Latitude Band Research Articles

Constraining the low‐cloud optical depth feedback at middle and high latitudes using satellite observations

AbstractThe increase in cloud optical depth with warming at middle and high latitudes is a robust cloud feedback response found across all climate models. This study builds on results that suggest the optical depth response to temperature is timescale invariant for low‐level clouds. The timescale invariance allows one to use satellite observations to constrain the models' optical depth feedbacks. Three passive‐sensor satellite retrievals are compared against simulations from eight models from the Atmosphere Model Intercomparison Project (AMIP) of the 5th Coupled Model Intercomparison Project (CMIP5). This study confirms that the low‐cloud optical depth response is timescale invariant in the AMIP simulations, generally at latitudes higher than 40°. Compared to satellite estimates, most models overestimate the increase in optical depth with warming at the monthly and interannual timescales. Many models also do not capture the increase in optical depth with estimated inversion strength that is found in all three satellite observations and in previous studies. The discrepancy between models and satellites exists in both hemispheres and in most months of the year. A simple replacement of the models' optical depth sensitivities with the satellites' sensitivities reduces the negative shortwave cloud feedback by at least 50% in the 40°–70°S latitude band and by at least 65% in the 40°–70°N latitude band. Based on this analysis of satellite observations, we conclude that the low‐cloud optical depth feedback at middle and high latitudes is likely too negative in climate models.

Carbon monoxide climatology derived from the trajectory mapping of global MOZAIC-IAGOS data

Abstract. A three-dimensional gridded climatology of carbon monoxide (CO) has been developed by trajectory mapping of global MOZAIC-IAGOS in situ measurements from commercial aircraft data. CO measurements made during aircraft ascent and descent, comprising nearly 41 200 profiles at 148 airports worldwide from December 2001 to December 2012, are used. Forward and backward trajectories are calculated from meteorological reanalysis data in order to map the CO measurements to other locations and so to fill in the spatial domain. This domain-filling technique employs 15 800 000 calculated trajectories to map otherwise sparse MOZAIC-IAGOS data into a quasi-global field. The resulting trajectory-mapped CO data set is archived monthly from 2001 to 2012 on a grid of 5° longitude × 5° latitude × 1 km altitude, from the surface to 14 km altitude.The mapping product has been carefully evaluated, firstly by comparing maps constructed using only forward trajectories and using only backward trajectories. The two methods show similar global CO distribution patterns. The magnitude of their differences is most commonly 10 % or less and found to be less than 30 % for almost all cases. Secondly, the method has been validated by comparing profiles for individual airports with those produced by the mapping method when data from that site are excluded. While there are larger differences below 2 km, the two methods agree very well between 2 and 10 km with the magnitude of biases within 20 %. Finally, the mapping product is compared with global MOZAIC-IAGOS cruise-level data, which were not included in the trajectory-mapped data set, and with independent data from the NOAA aircraft flask sampling program. The trajectory-mapped MOZAIC-IAGOS CO values show generally good agreement with both independent data sets.Maps are also compared with version 6 data from the Measurements Of Pollution In The Troposphere (MOPITT) satellite instrument. Both data sets clearly show major regional CO sources such as biomass burning in Central and southern Africa and anthropogenic emissions in eastern China. While the maps show similar features and patterns, and relative biases are small in the lowermost troposphere, we find differences of ∼ 20 % in CO volume mixing ratios between 500 and 300 hPa. These upper-tropospheric biases are not related to the mapping procedure, as almost identical differences are found with the original in situ MOZAIC-IAGOS data. The total CO trajectory-mapped MOZAIC-IAGOS column is also higher than the MOPITT CO total column by 12–16 %.The data set shows the seasonal CO cycle over different latitude bands and altitude ranges as well as long-term trends over different latitude bands. We observe a decline in CO over the northern hemispheric extratropics and the tropics consistent with that reported by previous studies using other data sources.We anticipate use of the trajectory-mapped MOZAIC-IAGOS CO data set as an a priori climatology for satellite retrieval and for air quality model validation and initialization.

