Diurnal Time Scales Research Articles

The Role of Upper-Level Coupling on Great Plains Low-Level Jet Structure and Variability

AbstractThe Great Plains (GP) southerly nocturnal low-level jet (GPLLJ) is a dominant contributor to the region’s warm-season (May–September) mean and extreme precipitation, wind energy generation, and severe weather outbreaks—including mesoscale convective systems. The spatiotemporal structure, variability, and impact of individual GPLLJ events are closely related to their degree of upper-level synoptic coupling, which varies from strong coupling in synoptic trough–ridge environments to weak coupling in quiescent, synoptic ridge environments. Here, we apply an objective dynamic classification of GPLLJ upper-level coupling and fully characterize strongly coupled (C) and relatively uncoupled (UC) GPLLJs from the perspective of the ground-based observer. Through composite analyses of C and UC GPLLJ event samples taken from the European Centre for Medium-Range Weather Forecasts’ Coupled Earth Reanalysis of the twentieth century (CERA-20C), we address how the frequency of these jet types, as well as their inherent weather- and climate-relevant characteristics—including wind speed, direction, and shear; atmospheric stability; and precipitation—vary on diurnal and monthly time scales across the southern, central, and northern subregions of the GP. It is shown that C and UC GPLLJ events have similar diurnal phasing, but the diurnal amplitude is much greater for UC GPLLJs. C GPLLJs tend to have a faster and more elevated jet nose, less low-level wind shear, and enhanced CAPE and precipitation. UC GPLLJs undergo a larger inertial oscillation (Blackadar mechanism) for all subregions, and C GPLLJs have greater geostrophic forcing (Holton mechanism) in the southern and northern GP. The results underscore the need to differentiate between C and UC GPLLJs in future seasonal forecast and climate prediction activities.

Underwater sound generated by motor vehicle traffic in an underwater tunnel

Underwater acoustic and environmental measurements were made adjacent to the Monitor-Merrimac Memorial Bridge-Tunnel in the James River in Virginia during a field experiment in April 2019. The observed sound field exhibited short time-scale and tidal time-scale variability due to passing marine vessels and tidally driven currents in the estuary; most interestingly, the sound field exhibited variability on a diurnal time scale, closely correlated to the temporal distribution of vehicular traffic in the underwater tunnel. During morning and evening rush-hour traffic periods, the amplitude of the traffic-induced underwater signal exceeded 10 dB at 40 Hz. Additional physics-based modeling and direct observation are required to verify the hypothesis that the signal is associated with the traffic-induced vibration in the tunnel roadbed.

δ18O and δ13C of Cyprideis torosa from coastal lakes: Modern systematics and down-core interpretation

Stable isotope analyses of ostracod shells are a commonly-used proxy for palaeoenvironmental reconstruction. Although the fundamental controls on isotope composition of ostracod shells are well understood and, in some instances, quantifiable, the paleoclimatic and palaeoenvironmental interpretation of records from lake sediments depends strongly on the characteristics of individual lakes including the climatic setting, depth, volume, hydrology, aquatic vegetation and catchment properties. This is particularly important for coastal lakes where physio-chemical variations may occur on diurnal timescales. Here, we combine variations in δ 18 O water , δ 18 O ostracod and δ 13 C ostracod , hourly water temperature, and Mg/Ca ostracod inferred water temperatures (constraining calcification temperature) to improve palaeoenvironmental interpretation and provide insights into lake carbon cycle. The dataset improves understanding of complex coastal lake site systematics and downcore interpretation of stable isotopes from C. torosa , a geographically widespread brackish water ostracod. The δ 18 O ostracod values show a complex relationship with temperature and suggest, in most circumstances, that δ 18 O water is the dominant control on δ 18 O ostracod . During times of fresher water, δ 13 C ostracod increases, suggesting increasing aquatic productivity. Above a certain δ 18 O water threshold however, aquatic productivity begins to decline. The interpretation of δ 13 C ostracod in some coastal lakes, may therefore be dependent on understanding of the range of expected δ 18 O water . Due to short-term (diurnal to seasonal) variations that cause large ranges in δ 18 O water and δ 18 O ostracod , stable isotope analyses of C. torosa should be: (1) undertaken on multiple single shells (2) where carapaces are preserved, paired with trace-element/Ca analyses on the same individual; and (3) undertaken alongside a study of the modern lake system. • In most circumstances, δ 18 O water is the dominant control on δ 18 O ostracod . • δ 13 C ostracod is likely controlled by productivity and the oxidation of terrestrial organic matter. • Samples that show a relationship with temperature have higher δ 18 O and a decreasing trend with δ 13 C. • Only some valves in a palaeo-dataset with mixed seasonal signals may relate to palaeo-temperature.

