Simulating and understanding the gap outflow and oceanic response over the Gulf of Tehuantepec during GOTEX

17 USC 105 interim-entered record; under review.Tehuantepecer is a strong mountain gap wind traveling through Chivela Pass into eastern Pacific coastin southern Mexico, most commonly between October and February and brings huge impacts on local and surrounding meteorology and oceanography. Gulf of Tehuantepec EXperiment (GOTEX) was conducted in February 2004 to enhance the understanding of the strong offshore gap wind, ocean cooling, vertical circulations and interactions among them. The gap wind event during GOTEX was simulated using the U.S. Navy Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS® ). The simulations are compared and validated with the observations retrieved from several satellites (GOES 10–12, MODIS/Aqua/Terra, TMI, and QuikSCAT) and Airborne EXpendable BathyThermograph (AXBT). The study shows that the gap wind outflow has a fanlike pattern expending from the coast and with a strong diurnal variability. The surface wind stress and cooling along the axis of the gap wind outflow caused intense upwelling and vertical mixing in the upper ocean; both contributed to the cooling of the ocean mixed layer under the gap wind. The cooling pattern of sea surface temperature (SST) also reflects temperature advection by the nearby ocean eddies to have a crescent shape. Two sensitivity experiments were conducted to understand the relative roles of the wind stress and heat flux on the ocean cooling. The control has more cooling right under the gap flow region than either the wind-stress-only or the heat-flux-only experiment. Overall, the wind stress has a slightly larger effect in bringing down the ocean temperature near the surface and plays a more important role in local ocean circulations beneath the mixed layer. The impact of surface heat flux on the ocean is more limited to the top 30 m within the mixed layer and is symmetric to the gap flow region by cooling the ocean under the gap flow region and reducing the warming on both sides. The effect of surface wind stress is to induce more cooling in the mixed layer under the gap wind through upwelling associated with Ekman divergence at the surface. Its effect deeper down is antisymmetric related to the nearby thermocline dome by inducing more upwelling to the east side of the gap flow region and more downwelling on the west side. Diagnostics from the mixed layer heat budget for the control and sensitivity experiments confirm that the surface heat flux has more influence on the broader area and the wind stress has more influence in a deeper region.This research is supported by Office of Naval Research (ONR) through the Department Research Initiative Predictability of Seasonal and Intraseasonal Oscillations (PE061153N). Computational resources were supported in part by a grant of HPC time from the Department of Defense Major Shared Resource Centers, Stennis Space Center, Mississippi

Dynamics of Bora wind over the Adriatic sea: atmospheric water balance and role of air-sea fluxes and orography

The Bora wind is a mesoscale phenomenon which typically affects the Adriatic Sea basin for several days each year, especially during winter. The Bora wind has been studied for its intense outbreak across the Dinaric Alps. The properties of the Bora wind are widely discussed in the literature and scientific papers usually focus on the eastern Adriatic coast where strong turbulence and severe gust intensity are more pronounced. However, the impact of the Bora wind can be significant also over Italy, not only in terms of wind speed instensity. Depending on the synoptic pressure pattern (cyclonic or anticyclonic Bora) and on the season, heavy snowfall, severe storms, storm surges and floods can occur along the Adriatic coast and on the windward flanks of the Apennines. In the present work five Bora cases that occurred in recent years have been selected and their evolution has been simulated with the BOLAM-MOLOCH model set, developed at ISAC-CNR in Bologna. Each case study has been addressed by a control run and by several sensitivity tests, performed with the purpose of better understanding the role played by air-sea latent and sensible heat fluxes. The tests show that the removal of the fluxes induces modifications in the wind approching the coast and a decrease of the total precipitation amount predicted over Italy. In order to assess the role of heat fluxes, further analysis has been carried out: column integrated water vapour fluxes have been computed along the Italian coastline and an atmospheric water balance has been evaluated inside a box volume over the Adriatic Sea. The balance computation shows that, although latent heat flux produces a significant impact on the precipitation field, its contribution to the balance is relatively minor. The most significant and lasting case study, that of February 2012, has been studied in more detail in order to explain the impressive drop in the total precipitation amount simulated in the sensitivity tests with removed heat fluxes with respect to the CNTRL run. In these experiments relative humidity and potential temperature distribution over different cross-sections have been examined. With respect to the CNTRL run a drier and more stable boundary layer, characterised by a more pronounced wind shear at the lower levels, has been observed to establish above the Adriatic Sea. Finally, in order to demonstrate that also the interaction of the Bora flow with the Apennines plays a crucial role, sensitivity tests varying the orography height have been considered. The results of such sensitivity tests indicate that the propagation of the Bora wind over the Adriatic Sea, and in turn its meteorological impact over Italy, is influenced by both the large air-sea heat fluxes and the interaction with the Apennines that decelerate the upstream flow

Spatial and temporal dynamics of the hydrology at Salinas Bay, Costa Rica, Eastern Tropical Pacific.