Climate zones on Pluto and Charon

We give an explanatory description of the unusual “climate zones” on Pluto that arise from its high obliquity (mean 115°) and high amplitude (±12°) of obliquity oscillation over a 2.8 million year period. The zones we describe have astronomically defined boundaries and do not incorporate atmospheric circulation. For such a high mean obliquity, the lines of tropics (greatest latitudes where the Sun can be overhead) cycle closer to each pole than does each arctic circle, which in turn cycle nearly to the equator. As a consequence in an astronomical context, Pluto is more predominantly “tropical” than “arctic.” Up to 97% of Pluto's surface area can experience overhead Sun when the obliquity cycle is at its minimum of 103°. At this same obliquity phase (most recently occurring 0.8Myr ago), 78% of Pluto's surface experienced prolonged intervals without sunlight or “arctic winter” (and corresponding “arctic summer”). The intersection of these climate zones implies that a very broad range of Pluto's latitudes (spanning 13–77° in each hemisphere; 75% of the total surface area) are both tropical and arctic. While some possible correlations to these climate zones are suggested by comparison with published maps of Pluto and Charon yielded by the New Horizons mission, in this work we present a non-physical descriptive analysis only. For example, the planet-wide dark equatorial band presented by Stern et al. (2015; Science, 350, 292–299) corresponds to Pluto's permanent “diurnal zone.” In this zone spanning latitudes within ±13° of the equator, day-night cycles occur each Pluto rotation (6.4 days) such that neither “arctic winter” nor “arctic summer” has been experienced in this zone for at least 20 million years. The stability of this and other climate zones may extend over several Gyr. Temperature modeling shows that the continuity of diurnal cycles in this region may be the key factor enabling a long-term stability for the high albedo contrast between Tombaugh Regio adjacent to the dark Cthulhu Regio (Earle et al. (2017) Icarus, special issue, submitted). (All names are informal.) Charon's synchronous alignment with Pluto dictates that both bodies in the binary pair have the same climate zone structure, but any effects on Charon's morphology may be limited if volatile transport there is minimal or absent. Cold-trapped methane-rich volatiles on top of its water ice surface may be responsible for forming Charon's dark red north polar cap (Grundy et al., 2016b), and we note the most concentrated area of this feature resides almost entirely within the permanent “polar zone” (above 77° latitude) where the Sun never reaches the overhead point and arctic seasons have been most consistently experienced over at least tens of millions of years. Pluto is not alone among bodies in the Kuiper belt (and uranian satellites) in having high obliquities, overlapping tropical and arctic zones, and latitude bands that remain in a continuous diurnal cycle over long terms.

Properties of sunspot cycles and hemispheric wings since the 19th century

Aims. The latitudinal evolution of sunspot emergence over the course of the solar cycle, the so-called butterfly diagram, is a fundamental property of the solar dynamo. Here we present a study of the butterfly diagram of sunspot group occurrence for cycles 7–10 and 11–23 using data from a recently digitized sunspot drawings by Samuel Heinrich Schwabe in 1825–1867, and from RGO/USAF/NOAA(SOON) compilation of sunspot groups in 1874–2015.Methods. We developed a new, robust method of hemispheric wing separation based on an analysis of long gaps in sunspot group occurrence in different latitude bands. The method makes it possible to ascribe each sunspot group to a certain wing (solar cycle and hemisphere), and separate the old and new cycle during their overlap. This allows for an improved study of solar cycles compared to the common way of separating the cycles.Results. We separated each hemispheric wing of the butterfly diagram and analysed them with respect to the number of groups appearing in each wing, their lengths, hemispheric differences, and overlaps.Conclusions. The overlaps of successive wings were found to be systematically longer in the northern hemisphere for cycles 7–10, but in the southern hemisphere for cycles 16–22. The occurrence of sunspot groups depicts a systematic long-term variation between the two hemispheres. During Schwabe time, the hemispheric asymmetry was north-dominated during cycle 9 and south-dominated during cycle 10.