Attribution of the land surface temperature response to land-use conversions from bare land

Abstract Since the early 1980s, large-scale revegetation has been implemented in Northwest China and has been found to be useful in desertification prevention. However, it remains unclear, how land cover changes affect local meteorological conditions, such as land surface temperature. In this study, the land surface temperature response to land-use changes was comparatively evaluated using micrometeorological observations from a cropland site, a mixed forest site, a shrubland site, and adjacent bare land sites in the Heihe River Basin, Northwest China. The surface temperature changes (ΔTs) are decomposed into contributions from changes in radiative forcing, heat resistance, evapotranspiration, soil heat flux and air temperature based on the intrinsic biophysical mechanism (IBM) and the two-resistance mechanism (TRM). The results indicate that 1) the IBM attribution method is more applicable than the TRM method in these arid ecosystems; 2) the influence of different types of vegetation cover on the surface temperature exhibits temporal variance on the diurnal and seasonal time scales; 3) the dominant biophysical components in the daytime of the growing season are evaporative cooling in the cropland paired sites and heat resistance change in the mixed forest paired sites, but these two components are both at a moderate level in the shrubland paired sites. This study provides a useful reference for local climate impact assessments when implementing environmental protection projects in similarly arid areas.

Long-term variation in CO2 emissions with implications for the interannual trend in PM2.5 over the last decade in Beijing, China

Long-term CO2 and PM2.5 measurements in urban areas have important impacts on understanding the roles of urbanization in climate change and air pollution. From 2009 to 2017, CO2 fluxes were measured by the eddy covariance (EC) system at a height of 140 m on the Beijing Meteorological Tower. The CO2 fluxes followed a typical two-peak diurnal pattern all year round. The PM2.5 concentrations followed a similar diurnal pattern as the CO2 fluxes in summer but a different diurnal pattern in winter (low in the day and high at night). On a seasonal time scale, both the CO2 fluxes and the PM2.5 concentrations showed a pronounced seasonal variation (high in winter and low in summer). The spatial variations in CO2 fluxes were dominated by the prevailing land use types within the flux footprint, particularly dense residential areas and heavy traffic roads. On both diurnal and annual time scales, the urban underlying surface was a net source of CO2. The 9-year average annual total CO2 flux was 36.4 kg CO2·m−2 yr−1. Depending on the yearly prevailing wind direction, the effect of the heterogeneity correction on the annual total CO2 fluxes based on the gap-filled dataset could reach up to 3.5%. Over the 9-year period, both the CO2 fluxes and the PM2.5 concentrations exhibited a declining interannual trend, and CO2 fluxes could account for 64% of the interannual variability in PM2.5 concentrations. In summer, emissions were more likely to control the interannual variability in PM2.5 concentrations, whereas in winter, meteorological conditions had a greater impact on the interannual variability in PM2.5 concentrations.

