CAPSULE SUMMARY A regional-scale observational experiment designed to address how the atmospheric boundary layer responds to spatial heterogeneity in surface energy fluxes.

Significant episodes of sudden nocturnal warming have been observed by the Mississippi Mesonet. The probable relation of these nocturnal warming events to surface layer regime transitions between a decoupled quiescent surface layer and a more turbulent, less thermodynamically stable surface layer is discussed within the context of four examples with different temporal signatures. In general, the changes in wind speed and inversion strength are consistent with expectations for such regime changes. However, details of individual events indicate a wider variety of event characteristics than has been documented previously. The cases examined are proposed as prototypes for four different types of warming event, based on the evolution of temperature and dewpoint as well as on whether clear forcing from a mesoscale or synoptic frontal passage can be identified. Using this classification system and a subjective evaluation of event magnitude, the frequency of nocturnal warming events is analyzed for four mesonet stations at varying distance inland over the period of record.

Mid‐Missouri experienced up to 2 min 40 s of totality at around solar noon during the total eclipse of 2017. We conducted the Mid‐Missouri Eclipse Meteorology Experiment to examine land‐atmosphere interactions during the eclipse. Here, research examining the eclipse responses in three contrasting ecosystems (forest, prairie, and soybeans) is described. There was variable cloudiness around first and fourth contacts (i.e., the start and end of partial solar obscuration) at the forest and prairie; however, solar irradiance (K↓) signals during the eclipse were relatively clean. Unfortunately, the eclipse forcing at the soybean field was contaminated by convective activity, which decreased K↓ beginning about an hour before first contact and exposed the field to cold outflow ~30 min before second contact. Turbulence was suppressed during the eclipse at all sites; however, there was also an amplified signal at the soybean field during the passage of a gust front. The standard deviations of the horizontal and vertical wind velocities and friction velocities decreased by ~75% at the forest (aerodynamically rough), and ~60% at the prairie (aerodynamically smooth). The eddy fluxes of energy were highly coherent with the solar forcing with the latent and sensible heat fluxes approaching 0 W/m2 and changing in direction, respectively. For the prairie site, we estimated a canopy‐scale time constant for the surface conductance light response of 10 min. Although the eclipse imparted large forcings on surface energy balances, the air temperature response was relatively muted (1.5–2.5 °C decrease) due to the absence of topographic effects and the relatively moist land and atmosphere.

High spatial/temporal resolution mobile transects were used to examine the thermal and moisture structure of the sea-breeze front (SBF) along the Mississippi coast during August 2014 and 2015. Compared to most similar studies, conditions were much warmer and more humid. Results show a 1-2 g/kg increase in mixing ratio across the mature SBF zone, and up to a 2.5°C temperature decrease. When SBF radar fine lines are identifiable, their position agrees very well with surface thermodynamic changes. Although temperatures were cooler at the coast, microscale offsets in location of thermal, moisture, and radiative features are noted in the vicinity of the SBF, particularly when the sea-breeze system is relatively weak or immature. At times, it seems that strong solar insolation causes the temperature to rise temporarily within the transition zone behind the kinematic SBF. These results are at variance with most other diagnostic studies. Some thermodynamic variations are noted within the marine air mass in connection to minor water bodies such as Biloxi Bay. The potential for passage of the SBF to at least temporarily increase human heat stress as described by heat index is also noted.

Atmospheric dispersion calculations are made using the HYSPLIT Particle Dispersion Model for studying the transport and dispersion of air-borne releases from point elevated sources in the Mississippi Gulf coastal region. Simulations are performed separately with three meteorological data sets having different spatial and temporal resolution for a typical summer period in 1-3 June 2006 representing a weak synoptic condition. The first two data are the NCEP global and regional analyses (FNL, EDAS) while the third is a meso-scale simulation generated using the Weather Research and Forecasting model with nested domains at a fine resolution of 4 km. The meso-scale model results show significant temporal and spatial variations in the meteorological fields as a result of the combined influences of the land-sea breeze circulation, the large scale flow OPEN ACCESS Int. J. Environ. Res. Public Health 2009, 61056 field and diurnal alteration in the mixing depth across the coast. The model predicted SO 2 concentrations showed that the trajectory and the concentration distribution varied in the three cases of input data. While calculations with FNL data show an overall higher correlation, there is a significant positive bias during daytime and negative bias during night time. Calculations with EDAS fields are significantly below the observations during both daytime and night time though plume behavior follows the coastal circulation. The diurnal plume behavior and its distribution are better simulated using the mesoscale WRF meteorological fields in the coastal environment suggesting its suitability for pollution dispersion impact assessment in the local scale. Results of different cases of simulation, comparison with observations, correlation and bias in each case are presented.