<p><span>Atmospheric water vapor plays a key role in weather and climate. Knowledge about its variability, diurnal and seasonal cycles, as well as its long-term trend is necessary to improve our understanding of the hydrological cycle. H2O total columns are measured by the two remote sensing techniques, ground-based solar absorption FTIR spectroscopy and a GPS (Global Positioning System) receiver, over a site in central Mexico. The Altzomoni Atmospheric Observatory (3989 m a.s.l., 19.32ºN, 98.65ºW) is a high altitude station located within the Izta-Popo national park, 60 km SE from Mexico City. The time series of GPS and FTIR show a high correlation between coincident hourly means. Both techniques are complementary since despite that GPS works throughout day and night and also in cloudy and rainy weather conditions, the FTIR data provides in addition altitude-resolved information about the atmospheric water vapor and permits to distinguish different isotopes.</span></p><p><span>In this study, we show water vapor columns in the 2013 to 2019 period for this region retrieved from FTIR and GPS measurements and preliminary results about their isotopic composition (H216O, H218O and HD16O). We discuss the opportunity to study the hydrological cycle in central Mexico using the relationship between light and heavy isotopes, a relationship that gives valuable information about the sources and transport pathways.</span></p>

This study examined the evolution of the beach profile and sedimentary balance in Playa del Coco, Mexico, during one year (September 2013–September 2014) to monitor these conditions at a site with little or no anthropogenic influence. The type of beach profile was determined according to the energy profile of the geomorphology, resulting in three types of profiles: low, medium, and high energy. In addition, sediment volumes were quantified, and erosion or accumulation at each study site was described. The results showed that the medium-energy profile was characteristic of the beach most of the time. High-energy conditions were recorded only once due to the influence of a high-category hurricane (Odile, III) during the hurricane season. The dominant sediment size was medium, moderately well-classified to well-classified, coinciding with the medium-energy profile. Coarse, well-sorted sand was recorded at the end of the study, coinciding with the highest loss of sediment on the beach. Playa del Coco showed a state of quasi-equilibrium before the end of the annual cycle, recovering the characteristics of the beach at the beginning of the study. After that time, there was a great loss of sedimentary material influenced by Hurricane Odile (III), modifying the beach’s state of recovery. Therefore, the stability of this beach could be cyclical and respond to the self-organization principle rather than to seasonal parameters. However, the duration of the cycles that influence Playa del Coco seems to be determined by the hurricane season, especially the combination of two main factors: the proximity to the coast of the hurricane and the amount of rainfall associated with the hurricane.

<p><span>Knowledge about water vapor isotopologues is a useful tool in the study of the hydrological cycle. Total columns of water vapor isotopologues (H</span><sub><span>2</span></sub><sup><span>16</span></sup><span>O, H</span><sub><span>2</span></sub><sup><span>18</span></sup><span>O and HD</span><sup><span>16</span></sup><span>O) are measured by ground-based solar absorption FTIR spectroscopy at Altzomoni (3985 m.a.s.l, 19.12ºN, 98.66ºW), a high altitude subtropical remote background site in central Mexico (Barthlott et al., 2017). In the contribution we present the time series of the isotopic composition of water vapor columns and profiles above central Mexico and analyze differences in the isotopic ratios of H</span><sub><span>2</span></sub><sup><span>16</span></sup><span>O, H</span><sub><span>2</span></sub><sup><span>18</span></sup><span>O and HD</span><sup><span>16</span></sup><span>O between the rain and dry seasons of the year: in the rain season, changes in the isotopic ratios might be dominated by the diurnal cycle, which correlates with the relative humidity, temperature and dew point, while isotopic ratio in the dry season might depend more on the origin of the air parcels and transportation. We discuss the hydrological cycle in central Mexico using the relationship between light and heavy isotopes, and how this relationship gives valuable information about the pathways, sources and transport.</span></p>

Total column H2O is measured by two remote sensing techniques at the Altzomoni Atmospheric Observatory (19° 12'N, 98° 65'W, 4000 m a.s.l.), a high-altitude, tropical background site in central Mexico. A ground-based solar absorption FTIR spectrometer that is part of the Network for Detection of Atmospheric Composition Change (NDACC) is used to retrieve water vapor in three spectral regions (6074-6471, 2925-2941 and 1110-1253 cm-1) and is compared to data obtained from a GPS (Global Positioning System) receiver that is part of the TLALOCNet GPS-meteorological network. Strong correlations are obtained between the coincident hourly means from the three FTIR products and small relative bias and correction factors could be determined for each when compared to the more consistent GPS data. Retrievals from the 2925-2941 cm-1 spectral region have the highest correlation with GPS (R2= 0.998, std= 0.18 cm (78.39%), mean diff= 0.04 cm (8.33%)), although the other products are also highly correlated (R2= >0.99, std= <0.20 cm (< 90%), mean diff= < 0.1 cm (< 24%)). Clear-sky, dry bias (CSDB) values are reduced to <10% (< 0.20 cm) when coincident hourly means are used in the comparison. The use of GPS and FTIR water vapor products simultaneously leads to a more complete and better description of the diurnal and seasonal cycles of water vapor. We describe the water vapor climatology with both complementary data sets, nevertheless, pointing out the importance of considering the clearsky dry bias arising from the large diurnal and seasonal variability of water vapor at this high-altitude tropical site.