Persistent longitudinal variations in 8 years of CIPS/AIM polar mesospheric clouds

AbstractThe Cloud Imaging and Particle Size (CIPS) instrument on the Aeronomy of Ice in the Mesosphere (AIM) satellite provides an opportunity to study the longitudinal variation in polar mesospheric cloud (PMC). We examined the longitudinal variation in PMC albedo using 8 years (2007–2014) of observations from the CIPS instrument. The results show that the PMC albedo in the Southern Hemisphere (SH), especially in the latitude band of 80°S–85°S, is persistently low (~65% relative to the rest of the hemisphere) within 60°W to 150°W longitude. In the Northern Hemisphere (NH), however, PMC albedo is found to be relatively zonally asymmetry. Harmonic analyses show that the persistent longitudinal variation in the SH PMC albedo is due to zonal wave numbers 1 through 4 (WN1–WN4) processes with minima in the longitude range of 60°W–150°W. The influence of temperature and H2O on the longitudinal variation of the PMC albedo is discussed based on results obtained using a simple 0‐D PMC model and temperature from the Microwave Limb Sounder (MLS) and the Sounding of the Atmosphere with Broadband Emission Radiometry (SABER) and H2O from MLS. The modeled region of low ice mass in the SH is generally consistent with that of low PMC albedo seen in CIPS. Tidal analyses using the SABER temperatures indicate that the nonmigrating semidiurnal tides with modes of S0, W1, and E1 might be the main drivers of the persistent longitudinal variations of PMC albedo in the SH. Nonmigrating tides are much weaker in the NH and consistent with the observed lack of longitudinal variability in PMC albedo.

Regional and seasonal stratospheric temperature trends in the last decade (2002–2014) from AMSU observations

AbstractStratospheric temperature trends for the period 2002–2014 have been estimated using NOAA's Integrated Microwave Inter‐calibration Approach (IMICA) version of advanced microwave sounding unit (AMSU) on AQUA satellite. In this period the stratosphere continued cooling over most of the globe with a rate ranging from −0.4 ± 0.3 to −0.5 ± 0.4 K/decade above 25 km. Considering specific latitude bands, trends are highly variable with height. In the tropical region, trends vary from −0.5 ± 0.3 K/decade for channel 12 (∼30 km) to −0.7 ± 0.3 K/decade for higher channels and present small seasonal variability in the intensity of cooling. In the polar regions and in the midlatitudes, trends for all channels are negative but not significant; uncertainties are large due to the high dynamical variability particularly in high latitudes. There is also large seasonal variability, with southern midlatitudes seasonal trends significant during summer (December, January, February) and autumn (March, April, May) above ∼25 km, with values ranging from −1.0 ± 0.5 to −0.6 ± 0.5 K/decade. Regional trends estimated with AMSU and long‐term lidar measurements (over two decades) confirm stratospheric cooling in the northern midlatitudes and tropical regions. The effect of the length of the short series on trends was found to be small outside polar regions. It was found to be large in polar regions with about 1 K changes in trend depending on start dates of the time series.

Assessing the Efficacy of High-Resolution Satellite-Based PERSIANN-CDR Precipitation Product in Simulating Streamflow

AbstractThis study aims to investigate the performance of Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks–Climate Data Record (PERSIANN-CDR) in a rainfall–runoff modeling application over the past three decades. PERSIANN-CDR provides precipitation data at daily and 0.25° temporal and spatial resolutions from 1983 to present for the 60°S–60°N latitude band and 0°–360° longitude. The study is conducted in two phases over three test basins from the Distributed Hydrologic Model Intercomparison Project, phase 2 (DMIP2). In phase 1, a more recent period of time (2003–10) when other high-resolution satellite-based precipitation products are available is chosen. Precipitation evaluation analysis, conducted against stage IV gauge-adjusted radar data, shows that PERSIANN-CDR and TRMM Multisatellite Precipitation Analysis (TMPA) have close performances with a higher correlation coefficient for TMPA (~0.8 vs 0.75 for PERSIANN-CDR) and almost the same root-mean-square deviation (~6) for both products. TMPA and PERSIANN-CDR outperform PERSIANN, mainly because, unlike PERSIANN, TMPA and PERSIANN-CDR are gauge-adjusted precipitation products. The National Weather Service Office of Hydrologic Development Hydrology Laboratory Research Distributed Hydrologic Model (HL-RDHM) is then forced with PERSIANN, PERSIANN-CDR, TMPA, and stage IV data. Quantitative analysis using five different statistical and model efficiency measures against USGS streamflow observation show that in general in all three DMIP2 basins, the simulated hydrographs forced with PERSIANN-CDR and TMPA have close agreement. Given the promising results in the first phase, the simulation process is extended back to 1983 where only PERSIANN-CDR rainfall estimates are available. The results show that PERSIANN-CDR-derived streamflow simulations are comparable to USGS observations with correlation coefficients of ~0.67–0.73, relatively low biases (~5%–12%), and high index of agreement criterion (~0.68–0.83) between PERSIANN-CDR-simulated daily streamflow and USGS daily observations. The results prove the capability of PERSIANN-CDR in hydrological rainfall–runoff modeling application, especially for long-term streamflow simulations over the past three decades.