Parametric strategy on passive design affordances in cool-humid climate zones of North-East India

Buildings often have fixed function spaces that are complimentary or incompatible with thermal comfort (18–28 °C). Synergetic relationships ameliorates energy shortage and affords comfort. Galvanized iron roof two-storey houses of North-East India were studied to develop a theory-and-strategy to optimize design process and energy conservation. Methods include affordance theory criticism, surveys, simulations, synergy analysis. Parametric strategy on passive design affordances examines human comfort and temperature on diurnal time scales: Daytime (08–17 h), Evening (17–22 h), Night (22–08 h) in various seasons. Under flexible ventilation, living-dining space (S1) shows optimum temperature ranges: 20–28 °C in autumn (M1), 17–22 °C in winter (M2), and 20–31 °C in summer (M3) due to the complementary combination of passive design elements and can function as bedroom, living-room, kitchen, and social space in most seasons. In the attic-space flexible ventilation shows peak temperatures of 42 °C (autumn) and 48 °C (summer) due to low thermal mass but high thermal conductivity envelopes, and low air-changes rate (0.5 ACR) above 28 °C. Normal ventilations with 30 ACR in autumn, and a combination of 30 ACR (night) and 0.5 ACR (day) in summer reduced maximum temperature to ≤35 °C in autumn, and ≤41 °C in summer. Attic-space (S2) shows ≤29 °C in winter daytime and ≥20 °C in summer nights due to the envelope’s high heat emissivity (0.8) and function as day space in winter and summer bedroom. Shaded veranda (S3) shows low temperature (18–28 °C) in summer evening and afternoon and can function as shaded space for light work and enjoying fresh air. Passive design connotes responsiveness of spaces to the climate, and affordance theory’s complementarity lifestyle adds novelty, and it is critical to energy and space efficiency. Climate analysis affords perceptions of space and climate relationship. Parametric strategy straddles differences between space, climate, and functions to ameliorate energy needs and optimize design process.

Scientific Observations With the InSight Solar Arrays: Dust, Clouds, and Eclipses on Mars.

Records of solar array currents recorded by the InSight lander during its first 200 sols on Mars are presented. In addition to the geometric variation in illumination on seasonal and diurnal timescales, the data are influenced by dust suspended in the atmosphere and deposited on the solar panels. Although no dust devils have been detected by InSight's cameras, brief excursions in solar array currents suggest that at least some of the vortices detected by transient pressure drops are accompanied by dust. A step increase in array output (i.e., a “cleaning event”) was observed to be directly associated with the passage of a strong vortex. Some quasiperiodic variations in solar array current are suggestive of dust variations in the planetary boundary layer. Nonzero array outputs before sunrise and after sunset are indicative of scattering in the atmosphere: A notable increase in evening twilight currents is observed associated with noctilucent clouds, likely of water or carbon dioxide ice. Finally, although the observations are intermittent (typically a few hours per sol) and at a modest sample rate (one to two samples per minute), three single‐sample light dips are seen associated with Phobos eclipses. These results demonstrate that engineering data from solar arrays provide valuable scientific situational awareness of the Martian environment.

Canopy structure explains the relationship between photosynthesis and sun-induced chlorophyll fluorescence in crops

