Changes in the characteristics of austral winter (June–July–August) synoptic activity in three domains (Africa, Australia and South America) of the extratropical Southern Hemisphere projected with ...the Regional Climate Model version 4 (RegCM4) are presented. The model is nested in three global climate models (GCMs) from the Coupled Model Intercomparison Project phase 5 (CMIP5) under the Representative Concentration Pathway 8.5. The model grid spacing is 25 km and the simulations cover the period 1970–2100. Synoptic activity is analyzed using both Eulerian and Lagrangian approaches. The Eulerian analysis shows an increase of the synoptic activity south of 40° S in the RegCM4 and GCMs ensembles for the future (2080–2099) compared to the present (1995–2014), but this signal does not necessarily indicate an increase in the cyclone frequency since it includes cyclonic and anticyclonic features. The Lagrangian analysis, however, indicates a decrease in the frequency of cyclones, with a positive tendency towards stronger systems, although the latter is not statistically significant at 95% confidence level. Lifetime, traveled distance and mean speed of the cyclones do not present statistically significant changes in the future climate. On the other hand, a significant increase in both intensity and extension of areas affected by precipitation associated with cyclones is found. As a consequence, there is a statistically significant trend of individual cyclones to produce more rainfall in the future.
The passage of three cold fronts (CFs) over the Gulf of Mexico was simulated with the Weather Research and Forecasting model to study the mechanisms associated with the formation of a jet parallel to ...the Sierra Madre Oriental (SMOr) mountain range near the port of Veracruz. Dew‐point temperature (Td = 20 °C) and available convective potential energy best simulated the horizontal propagation of the intense CFs over the Gulf, and equivalent potential temperature helped identify the vertical position of the fronts. Additional simulations with reduced topography showed that mountain heights exceeding 2.5 km, where the SMOr is closest to the coast, were crucial for the formation of a coastal barrier jet. The Froude number (Fr < 1) and the ageostrophic component of the wind at low levels were used to identify the formation of the jet; the Rossby radius of deformation determined its horizontal extent which was 81 km into the Gulf of Mexico in agreement with scatterometer winds during one of the CFs. The interaction of the northeasterly winds (known as Nortes) with the topography produced a blocking effect resulting in a stable region of cold air, a rain‐shadow and a coastal barrier jet of northwesterly direction, which generated strong cold air advection and subsidence in comparison with adjacent zones. The jet region appears as a minimum in the winter precipitation climatology indicating that the barrier jet is an important intraseasonal feature. In two of the case‐studies, maximum jet velocities reached those of a tropical storm (>18 m s−1) and occurred near the surface (<1 km above mean sea level), consistent with observations and similar to other barrier jets in the world. For the first time the jet near the port of Veracruz is documented as a coastal barrier jet. The CFs also produced strong Tehuano gap winds.
Simulations and observations of three cold fronts showed the formation of a coastal barrier jet near the port of Veracruz, Mexico due to their interaction with the Sierra Madre Oriental. In the jet region, strong northerly winds favoured cold air advection that stabilized the atmosphere and inhibited ascending motion generating a minimum of precipitation. The jets only formed with terrain heights exceeding 2.5 km near the coast. For the first time a coastal barrier jet is documented for this region.
Abstract California experienced a historic run of nine consecutive landfalling atmospheric rivers (ARs) in three weeks’ time during winter 2022/23. Following three years of drought from 2020 to 2022, ...intense landfalling ARs across California in December 2022–January 2023 were responsible for bringing reservoirs back to historical averages and producing damaging floods and debris flows. In recent years, the Center for Western Weather and Water Extremes and collaborating institutions have developed and routinely provided to end users peer-reviewed experimental seasonal (1–6 month lead time) and subseasonal (2–6 week lead time) prediction tools for western U.S. ARs, circulation regimes, and precipitation. Here, we evaluate the performance of experimental seasonal precipitation forecasts for winter 2022/23, along with experimental subseasonal AR activity and circulation forecasts during the December 2022 regime shift from dry conditions to persistent troughing and record AR-driven wetness over the western United States. Experimental seasonal precipitation forecasts were too dry across Southern California (likely due to their overreliance on La Niña), and the observed above-normal precipitation across Northern and Central California was underpredicted. However, experimental subseasonal forecasts skillfully captured the regime shift from dry to wet conditions in late December 2022 at 2–3 week lead time. During this time, an active MJO shift from phases 4 and 5 to 6 and 7 occurred, which historically tilts the odds toward increased AR activity over California. New experimental seasonal and subseasonal synthesis forecast products, designed to aggregate information across institutions and methods, are introduced in the context of this historic winter to provide situational awareness guidance to western U.S. water managers.