Estudo do Fenômeno da Ilha de Calor na Cidade de Manaus/AM: Um Estudo a Partir de Dados de Sensoriamento Remoto, Modelagem e Estações Meteorológicas

Resumo O fenômeno da ilha de calor (IC) na cidade de Manaus foi estudado usando dados de modelagem do clima urbano com o modelo Weather Research and Forecasting (WRF) e dados de estações meteorológicas. Foram usados os dados de temperatura da superfície (TS) obtidos pelo sensor MODIS do satélite ambiental Aqua, produto MYD11A2 na resolução horizontal de 1 km por um 1 km para o período de 2002 a 2012 na cidade de Manaus para avaliar o processo de urbanização. Foi realizado um estudo de caso com as simulações de TS e de temperatura do ar (TA) nos meses de agosto e setembro de 2009 que foram comparadas, respectivamente, com os dados de satélite e de estações meteorológicas. Identificou-se a distribuição espacial da TS na cidade, e as diferenças de TS entre a área urbana e a de floresta e entre a área urbana e de rios foram quantificadas. As diferenças de TS ao longo das faixas de longitude de 60,03° O a 59,97° O e de latitude de 3,09° S a −3,03° S foram analisadas com os dados do modelo WRF e do sensor MODIS. A intensidade da IC estimada com os dados de TA do modelo e de estações meteorológicas foram, em média, respectivamente de 1,87 °C e de 1,80 °C, consistentes com resultados anteriores. Portanto, a TA simulada pode ser usada para fins de estimar a intensidade da IC em Manaus.

A mathematical framework for analysis of water tracers: Part 1: Development of theory and application to the preindustrial mean state

AbstractA new matrix operator framework is developed to analyze results from climate modeling studies that employ numerical water tracers (WTs), which track the movement of water in the aerial hydrological cycle from evaporation to precipitation. Model WT output is related to the fundamental equation of hydrology, and the moisture flux divergence is subdivided into the divergence of locally evaporated moisture and the convergence of remotely evaporated moisture. The formulation also separates locally and remotely sourced precipitation. The remote contribution (also the remote moisture convergence) may be further subdivided into zonal, meridional, intrabasin, and interbasin parts. This framework is applied to the preindustrial climate as simulated by a global climate model in which water has been tagged in 10° latitude bands in each of the major ocean basins, and in which each major land mass has been tagged separately. New insights from the method reveal fundamental differences between the major ocean basins in locally sourced precipitation, remotely sourced precipitation, and their relative partitioning. Per unit area, the subtropical Atlantic is the largest global moisture source, providing precipitable water to adjacent land areas and to the eastern Pacific tropics while retaining the least for in situ precipitation. Subtropical moisture is least divergent over the Pacific, which is the smallest moisture source (per unit area) for global land areas. Basins also differ in how subtropical moisture is partitioned between tropical, midlatitude, and land regions. Part II will apply this framework to hydrological cycle perturbations due to CO2 doubling.