Remote sensing of far-red sun-induced chlorophyll fluorescence (SIF) has emerged as an important tool for studying gross primary productivity (GPP) at the global scale. However, the relationship between SIF and GPP at the canopy scale lacks a clear mechanistic explanation. This is largely due to the poorly characterized role of the relative contributions from canopy structure and leaf physiology to the variability of the top-of-canopy, observed SIF signal. In particular, the effect of the canopy structure beyond light absorption is that only a fraction (fesc) of the SIF emitted from all leaves in the canopy can escape from the canopy due to the strong scattering of near-infrared radiation. We combined rice, wheat and corn canopy-level in-situ datasets to study how the physiological and structural components of SIF individually relate to measures of photosynthesis. At seasonal time scales, we found a considerably strong positive correlation (R2 = 0.4–0.6) of fesc to the seasonal dynamics of the photosynthetic light use efficiency (LUEP), while the estimated physiological SIF yield was almost entirely uncorrelated to LUEP both at seasonal and diurnal time scales, with the partial exception of wheat. Consistent with these findings, the canopy structure and radiation component of SIF, defined as the product of APAR and fesc, explained the relationship of observed SIF to GPP and even outperformed GPP estimation based on observed SIF at two of the three sites investigated. These results held for both half-hourly and daily mean values. In contrast, the total emitted SIF, obtained by normalizing observed SIF for fesc, improved only the relationship to APAR but considerably decreased the correlation to GPP for all three crops. Our findings demonstrate the dominant role of canopy structure in the SIF-GPP relationship and establish a strong, mechanistic link between the near-infrared reflectance of vegetation (NIRV) and the relevant canopy structure information contained in the SIF signal. These insights are expected to be useful in improving remote sensing based GPP estimates.

Monitoring the differential reflectivity and receiver calibration of the German polarimetric weather radar network

Abstract. It is a challenge to calibrate differential reflectivity ZDR to within 0.1–0.2 dB uncertainty for dual-polarization weather radars that operate 24∕7 throughout the year. During operations, a temperature sensitivity of ZDR larger than 0.2 dB over a temperature range of 10 ∘C has been noted. In order to understand the source of the observed ZDR temperature sensitivity, over 2000 dedicated solar box scans, two-dimensional scans of 5∘ azimuth by 8∘ elevation that encompass the solar disk, were made in 2018 from which horizontal (H) and vertical (V) pseudo antenna patterns are calculated. This assessment is carried out using data from the Hohenpeißenberg research radar which is identical to the 17 operational radar systems of the German Meteorological Service (Deutscher Wetterdienst, DWD). ZDR antenna patterns are calculated from the H and V patterns which reveal that the ZDR bias is temperature dependent, changing about 0.2 dB over a 12 ∘C temperature range. One-point-calibration results, where a test signal is injected into the antenna cross-guide coupler outside the receiver box or into the low-noise amplifiers (LNAs), reveal only a very weak differential temperature sensitivity (<0.02 dB) of the receiver electronics. Thus, the observed temperature sensitivity is attributed to the antenna assembly. This is in agreement with the NCAR (National Center for Atmospheric Research) S-Pol (S-band polarimetric radar) system, where the primary ZDR temperature sensitivity is also related to the antenna assembly (Hubbert, 2017). Solar power measurements from a Canadian calibration observatory are used to compute the antenna gain and to validate the results with the operational DWD monitoring results. The derived gain values agree very well with the gain estimate of the antenna manufacturer. The antenna gain shows a quasi-linear dependence on temperature with different slopes for the H and V channels. There is a 0.6 dB decrease in gain for a 10 ∘C temperature increase, which directly relates to a bias in the radar reflectivity factor Z which has not been not accounted for previously. The operational methods used to monitor and calibrate ZDR for the polarimetric DWD C-band weather radar network are discussed. The prime sources for calibrating and monitoring ZDR are birdbath scans, which are executed every 5 min, and the analysis of solar spikes that occur during operational scanning. Using an automated ZDR calibration procedure on a diurnal timescale, we are able to keep ZDR bias within the target uncertainty of ±0.1 dB. This is demonstrated for data from the DWD radar network comprising over 87 years of cumulative dual-polarization radar operations.