Introduction: Salinas Bay is located in the warm pool of the Eastern Tropical Pacific (ETP), characterized by warm, shallow surface waters, a strong and shallow thermocline, and an important biological diversity. The primary productivity of the region is influenced by the coastal upwelling, which occurs during the boreal winter as a result of the strengthening of trade winds. Objective: To study the spatial and temporal dynamics of physical and chemical parameters at seven hydrographic stations in Salinas Bay, Costa Rica, through the analysis of CTD data, and relate the warm and cold events to the regional atmospheric conditions present when measuring the data. Methods: Seven hydrographic stations, sampled at Salinas Bay between August 2008 and December 2014, were selected. The variables processed for analysis are temperature, density, salinity, oxygen, chl-a and turbidity. Once the data was processed, 42 Hovmöller kind diagrams were plotted. Results: All variables, except turbidity, presented a seasonal periodicity associated with the upwelling. In general, colder and denser waters, higher salinity and chl-a concentrations and lower dissolved oxygen values were observed during the dry season, when the upwelling was active. Whereas, during the rainy season water masses were warmer and less dense, salinity and chl-a concentrations decreased and dissolved oxygen values tended to increase. Conclusions: The spatial and temporal dynamics of the hydrology in Salinas Bay was influenced by the coastal upwelling events. The region also presented an interannual variability associated with ENSO. Seasonal and interannual variability can counteract their effects on the oceanographic parameters when they coincide temporally.Universidad de Costa Rica/[808-A5-037]/UCR/Costa RicaUniversidad de Costa Rica/[805-B8-766]/UCR/Costa RicaUniversidad de Costa Rica/[805-B9-454]/UCR/Costa RicaUniversidad de Costa Rica/[EC-497]/UCR/Costa RicaUniversidad de Costa Rica/[805-C0-610]/UCR/Costa RicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigaciones Geofísicas (CIGEFI)UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de FísicaUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de BiologíaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR

Opposite trends of sea‑breeze speeds and gusts in Eastern Spain, 1961–2019

Most studies on wind variability have deepened into the stilling vs. reversal phenomena at global to regional scales, while the long-term changes in local-scale winds such as sea-breezes (SB) represent a gap of knowledge in climate research. The state-of-the-art of the wind variability studies suggests a hypothetical reinforcement of SB at coastal stations. We first developed a robust automated method for the identification of SB days. Then, by using homogenized wind observations from 16 stations across Eastern Spain, we identified 9,349 episodes for analyzing the multidecadal variability and trends in SB speeds, gusts and occurrence for 1961–2019. The major finding is the opposite trends and decoupled variability of SB speeds and gusts: the SB speeds declined significantly in all seasons (except for winter), and the SB gusts strengthened at the annual scale and in autumn–winter, being most significant in autumn. Our results also show that the SB occurrence has increased across most of Eastern Spain, although presenting contrasting seasonal trends: positive in winter and negative in summer. We found that more frequent anticyclonic conditions, NAOI + and MOI + are positively linked to the increased winter occurrence; however, the causes behind the opposite trends in SB speeds and gusts remain unclear. The SB changes are complex to explain, involving both large-scale circulation and physical-local factors that challenge the understanding of the opposite trends. Further investigation is needed to assess whether these trends are a widespread phenomenon, while climate models could simulate the drivers behind these decoupled SB changes in a warmer climate.This research was funded by the following projects: IBER-STILLING (RTI2018-095749-A-I00, MCIU/AEI/FEDER,UE); and VENTS (GVA-AICO/2021/023). C.A.M was granted by Ramon y Cajal fellowship (RYC-2017–22830), and supported by a 2021 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation

Interannual variability of sea surface temperature in the eastern tropical Pacific Ocean and Central American rainfall