Stratospheric gravity wave momentum flux from radio occultations

AbstractTriples of GPS radio occultation (RO) temperature data are used to derive horizontal and vertical gravity wave (GW) parameters in the stratosphere between 20 km and 40 km from which the vertical flux of horizontal momentum is determined. Compared to previous studies using RO data, better limiting values for the sampling distance (Δd≤250 km) and the time interval (Δt≤15 min) are used. For several latitude bands the mean momentum fluxes (MFs) derived in this study are considerably larger than MF from other satellite missions based on horizontal wavelengths calculated between two adjacent temperature profiles along the satellite track. Error sources for the estimation of MF from RO data and the geometrical setup for the applied method are investigated. Another crucial issue discussed in this paper is the influence of different background separation methods to the final MF. For GW analysis a measured temperature profile is divided into a fluctuation and a background and it is assumed that the fluctuation is caused by GWs only. For the background separation, i.e., the detrending of large‐scale processes from the measured temperature profile, several methods exist. In this study we compare different detrending approaches and for the first time an attempt is made to detrend RO data with ERA‐Interim data from the European Centre for Medium‐Range Weather Forecasts. We demonstrate that the horizontal detrending based on RO data and ERA‐Interim gives more consistent results compared with a vertical detrending.

Retrieving Neptune’s aerosol properties from Keck OSIRIS observations. I. Dark regions

We present and analyze three-dimensional data cubes of Neptune from the OSIRIS integral-field spectrograph on the 10-m W.M. Keck II telescope, from 26 July 2009. These data have a spatial resolution of 0.035/pixel and spectral resolution of R ∼3800 in the H (1.47–1.80 µm) and K (1.97–2.38 µm) broad bands. We focus our analysis on regions of Neptune’s atmosphere that are near-infrared dark – that is, free of discrete bright cloud features. We use a forward model coupled to a Markov chain Monte Carlo algorithm to retrieve properties of Neptune’s aerosol structure and methane profile above ∼4 bar in these near-infrared dark regions.We construct a set of high signal-to-noise spectra spanning a range of viewing geometries to constrain the vertical structure of Neptune’s aerosols in a cloud-free latitude band from 2–12°N. We find that Neptune’s cloud opacity at these wavelengths is dominated by a compact, optically thick cloud layer with a base near 3 bar. Using the pyDISORT algorithm for the radiative transfer and assuming a Henyey-Greenstein phase function, we observe this cloud to be composed of low albedo (single scattering albedo =0.45−0.01+0.01), forward scattering (asymmetry parameter g=0.50−0.02+0.02) particles, with an assumed characteristic size of ∼1µm. Above this cloud, we require an aerosol layer of smaller (∼0.1µm) particles forming a vertically extended haze, which reaches from the upper troposphere (0.59−0.03+0.04 bar) into the stratosphere. The particles in this haze are brighter (single scattering albedo =0.91−0.05+0.06) and more isotropically scattering (asymmetry parameter g=0.24−0.03+0.02) than those in the deep cloud. When we extend our analysis to 18 cloud-free locations from 20°N to 87°S, we observe that the optical depth in aerosols above 0.5 bar decreases by a factor of 2–3 or more at mid- and high-southern latitudes relative to low latitudes.We also consider Neptune’s methane (CH4) profile, and find that our retrievals indicate a strong preference for a low methane relative humidity at pressures where methane is expected to condense. When we include in our fits a parameter for methane depletion below the CH4 condensation pressure, our preferred solution at most locations is for a methane relative humidity below 10% near the tropopause in addition to methane depletion down to 2.0–2.5 bar. We tentatively identify a trend of lower CH4 columns above 2.5 bar at mid- and high-southern latitudes over low latitudes, qualitatively consistent with what is found by Karkoschka and Tomasko (2011), and similar to, but weaker than, the trend observed for Uranus.

Deforestation Induced Climate Change: Effects of Spatial Scale.

Deforestation is associated with increased atmospheric CO2 and alterations to the surface energy and mass balances that can lead to local and global climate changes. Previous modelling studies show that the global surface air temperature (SAT) response to deforestation depends on latitude, with most simulations showing that high latitude deforestation results in cooling, low latitude deforestation causes warming and that the mid latitude response is mixed. These earlier conclusions are based on simulated large scal land cover change, with complete removal of trees from whole latitude bands. Using a global climate model we examine the effects of removing fractions of 5% to 100% of forested areas in the high, mid and low latitudes. All high latitude deforestation scenarios reduce mean global SAT, the opposite occurring for low latitude deforestation, although a decrease in SAT is simulated over low latitude deforested areas. Mid latitude SAT response is mixed. In all simulations deforested areas tend to become drier and have lower SAT, although soil temperatures increase over deforested mid and low latitude grid cells. For high latitude deforestation fractions of 45% and above, larger net primary productivity, in conjunction with colder and drier conditions after deforestation cause an increase in soil carbon large enough to produce a net decrease of atmospheric CO2. Our results reveal the complex interactions between soil carbon dynamics and other climate subsystems in the energy partition responses to land cover change.