Parameterization of the Surface Energy Balance of a Shallow Water Table Grassland

Extending instantaneous latent heat flux to daily, monthly, or even yearly evapotranspiration (ET) is a fundamental issue in using remote sensing to estimate ET at local and regional scales. In this study, the extending parameterizations of the surface energy balance of a mid-latitude grassland with shallow water table (SWT) at diurnal and seasonal time scales are examined based on data measured by the eddy covariance system and automated weather station from Wageningen University from June 2014 to October 2018. The results show that the ratio of turbulent heat flux to available surface energy (often called budget closure rate) ranges between 0.86 and 0.93 for warm times (March to October), and between 0.59 and 0.77 for cold times (November to February the following year). The parameterization models used to approximate the surface albedo and evaporative fraction (EF) are also evaluated. Although obvious variation under clear skies during daytime are observed, the constant EF and albedo method provided an acceptable estimation of the daily scale ET with an underestimation of about 6–8% for the grassland with SWT and parameterization of diurnal correction shows little improvement in both the bias and RMSE. The progression of daily ET shows a seasonal cycle, which follows the variation of the net radiation flux. These results will be helpful for estimating ET at daily and long temporal scales based on satellite remote sensing.

High-Frequency Radar Observations of Surface Circulation Features along the South-Western Australian Coast

A new merged high-frequency radar (HFR) data set collected using SeaSonde and WERA (WEllen RAdar) systems was used to examine the ocean surface circulation at diurnal, seasonal and inter-annual time scales along the south-west coast of Australia (SWWA), between 29°–32° S. Merging was performed after resampling WERA data on the coarser SeaSonde HFR grid and averaging data from the two HFR systems in the area of common overlap. Direct comparisons between WERA and SeaSonde vectors in their overlapping areas provided scalar and vector correlation values in the range Ru = [0.24, 0.76]; Rv = [0.39, 0.83]; ρ = [0.44, 0.75], with mean bias between velocity components in the range [−0.02, 0.28] ms−1, [−0.16, 0.16] ms−1 for the U, V components, respectively. The lower agreement between vectors was obtained in general at the boundaries of the HFR domains, where the combined effects of the bearing errors, geometrical constraints, and the limited angular field of view were predominant. The combined data set allowed for a novel characterization of the dominant features in the region, such as the warmer poleward-flowing Leeuwin Current (LC), the colder Capes Current (CC) and its northward extensions, the presence of sub-mesoscale to mesoscale eddies and their generation and aggregation areas, along with the extent offshore of the inertial-diurnal signal. The contribution of tides was weak within the entire HFR domain (<10% total variance), whilst signatures of significant inertial- and diurnal-period currents were present due to diurnal–inertial resonance. A clear discontinuity in energy and variance distribution occurred at the shelf break, which separates the continental shelf and deeper offshore regions, and defined the core of the LC. Confined between the LC and the coastline, the narrower and colder CC current was a feature during the summer months. Persistent (lifespan greater than 1 day) sub-mesoscale eddies (Rossby number O (1)) were observed at two main regions, north and south of 31.5° S, offshore of the 200 m depth contour. The majority of these eddies had diameters in the range 10–20 km with 50% more counter clockwise rotating (CCW) eddies compared to clockwise (CW) rotating eddies. The northern region was dominated by CCW eddies that were present throughout the year whilst CW eddies were prevalent in the south with lower numbers during the summer months.

Phase inconsistency as a major source of error in NGFS forecast

South Asian monsoon exhibits multiscale spatiotemporal variability. Analyzing the nature and behavior of numerical weather forecast error associated with these space-time heterogeneities will eventually help in improving the models. We investigate the spatiotemporal error characteristics of the National Centre for Medium-Range Weather Forecasting (NCMRWF) Global Forecast System (NGFS) model over South Asian land and ocean separately. Although error grows with lead-time, it saturates within 3–5 days of forecast initiation. The saturated error is only about 15–25% higher than that of day-1, indicating that most of the error accumulates within first 24-h of forecast. Increase in error over oceanic regions is due to an increase in the area with high error at all precipitation ranges with large day-to-day variability. However, over land error growth is primarily confined at locations of high mean precipitation. Decomposition of error arising due to intensity and phase variations reveals that about 90% of it arises from the model’s inability to capture phase of precipitation at various timescales. We show that NGFS cannot capture synoptic scale variations ($$<10$$ day) after day-2. Both the high-frequency (10–20 day) and low-frequency (30–60 day) intraseasonal variations are reasonably predicted up to day-3. At diurnal timescale, NGFS forecasts show a peak in precipitation about 3–6 h prior to that observed, both over land and ocean. Surprisingly, this error does not change with lead-time. Lastly, we show that major error characteristics do not depend on the seasonal mean monsoon rainfall.

