vessel traffic service (VTS) operators in track monitoring tasks, tracks were classified according to the tidal stream, and the track distribution was analyzed according to the tidal current situations. Marine accident analysis was performed to investigate the tidal influence on ship tracks. Track data were collected for 12 months from a VTS center in Korea, and tidal information was collected through a meteorological observation buoy. Representative tracks were extracted from the track data using the support vector regression (SVR) seaway model. K-fold cross-validation and a grid search were performed to determine the optimal parameters. The ship tracks appeared in specific patterns according to the forces and directions of tidal currents, and specific deviation patterns were observed. This study is expected to contribute to the reduction of marine accidents by predicting ship trajectories according to the tidal situations in advance.

How Spice is Stirred in the Bay of Bengal

The scale-dependent variance of tracer properties in the ocean bears the imprint of the oceanic eddy field. Anomalies in spice (which combines anomalies in temperature T and salinity S on isopycnal surfaces) act as passive tracers beneath the surface mixed layer (ML). We present an analysis of spice distributions along isopycnals in the upper 200 m of the ocean, calculated with over 9000 vertical profiles of T and S measured along ~4800 km of ship tracks in the Bay of Bengal. The data are from three separate research cruises—in the winter monsoon season of 2013 and in the late and early summer monsoon seasons of 2015 and 2018. We present a spectral analysis of horizontal tracer variance statistics on scales ranging from the submesoscale (~1 km) to the mesoscale (~100 km). Isopycnal layers that are closer to the ML-base exhibit redder spectra of tracer variance at scales km than is predicted by theories of quasigeostrophic turbulence or frontogenesis. Two plausible explanations are postulated. The first is that stirring by submesoscale motions and shear dispersion by near-inertial waves enhance effective horizontal mixing and deplete tracer variance at horizontal scales km in this region. The second is that the spice anomalies are coherent with dynamical properties such as potential vorticity, and not interpretable as passively stirred.

Exploring the aerosol-cloud-radiation relationships in deep marine stratocumulus layers

<p>Marine stratocumuli cover around a fifth of the worlds oceans and are a key contributor to Earth’s radiative balance at the surface. Their sensitivity to changes in anthropogenic aerosol concentrations remain a key uncertainty in the climate system. Our current understanding of their sensitivity and the plausible range of the aerosol-cloud radiative forcing is largely based on the process understanding obtained from field campaigns, high-resolution modelling, and satellite records of aerosol-induced phenomena such as volcano or ship tracks.</p><p>Yet, a large fraction of these records is only applicable to relatively shallow planetary boundary layers (PBLs). Ship tracks are only found in boundary layers up to a depth of 800m. Field campaigns and high-resolution modelling studies of aerosol-cloud-radiation interactions in marine stratocumuli have been restricted to a similar range of PBL depths in the past. Meanwhile over 70% of marine boundary layers reside in deeper PBLs.</p><p>The liquid water path (LWP) adjustment due to aerosol-cloud interactions in marine stratocumuli remains a considerable source of uncertainty for climate sensitivity estimates. An unequivocal attribution of LWP adjustments to changes in aerosol concentration from climatology remains difficult due to the considerable covariance between meteorological conditions alongside changes in aerosol concentrations.</p><p>Here, we combine a range of space-born remote sensing retrievals to investigate the relationship of cloud-radiative properties for different boundary layer depths and aerosol concentrations. As done in previous studies we utilise the susceptibility framework, i.e. the relative change in LWP scaled by the relative change in cloud droplet number concentration, to quantify the change in LWP adjustment with PBL depth. We show that the susceptibility of LWP adjustments triples in magnitude from values of -0.1 in PBLs shallower than 0.5 km to -0.33 in PBLs deeper than 1 km.</p><p>We further argue that LWP susceptibility estimates inferred from deep PBL climatologies are poorly constrained due to a lack of process-oriented observations. Meanwhile, susceptibilities inferred from climatology in shallow PBL regimes are consistent with estimates obtained from process modelling studies, but are overestimated as compared to pollution track estimates.</p>

Investigating contrails within cirrus clouds

<p>Effects of aviation on the Earth’s radiation budget and climate related to CO<sub>2</sub> emissions and from the formation of linear contrails and contrail cirrus have been the focus of detailed studies. Aviation effects on existing cirrus clouds are much less investigated. Contrail formation in existing cirrus clouds has the potential to increase the cloud optical thickness (COT) of optically thin cirrus, which might result in a net cooling effect.</p><p>Spaceborne remote sensing generally provides the means for studying the impact of aviation on climate. However, only active instruments such as lidar or radar can be used to study the effect of contrails that form within existing cirrus clouds. For such an investigation, the location of an aircraft at a given time needs to be matched with information on cloud coverage, cloud type, cloud layer height, and COT as can be retrieved from spaceborne CALIPSO lidar data.</p><p>We have developed an algorithm to find intersections of aircraft flight tracks with satellite tracks. Besides the spatial coordinates, the time difference between the passing of the aircraft and the satellite at the intersection is monitored and relevant aircraft data and satellite recordings are retrieved at the intersection. The algorithm is highly adjustable so that it can be adapted for other applications such as investigation of ship tracks or cloud tracking. The new algorithm has been used to identify aircraft flying through cirrus clouds in remote regions of the Earth to study the effects of individual aircraft on existing cirrus.</p>

Algorithm Spots Climate-Altering Ship Tracks in Satellite Data

Tens of thousands of ship tracks—cloud structures created when ships’ exhaust plumes interact with the atmosphere—are pinpointed automatically, furthering study of these climate-altering features.