Seasonal responses of terrestrial ecosystem water-use efficiency to climate change.

Ecosystem water-use efficiency (EWUE) is an indicator of carbon-water interactions and is defined as the ratio of carbon assimilation (GPP) to evapotranspiration (ET). Previous research suggests an increasing long-term trend in annual EWUE over many regions and is largely attributed to the physiological effects of rising CO2 . The seasonal trends in EWUE, however, have not yet been analyzed. In this study, we investigate seasonal EWUE trends and responses to various drivers during 1982-2008. The seasonal cycle for two variants of EWUE, water-use efficiency (WUE, GPP/ET), and transpiration-based WUE (WUEt , the ratio of GPP and transpiration), is analyzed from 0.5° gridded fields from four process-based models and satellite-based products, as well as a network of 63 local flux tower observations. WUE derived from flux tower observations shows moderate seasonal variation for most latitude bands, which is in agreement with satellite-based products. In contrast, the seasonal EWUE trends are not well captured by the same satellite-based products. Trend analysis, based on process-model factorial simulations separating effects of climate, CO2 , and nitrogen deposition (NDEP), further suggests that the seasonal EWUE trends are mainly associated with seasonal trends of climate, whereas CO2 and NDEP do not show obvious seasonal difference in EWUE trends. About 66% grid cells show positive annual WUE trends, mainly over mid- and high northern latitudes. In these regions, spring climate change has amplified the effect of CO2 in increasing WUE by more than 0.005gCm(-2) mm(-1) yr(-1) for 41% pixels. Multiple regression analysis further shows that the increase in springtime WUE in the northern hemisphere is the result of GPP increasing faster than ET because of the higher temperature sensitivity of GPP relative to ET. The partitioning of annual EWUE to seasonal components provides new insight into the relative sensitivities of GPP and ET to climate, CO2, and NDEP.

Climate change induced by Southern Hemisphere desertification

Some 10–20% of global dry-lands are already degraded, and the ongoing desertification threatens the world's poorest populations. Studies on desertification effects are essential for humans to adapt to the environmental challenges posed by desertification. Given the importance of the much larger southern ocean to the global climate and the Southern Hemisphere (SH) climate changes in phase with those in the north, the biogeophysical effects of the SH desertification on climate are assessed using an Earth system model of intermediate complexity, MPM-2. This analysis focuses on differences in climate among the averages of simulations with desert expansion in different latitude bands by year 2000. The localized desertification causes significant global changes in temperature and precipitation as well as surface albedo. On the global scale, cooling dominates the SH desertification effects. However, the biogeophysical effects are most significant in regions with desertification, and the cooling is also prominent in northern mid-latitudes. Desert expansion in 15°–30°S reveals statistically most significant cooling and increased precipitation over the forcing regions during spring. The global and regional scale responses from desertification imply the climate teleconnection and address the importance of the effects from the SH which are contingent on the location of the forcing. Our study indicates that biogeophysical mechanisms of land cover changes in the SH need to be accounted for in the assessment of land management options especially for latitude band over 15°-30°S.

Factors associated with photoprotection by body clothing coverage, particularly in non-summer months, among a New Zealand community sample.