Diurnal cycle of rainfall over Lake Victoria Basin during the long‐rain season based on TRMM satellite estimate

AbstractThe spatial–temporal characteristics of March–April–May rainfall are investigated over Lake Victoria Basin on a diurnal time scale using harmonic and principal component analyses. The study uses high‐resolution Tropical Rainfall Measuring Mission 3B42 V7 satellite estimate for the years 1998–2015. The diurnal signal in the initiation time for the land and the lake shows a difference in amplitude and phase with a peak in the late afternoon to evening over the land and late night to early morning over the lake. The rainfall maximum first appears over the highlands on the northeast of the lake around 1500 local standard time (LST) then intensifies and migrates westwards. Around 0300 LST the rainfall is observed ubiquitously over the lake before localizing in the western half of the lake around 1100 LST. There exists an enhanced rainfall amplitude of about 50% of the daily rainfall mean over the northeastern sector of the basin and the western half of the lake. By comparison, the amplitude of the semi‐diurnal cycle is weaker and in the range of 1–30% of the daily mean. Rainfall amount (RA) values are higher over the lake and the highlands on the east of the basin while lower on southeastern and western parts of the basin. The distribution of RA, rainfall intensity (RI) and rainfall frequency revealed high peak of RA over the eastern part of the basin that may be attributed to the high incidence of moderate rainfall. The peak over the western half of the lake may be ascribed to the enhanced RI over the lake.

Negative Effects of Diurnal Changes in Acidification and Hypoxia on Early-Life Stage Estuarine Fishes

Estuaries serve as important nursery habitats for various species of early-life stage fish, but can experience cooccurring acidification and hypoxia that can vary diurnally in intensity. This study examines the effects of acidification (pH 7.2–7.4) and hypoxia (dissolved oxygen (DO) ~ 2–4 mg L−1) as individual and combined stressors on four fitness metrics for three species of forage fish endemic to the U.S. East Coast: Menidia menidia, Menidia beryllina, and Cyprinodon variegatus. Additionally, the impacts of various durations of exposure to these two stressors was also assessed to explore the sensitivity threshold for larval fishes under environmentally-representative conditions. C. variegatus was resistant to chronic low pH, while M. menidia and M. beryllina experienced significantly reduced survival and hatch time, respectively. Exposure to hypoxia resulted in reduced hatch success of both Menidia species, as well as diminished survival of M. beryllina larvae. Diurnal exposure to low pH and low DO for 4 or 8 h did not alter survival of M. beryllina, although 8 or 12 h of daily exposure through the 10 days posthatch significantly depressed larval size. In contrast, M. menidia experienced significant declines in survival for all intervals of diel cycling hypoxia and acidification (4–12 h). Exposure to 12-h diurnal hypoxia generally elicited negative effects equal to, or of greater severity, than chronic exposure to low DO at the same levels despite significantly higher mean DO exposure concentrations. This evidences a substantial biological cost to adapting to changing DO levels, and implicates diurnal cycling of DO as a significant threat to fish larvae in estuaries. Larval responses to hypoxia, and to a lesser extent acidification, in this study on both continuous and diurnal timescales indicate that estuarine conditions throughout the spawning and postspawn periods could adversely affect stocks of these fish, with diverse implications for the remainder of the food web.