An intercomparison of three regional climate models (RCMs) (PRECIS‐HadRM3P, RCA4, and RegCM4) was performed over the Coordinated Regional Dynamical Experiment (CORDEX)—Central America, Caribbean, and ...Mexico (CAM) domain to determine their ability to reproduce observed temperature and precipitation trends during 1980–2010. Particular emphasis was given to the North American monsoon (NAM) and the mid‐summer drought (MSD) regions. The three RCMs show negative (positive) temperature (precipitation) biases over the mountains, where observations have more problems due to poor data coverage. Observations from the Climate Research Unit (CRU) and ERA‐Interim show a generalized warming over the domain. The most significant warming trend (≥0.34°C/decade) is observed in the NAM, which is moderately captured by the three RCMs, but with less intensity; each decade from 1970 to 2016 has become warmer than the previous ones, especially during the summer (mean and extremes); this warming appears partially related to the positive Atlantic Multidecadal Oscillation (+AMO). CRU, GPCP, and CHIRPS show significant decreases of precipitation (less than −15%/decade) in parts of the southwest United States and northwestern Mexico, including the NAM, and a positive trend (5–10%/decade) in June–September in eastern Mexico, the MSD region, and northern South America, but longer trends (1950–2017) are not statistically significant. RCMs are able to moderately simulate some of the recent trends, especially in winter. In spite of their mean biases, the RCMs are able to adequately simulate inter‐annual and seasonal variations. Wet (warm) periods in regions affected by the MSD are significantly correlated with the +AMO and La Niña events (+AMO and El Niño). Summer precipitation trends from GPCP show opposite signs to those of CRU and CHIRPS over the Mexican coasts of the southern Gulf of Mexico, the Yucatan Peninsula, and Cuba, possibly due to data limitations and differences in grid resolutions.
We assessed the performance of three regional models (PRECIS, RCA4, and RegCM4) in reproducing observed temperature and precipitation trends over the CORDEX‐CAM during 1980–2010. Most of the domain shows a warming trend, but the NAM region shows the most significant warming and drying trends, which are partially captured by the models. Each decade from 1970 to 2016 has become warmer than the previous ones, especially during the summer; this trend is partially linked to the Atlantic multidecadal oscillation. In the figure, trends of (a) mean annual temperature (°C/decade) and (b) annual precipitation (mm/decade) from CRU observations for the 1980–2010 period.
The interannual variability of the boreal winter (DJF) subtropical jet stream (STJ) is analyzed over the Coordinated Regional Downscaling Experiment—Central America, Mexico, and Caribbean domain ...(CORDEX-CAM) during 1980–2010. We use simulations with the regional climate model RegCM4 (version 7) at 25 km resolution driven by ERA-Interim (RegERA) and three global models (RegGCMs). The simulations are evaluated using zonal winds at 200 hPa level from ERA-Interim and MERRA2, which show similar results, and no significant trends in the STJ. Despite some biases, RegERA captures the STJ variability and its relationship with several teleconnections. The polarities of the principal mode of variability of the Pacific and Atlantic jets are significantly anti-correlated; they represent the longitudinal extension/retraction and the poleward/equatorward migration of the jet cores, respectively. During El Niño and the + PNA (Pacific North America), the North Pacific jet exit region and the North Atlantic jet show maximum speeds equatorward of their climatological positions. During these conditions, there is an extended and strong STJ over the domain; this pattern also tends to occur during the negative phases of the Arctic and North Atlantic oscillations. The RegGCMs simulate better the principal modes of the Atlantic jet variability than those of the Pacific jet exit region; nevertheless, they reproduce the observed sign of the variations of the jet speeds and their latitudinal changes in the two basins. They also partially capture the sign of the temperature and precipitation anomalies in the domain, which respond to the STJ polarities and their interaction with the teleconnections.