Clothing coverage is important for reducing skin cancer risk, but may also influence vitamin D sufficiency, so associated plausible predictors require investigation. Volunteers (18 to 85 years), with approximately equal numbers by sex and four ethnicity groups, were recruited in cities from two latitude bands: Auckland (36.9°S) and Dunedin (45.9°S). Baseline questionnaire, anthropometric and spectrophotometer skin colour data were collected and weather data obtained. Percent body coverage was calculated from eight week diary records. Potential independent predictors (unadjusted p < 0.25) were included in adjusted models. Participants (n = 506: Auckland n = 334, Dunedin n = 172; mean age 48.4 years) were 62.7% female and had a median body clothing coverage of 81.6% (IQR 9.3%). Dunedin was cooler, less windy and had lower UVI levels than Auckland. From the fully adjusted model, increased coverage occurred in non-summer months (despite adjusting for weather), among Dunedin residents and Asians (compared to Europeans), during the middle of the day, with a dose response effect observed for greater age. Reduced coverage was associated with Pacific ethnicity and greater time spent outdoors. Additionally, higher temperatures were associated with reduced coverage, whereas increased cloud cover and wind speed were associated with increased coverage. Although the only potentially modifiable factors associated with clothing coverage were the time period and time spent outdoors, knowledge of these and other associated factors is useful for the framing and targeting of health promotion messages to potentially influence clothing coverage, facilitate erythema avoidance and maintain vitamin D sufficiency.

An objective classification of Saturn cloud features from Cassini ISS images

A k-means clustering algorithm is applied to Cassini Imaging Science Subsystem continuum and methane band images of Saturn's northern hemisphere to objectively classify regional albedo features and aid in their dynamical interpretation. The procedure is based on a technique applied previously to visible-infrared images of Earth. It provides a new perspective on giant planet cloud morphology and its relationship to the dynamics and a meteorological context for the analysis of other types of simultaneous Saturn observations. The method identifies 6 clusters that exhibit distinct morphology, vertical structure, and preferred latitudes of occurrence. These correspond to areas dominated by deep convective cells; low contrast areas, some including thinner and thicker clouds possibly associated with baroclinic instability; regions with possible isolated thin cirrus clouds; darker areas due to thinner low level clouds or clearer skies due to downwelling, or due to absorbing particles; and fields of relatively shallow cumulus clouds. The spatial associations among these cloud types suggest that dynamically, there are three distinct types of latitude bands on Saturn: deep convectively disturbed latitudes in cyclonic shear regions poleward of the eastward jets; convectively suppressed regions near and surrounding the westward jets; and baroclinically unstable latitudes near eastward jet cores and in the anti-cyclonic regions equatorward of them. These are roughly analogous to some of the features of Earth's tropics, subtropics, and midlatitudes, respectively. This classification may be more useful for dynamics purposes than the traditional belt-zone partitioning. Temporal variations of feature contrast and cluster occurrence suggest that the upper tropospheric haze in the northern hemisphere may have thickened by 2014. The results suggest that routine use of clustering may be a worthwhile complement to many different types of planetary atmospheric data analysis.

Sensitivity Study on the Influence of Cloud Microphysical Parameters on Mixed-Phase Cloud Thermodynamic Phase Partitioning in CAM5

Abstract The influence of six CAM5.1 cloud microphysical parameters on the variance of phase partitioning in mixed-phase clouds is determined by application of a variance-based sensitivity analysis. The sensitivity analysis is based on a generalized linear model that assumes a polynomial relationship between the six parameters and the two-way interactions between them. The parameters, bounded such that they yield realistic cloud phase values, were selected by adopting a quasi–Monte Carlo sampling approach. The sensitivity analysis is applied globally, and to 20°-latitude-wide bands, and over the Southern Ocean at various mixed-phase cloud isotherms and reveals that the Wegener–Bergeron–Findeisen (WBF) time scale for the growth of ice crystals single-handedly accounts for the vast majority of the variance in cloud phase partitioning in mixed-phase clouds, while its interaction with the WBF time scale for the growth of snowflakes plays a secondary role. The fraction of dust aerosols active as ice nuclei in latitude bands, and the parameter related to the ice crystal fall speed and their interactions with the WBF time scale for ice are also significant. All other investigated parameters and their interactions with each other are negligible (&amp;lt;3%). Further analysis comparing three of the quasi–Monte Carlo–sampled simulations with spaceborne lidar observations by CALIOP suggests that the WBF process in CAM5.1 is currently parameterized such that it occurs too rapidly due to failure to account for subgrid-scale variability of liquid and ice partitioning in mixed-phase clouds.