Effects of Dry Deposition on Surface Ozone over South Asia Inferred from a Regional Chemical Transport Model

Dry deposition is a major sink for tropospheric ozone; nevertheless, studies on its effects on ozone distribution are very limited over the rapidly developing South Asian region. We performed numerical simulations using the regional model WRF-Chem (Weather Research and Forecasting Model coupled with chemistry) to investigate the effect of dry deposition on surface ozone over this region by switching dry deposition ON–OFF in the model. Dry deposition of ozone is found to reduce ozone mixing ratios by up to ∼40% over the Indo-Gangetic Plain (IGP) and parts of western and central India. Additional enhancements (by up to ∼5 ppbv) in ozone are simulated when dry deposition for all gaseous species is switched off. We find a significant contrast on the effects of dry deposition from station to station as well as on the diurnal timescales over this region. The enhancements in ozone, caused by the absence of dry deposition, are lower over urban stations during nighttime, as compared to the rural and high-altitude stations. Significant enhancements in ozone levels in the absence of dry deposition over the mostly agrarian IGP underpin the importance of dry deposition particularly in the vegetated areas. The South Asian ecosystem is seen to act as an important sink of surface ozone via the dry deposition. The analyses partially fill a gap in the studies of dry deposition over the South Asian region, where this sink is anticipated to get perturbed following the changes in land use and land cover.

Assessment of leaf water enrichment of Platycladus orientalis using numerical modeling with different isotopic models

Abstract Investigation of leaf water enrichment may improve our understanding of evapotranspiration partitioning and material exchange between the inside and the outside of leaves. In this study, with measurements of diel variations in δ18O of bulk leaf water (δL,b) of Platycladus orientalis, two theories (the Peclet effect and the two-pool model) describing leaf water enrichment were assessed. The proportional difference between observed and modeled leaf water enrichment, f, was estimated using both isotopic-steady-state (ISS) and non-steady-state (NSS) models to test the two theories. The results showed that differences between ISS- and NSS-modeled leaf water enrichment at the evaporative sites (Δl,e) were not significant (p > 0.05), thus estimated f was not significantly (p > 0.05) influenced by assuming ISS or NSS conditions. Under both ISS and NSS conditions, no significant (P > 0.05) positive f–Tr (leaf transpiration rate) relationships were found on either diel or diurnal time scales, indicating that the Peclet effect is not required to describe bulk leaf water enrichment. Therefore, it would be adequate to combine the simple two-pool model with the ISS model to predict δ18O of bulk leaf water of P. orientalis. These results may have implications for parameterizing the carbon cycle, past climates, and evapotranspiration partitioning models.

First Provisional Land Surface Reflectance Product from Geostationary Satellite Himawari-8 AHI

A provisional surface reflectance (SR) product from the Advanced Himawari Imager (AHI) on-board the new generation geostationary satellite (Himawari-8) covering the period between July 2015 and December 2018 is made available to the scientific community. The Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm is used in conjunction with time series Himawari-8 AHI observations to generate 1-km gridded and tiled land SR every 10 minutes during day time. This Himawari-8 AHI SR product includes retrieved atmospheric properties (e.g., aerosol optical depth at 0.47µm and 0.51µm), spectral surface reflectance (AHI bands 1–6), parameters of the RTLS BRDF model, and quality assurance flags. Product evaluation shows that Himawari-8 AHI data on average yielded 35% more cloud-free, valid pixels in a single day when compared to available data from the low earth orbit (LEO) satellites Terra/Aqua with MODIS sensor. Comparisons of Himawari-8 AHI SR against corresponding MODIS SR products (MCD19A1) over a variety of land cover types with the similar viewing geometry show high consistency between them, with correlation coefficients (r) being 0.94 and 0.99 for red and NIR bands, respectively. The high-frequency geostationary data are expected to facilitate studies of ecosystems on daily to diurnal time scales, complementing observations from networks such as the FLUXNET.