Abstract We describe the first effort within the Coordinated Regional Climate Downscaling Experiment–Coordinated Output for Regional Evaluation, or CORDEX-CORE EXP-I. It consists of a set of ...twenty-first-century projections with two regional climate models (RCMs) downscaling three global climate model (GCM) simulations from the CMIP5 program, for two greenhouse gas concentration pathways (RCP8.5 and RCP2.6), over nine CORDEX domains at ∼25-km grid spacing. Illustrative examples from the initial analysis of this ensemble are presented, covering a wide range of topics, such as added value of RCM nesting, extreme indices, tropical and extratropical storms, monsoons, ENSO, severe storm environments, emergence of change signals, and energy production. They show that the CORDEX-CORE EXP-I ensemble can provide downscaled information of unprecedented comprehensiveness to increase understanding of processes relevant for regional climate change and impacts, and to assess the added value of RCMs. The CORDEX-CORE EXP-I dataset, which will be incrementally augmented with new simulations, is intended to be a public resource available to the scientific and end-user communities for application to process studies, impacts on different socioeconomic sectors, and climate service activities. The future of the CORDEX-CORE initiative is also discussed.
The passage of three cold fronts ( CFs ) over the Gulf of Mexico was simulated with the Weather Research and Forecasting model to study the mechanisms associated with the formation of a jet parallel ...to the Sierra Madre Oriental ( SMOr ) mountain range near the port of Veracruz. Dew‐point temperature ( T d = 20 °C) and available convective potential energy best simulated the horizontal propagation of the intense CFs over the Gulf, and equivalent potential temperature helped identify the vertical position of the fronts. Additional simulations with reduced topography showed that mountain heights exceeding 2.5 km, where the SMOr is closest to the coast, were crucial for the formation of a coastal barrier jet. The Froude number (Fr < 1) and the ageostrophic component of the wind at low levels were used to identify the formation of the jet; the Rossby radius of deformation determined its horizontal extent which was 81 km into the Gulf of Mexico in agreement with scatterometer winds during one of the CFs . The interaction of the northeasterly winds (known as Nortes) with the topography produced a blocking effect resulting in a stable region of cold air, a rain‐shadow and a coastal barrier jet of northwesterly direction, which generated strong cold air advection and subsidence in comparison with adjacent zones. The jet region appears as a minimum in the winter precipitation climatology indicating that the barrier jet is an important intraseasonal feature. In two of the case‐studies, maximum jet velocities reached those of a tropical storm (>18 m s −1 ) and occurred near the surface (<1 km above mean sea level), consistent with observations and similar to other barrier jets in the world. For the first time the jet near the port of Veracruz is documented as a coastal barrier jet. The CFs also produced strong Tehuano gap winds.
La sequía de la península de Yucatán Estrada-Medina, Héctor; Cobos-Gasca, Víctor; Acosta-Rodríguez, José Luis ...
Tecnología y ciencias del agua,
09/2016, Letnik:
7, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Resumen: La sequía es uno de los fenómenos naturales más difíciles de estudiar debido a que no se cuenta con una definición lo suficientemente clara ni con los recursos técnicos para poder ...predecirla. Es un problema que, en el mundo, se ha incrementado en las últimas décadas como consecuencia del cambio climático. En México, la sequía afecta a más personas que cualquier otra contingencia natural, por lo que se requiere estudiarla para poder prevenir y mitigar sus efectos. En la península de Yucatán (PY), zona privilegiada por tener un vasto manto acuífero, la sequía no se presenta de manera tan catastrófica como en otros estados de la república. La sequía produce pérdidas y bajo rendimiento de cultivos, cabezas de ganado y colmenas, disminución de la calidad de los productos, así como incremento en los costos de producción, lo que produce reducción en el ingreso de los productores. A nivel de los organismos operadores no se registra baja en la disponibilidad de agua durante la época de sequía y sólo se reporta su disminución para consumo humano en algunas localidades en donde el acuífero se encuentra muy profundo o la calidad natural del agua no es adecuada para consumo humano. Sin embargo, al depender la PY casi en su totalidad del acuífero para el abasto del agua, su disponibilidad podría disminuir súbitamente por problemas en la infraestructura del sistema operador o de contaminación (importante por la permeabilidad del sustrato geológico y porque no existen sistemas de drenaje y potabilización de agua suficientes).
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