Lake and Land Breezes at a Mediterranean Artificial Lake: Observations in Alqueva Reservoir, Portugal

The Alqueva reservoir, in the Southeast of Portugal, has significantly changed the landscape of the region, with impacts also on the local climate, as documented in this manuscript, namely the thermal circulation in the form of lake and land breezes. Taking advantage of three strategic meteorological stations, two installed at the shores and another on a floating platform located near the center of the reservoir, a detailed analysis of lake and land breeze occurrences during two years is presented in this study. The thermal gradient between the reservoir and the surroundings is the main driver for the breeze development and the meteorological stations placed in opposite sides of the reservoir allow to establish the criteria in order to detect lake and land breezes. The results showed more land breeze than lake breeze occurrences, in line with the more negative thermal gradient between shores and reservoir in the annual cycle. Lake breezes are more frequent in summer months during daytime and land breezes in turn are more frequent in winter months during night-time.

Interaction of the Vertical Profile of Dust Aerosols with Land/sea Breezes over the Eastern Coast of the Red Sea from LIDAR and High-resolution WRF-Chem Simulations

<p>With the advances in modeling approaches, and the application of satellite and ground-based data in dust-related research, our understanding of the dust cycle is significantly improved in recent decades. However, two aspects of the dust cycle, the vertical profiles and diurnal cycles of dust aerosols have not been understood adequately, mainly due to the sparsity of observations. A micro-pulse LIDAR has been operating at the King Abdullah University of Science and Technology (KAUST) campus located on the east coast of the Red Sea (22.3N, 39.1E), measuring the backscattering from atmospheric aerosols at a high temporal resolution for several years since 2015. It is the only operating LIDAR system over the Arabian Peninsula. We use this LIDAR data together with other collocated observations and high-resolution WRF-Chem model simulations to study the 3-d structure of aerosols, with a focus on dust over the Red Sea Arabian coastal plains. </p><p>Firstly, we investigate the vertical profiles of aerosol extinction and concentration in terms of their seasonal and diurnal variability. Secondly, using the hourly model output and observations, we study the diurnal cycle of aerosols over the site. Thirdly, we explore the interactions between dust aerosols and land/sea breezes, which are the critical components of the local diurnal circulation in the region. </p><p>We found a substantial variation in the vertical profile of aerosols in different seasons. There is also a marked difference in the daytime and nighttime vertical distribution of aerosols in the study site, as shown by LIDAR data. A prominent dust layer is observed at ~5-7km at night in the LIDAR data, corresponding to the long-range transported dust of non-local origin. The vertical profiles of aerosol extinction are consistently reproduced in LIDAR, MERRA-2 reanalysis, and CALIOP data, as well as in WRF-Chem simulations in all seasons. Our results show that the sea breezes are much deeper (~1km) than the land breezes (~200m), and both of them prominently affect the distribution of dust aerosols over the study site. Sea breezes mainly trap the dust aerosols near the coast, brought by the northeasterly trade winds from inland deserts, causing elevated dust maxima at the height of ~1.5km. Also, sea and land breezes intensify dust emissions from the coastal region in daytime and nighttime, respectively. Such dust emissions caused by sea breezes and land breezes are most active in spring and winter. Finally, WRF-Chem successfully captures the onset, demise, and the height of some large-scale dust events as compared to LIDAR data qualitatively. </p>

Diurnal Variation of Rainfall in a Tropical Coastal Region with Complex Orography

We examined the diurnal cycle of the rainfall in a coastal tropical mountainous region in central Veracruz State, Mexico (18°–21° N, 95.5°–98.5° W), featuring a striking topographic gradient running from sea level at the Gulf of Mexico coast to 5000 m above sea level (m.a.s.l.) in less than 100 km horizontal distance. During the summer, this unique location leads to regular the interaction between the easterly moisture inflow and the mountainous barrier. Over the complex terrain, forced ascent leads the occurrence of maximum rainfall during the afternoon (16–19 local time, LT ≈ 1½ hours ahead of solar time in summer), first along the slope and later over the coast. Along the coastal plain, the precipitation continues until the early morning consistent with there being convergence between land breezes and the trade winds. Observations obtained during a measurement campaign from 28 June to 3 July 2015, indicate that during the early evening downslope winds move against easterly flow, likely due to katabatic outflows previously observed over the region. These features are confirmed using spatial (0.88°) and temporal (30 min) resolution CMORPH rainfall estimates, since we observed evening episodes initiating along the slope during the afternoon (14–17 LT) moving later towards the coast.

On the Climatological Use of Radar Data Mosaics: Possibilities and Challenges

Continental mosaics of radar data have now been generated for more than 20 years. They offer information on precipitation climatology that is simply not available or archived elsewhere: How often does it rain at any particular location? At what time? And with what intensity distribution? What are the geographical and temporal patterns of precipitation occurrence, formation, and decay? What is the climatology of severe weather? Answers to these questions have value on their own and invariably trigger more questions about the processes causing these patterns but also suggest some answers. They also have considerable pedagogical value in illustrating in the classroom the impacts of different processes—such as sea–land breezes, topography, and seasons—on precipitation. In this work, U.S. mosaics of radar data from 1996 to 2015 are used to demonstrate the possibilities offered by such a dataset. Three topics are discussed: (i) climatologies and daily cycles of precipitation and convection, and what they can teach us about precipitation mechanisms; (ii) the spatial and temporal distribution of the appearance and occurrence of convection, and what it reveals about the importance of surface terrain properties for these events; and (iii) the power and challenges of looking for a small signal in such a large dataset using the influence of weekly activity cycles and cities on precipitation as an illustration.