Downwelling Events in a Coastal Mussel Farming Area, NW Thessaloniki’s Gulf (NW Aegean Sea)

The coastal area of Chalastra (NW Thessaloniki’s Gulf, Northern Greece) features prominent mussel farming activity as well as fishing activity. These activities are closely related to the hydrodynamics of the basin’s seawaters. The prevailing hydrodynamic force for the circulation of coastal waters of Chalastra is wind stresses. The hydrodynamics of this coastal region may be further influenced by three rivers outflowing to the southwestern part of the basin; however, this runoff has dramatically decreased during the last few decades. Concerning the wind forcing regime, this is distinguished by two characteristic regimes. The first one is realized in winter and the other mainly in summer. Systematic field studies were conducted during one year for current and density measurements. Seawater samples were collected and chemically analyzed for dissolved oxygen, chlorophyll α and nutrients. Data revealed some cases of flow currents of opposite direction between the upper and the lower water layer, and a characteristic captured downwelling which seemed to evolve periodically on a diurnal time scale, especially in summer. Furthermore, a two layer mathematical model was developed and applied for the study of the water circulation and the investigation of downwelling processes under specific conditions; the tracing as well as the temporal and spatial evolution of these hydrodynamic processes in the mussels’ culture study area constituted the main aim of the present work. The formation of such events, which were observed mainly during summer periods, may affect the mussels’ development and has to be considered when designing farming practices in the area.

The Spatial Pattern of Midsummer Drought as a Possible Mechanistic Response to Lower-Tropospheric Easterlies over the Intra-Americas Seas

Abstract Following the idea that large-scale wind perturbations cause repeatable rainfall patterns over small tropical islands, the spatial pattern of the midsummer drought (MSD) is investigated as a repeatable rainfall pattern over the Intra-Americas Seas (IAS). For that, statistical techniques, including linear regressions, canonical correlation analysis, and variance budgets, were applied to the Tropical Rainfall Measuring Mission and ERA-Interim datasets to assess 1) the MSD pattern repeatability and 2) its explained variance in different time scales. As shown by the results, the MSD pattern is not a unique feature of the boreal summer intraseasonal variability in the IAS: it is more robust during summer but it exists in all rainy seasons on daily, intraseasonal, and interannual time scales. On diurnal time scales, the MSD pattern explains a negligible part of the total variance during summer (&amp;lt;2%), but on interannual scales it explains up to 20% and it captures the spatial features of “El Niño” rainfall anomalies. On all time scales, the MSD pattern is accompanied by repeatable wind and pressure patterns: anomalous lower-tropospheric (925 hPa) easterlies over a domain-wide meridional northward pressure gradient. These results provide evidence for the hypothesis that the MSD pattern manifests an underlying geographically determined, mechanistic pattern. Also, they suggest that the repeatable MSD-shaped rainfall and wind patterns could be extrapolated in time to better understand the climatic conditions behind droughts and pluvials, and to diagnose the causes behind rainfall trends.

An Idealized Description for the Diurnal Cycle of the Dry Atmospheric Boundary Layer

Abstract We present a conceptual model for the diurnal cycle of the dry atmospheric boundary layer (ABL). It may serve as a framework for future numerical studies on the transitional dynamics that characterize the ABL over land. The conceptual model enables us to define expressions for relevant physical scales as a function of the most prominent forcing parameters and the low degree of complexity facilitates a dimensionless description. This is useful to help generalize boundary layer dynamics that occur on a diurnal time scale. Further, the model’s application for numerical studies is illustrated herein with two examples: a single-column-model study that assesses the effect of wind forcing on the main characteristics of the diurnal cycle, and a large-eddy-simulation study on the daily evolution of turbulence under weak-wind-forcing conditions. The results from these studies sketch the general evolution of the present set of diurnal-cycle systems in more detail. We discuss how the setups are able to reproduce well-known dynamical features of the ABL and also highlight limitations, where the simple conceptual system is unable to describe realistic ABL behavior. We conclude that the present conceptual model has an interesting balance between model-system complexity and physical realism, such that it is useful for future idealized studies on the diurnal cycle of the ABL.