Sea surface temperature (SST) in the east Pacific warm pool (EPWP) plays a potentially important role in Central American rainfall, tropical cyclogenesis, ocean biology, large-scale tropical heating, and the El Niño-Southern Oscillation (ENSO). The first part of this dissertation is aimed at understanding what processes govern the interannual variability of SST in the EPWP. Interannual wind stress, shortwave radiation, and precipitation were used as forcing to an ocean general circulation model. Shortwave heating was identified as the primary driver of the interannual SST tendency in the EPWP. The high correlation between the EPWP and the equatorial Pacific Ocean is explained by the fact that equatorial SST anomalies modify the distribution of atmospheric vertical motions and therefore cloud cover and shortwave heating. In a parallel set of experiments, the low-frequency variability of the Tehuantepec gap winds was also shown to have a considerable effect on that of SST in the EPWP. Motivated by the results of the first part of this dissertation, the second part offers significant improvements to the mean state of the equatorial Pacific Ocean in a climatology ocean model experiment by including the Galápagos Islands in the model topography. In this context, the equatorial cold bias is reduced. Furthermore, when the ocean model is coupled to the atmosphere through zonal wind stress, the problem of an excessively regular and biennial ENSO is also reduced. The change in ENSO timescale is a result of the same dynamics operating on a different mean state. The third part of this dissertation is aimed at understanding the role of the interannual variability of SST in the EPWP in that of Central American rainfall. An anomalously warm EPWP can trigger a rapid enhancement of the east Pacific intertropical convergence zone (ITCZ) in rainy seasons following peak ENSO events, which leads to a rainfall anomaly over Central America. Moreover, the timing and amplitude of the SST-enhanced ITCZ depends on the persistence of the ENSO event. The longer the equatorial SST anomaly persists, the longer the EPWP is subject to anomalous shortwave heating and thus the greater the subsequent SST enhancement of the ITCZ

Analysis of the ocean dynamics in a wind-jet region using high-resolution models

Pla de Doctorat Industrial de la Generalitat de CatalunyaThe water currents and the wave field at the Catalan coast (in the Northwestern Mediterranean Sea) are investigated. However, the main research is focused at the northern margin of the Ebro Shelf, where there is a relatively high amount of data for study purposes and where episodes of strong northwesterly wind occur. In such cases, the wind is channeled through the Ebro Valley and intensifies upon reaching the sea, resulting in a wind jet. The research has been divided into four parts: (1) the study of the water circulation induced by a wind jet, by means of the Regional Ocean Modeling System (ROMS) numerical model; (2) the study of the waves dynamics induced by a wind jet, using the Simulating WAves Nearshore (SWAN) numerical model; (3) the study of the wave-current interactions during wind-jet events, coupling the numerical models used formerly; and (4) the implementation and validation of a waves and currents forecasting system at the Catalan coast, based on the knowledge gained during the research performed in the previous parts.S'investiguen els corrents marins i l'onatge a la costa catalana (al nord-oest del Mar Mediterrani). Tanmateix, la recerca principal es centra al marge nord de la plataforma de l'Ebre, on hi ha una quantitat relativament alta de dades útils per a la investigació i on tenen lloc episodis de fort vent del nord-oest. En aquests casos, el vent és canalitzat al llarg de la vall de l'Ebre i s'intensifica quan arriba al mar, resultant en un wind jet. La investigació s'ha dividit en quatre parts: (1) l'estudi de la circulació de l'aigua induïda per un wind jet, utilitzant el model numèric Regional Ocean Modeling System (ROMS); (2) l'estudi de l'onatge induït per un wind jet, mitjançant el model numèric Simulating WAves Nearshore (SWAN); (3) l'estudi de les interaccions onatge-corrents durant episodis de wind jet, acoblant els models numèrics utilitzats anteriorment; i (4) la implementació i validació d'un sistema de predicció d'onatge i corrents a la costa catalana, basat en el coneixement adquirit durant la recerca realitzada en les parts anteriors.Postprint (published version

The global monsoon system: research and forecast

The main objective of this workshop was to provide a forum for discussion between researchers and forecasters on the current status of monsoon forecasting and on priorities and opportunities for monsoon research. WMO hopes that through this series of quadrennial workshops, the following goals can be accomplished: (a) to update forecasters on the latest reseach findings and forecasting technology; (b) to update researchers on monsoon analysis and forecasting; (c) to identify basic and applied research priorities and opportunities; (d) to identify opportunities and priorities for acquiring observations; (e) to discuss the approach of a web-based training document in order to update forecasters on developments of direct relevance to monsoon forecasting