The puzzling Venusian polar atmospheric structure reproduced by a general circulation model.

Unlike the polar vortices observed in the Earth, Mars and Titan atmospheres, the observed Venus polar vortex is warmer than the midlatitudes at cloud-top levels (∼65 km). This warm polar vortex is zonally surrounded by a cold latitude band located at ∼60° latitude, which is a unique feature called ‘cold collar' in the Venus atmosphere. Although these structures have been observed in numerous previous observations, the formation mechanism is still unknown. Here we perform numerical simulations of the Venus atmospheric circulation using a general circulation model, and succeed in reproducing these puzzling features in close agreement with the observations. The cold collar and warm polar region are attributed to the residual mean meridional circulation enhanced by the thermal tide. The present results strongly suggest that the thermal tide is crucial for the structure of the Venus upper polar atmosphere at and above cloud levels.

Satellite assessment of sea spray aerosol productivity: Southern Ocean case study

AbstractDespite many years of observations by multiple sensors, there is still substantial ambiguity regarding aerosol optical depths (AOD) over remote oceans, in particular, over the pristine Southern Ocean. Passive satellite retrievals (e.g., Multiangle Imaging Spectroradiometer (MISR) and Moderate Resolution Imaging Spectroradiometer (MODIS)) and global aerosol transport models show a distinct AOD maximum around the 60°S latitude band. Sun photometer measurements performed by the Maritime Aerosol Network (MAN), on the other hand, indicate no increased AODs over the Southern Ocean. In this study elevated Southern Ocean AODs are examined from the modeling perspective. The primary aerosol component over the Southern Ocean is sea spray aerosol (SSA). Multiple simulations of SSA concentrations and optical depths are carried out using a single modeling framework, the Navy Aerosol Analysis and Prediction System (NAAPS) model. Several SSA emission functions are examined, including recently proposed formulations with sea surface temperature corrections. The differences between NAAPS simulations are primarily due to different SSA emission formulations. The results are compared against satellite‐derived AODs from the MISR and MODIS instruments. MISR and MODIS AOD retrievals are further filtered to eliminate retrievals potentially affected by cloud contamination and cloud adjacency effects. The results indicate a very large impact of SSA emission parameterization on the simulated AODs. For some scenarios, the Southern Ocean AOD maximum almost completely disappears. Further MISR and MODIS AOD quality screening substantially improves model/satellite agreement. Based on these comparisons, an optimal SSA emission function for global aerosol transport models is recommended.

Global tropospheric ozone variations from 2003 to 2011 as seen by SCIAMACHY

Abstract. An analysis of the tropospheric ozone (O3) columns (TOCs) derived from SCIAMACHY limb-nadir-matching (LNM) observations during the period 2003–2011, focusing on global variations in TOC, is described. The changes are derived using a multivariate linear regression model. TOC shows changes of −0.2 ± 0.4, 0.3 ± 0.4, 0.1 ± 0.5 and 0.1 ± 0.2 % yr−1, which are not statistically significant at the 2σ level in the latitude bands 30–50° N, 20° S–0, 0–20° N and 50–30° S, respectively. Tropospheric O3 shows statistically significant increases over some regions of South Asia (1–3 % yr−1), the South American continent (up to 2 % yr−1), Alaska (up to 2 % yr−1) and around Congo in Africa (up to 2 % yr−1). Significant increase in TOC is determined off the continents including Australia (up to 2 % yr−1), Eurasia (1–3 % yr−1) and South America (up to 3 % yr−1). Significant decrease in TOC (up to −3 % yr−1) is observed over some regions of the continents of North America, Europe and South America. Over the oceanic regions including the Pacific, North Atlantic and Indian oceans, significant decreases in TOC (−1 to −3 % yr−1) were observed. In addition, the response of the El Niño–Southern Oscillation (ENSO) and quasi-biennial oscillation (QBO) to changes in TOC for the period 2003–2011 was investigated. The result shows extensive regions, mostly in the tropics and Northern Hemisphere extratropics, of significant ENSO responses to changes in TOC and a significant QBO response to TOC changes over some regions.