Changes in northern hemisphere temperature variability shaped by regional warming patterns

Global warming involves changes not only in the mean atmospheric temperature, but also in its variability and extremes. Here we use a feature-tracking technique to investigate the dynamical contribution to temperature anomalies in the northern hemisphere in CMIP5 climate-change simulations. We develop a simple theory to explain how temperature variance and skewness changes are generated dynamically from mean temperature gradient changes, and demonstrate the crucial role of regional warming patterns in shaping the distinct response of cold and warm anomalies. We also show that skewness changes must be taken into account, in addition to variance changes, in order to correctly capture the projected temperature variability response. These changes in variability may impact humans, agriculture and animals, as they experience not only a warmer mean climate, but also a new likelihood of temperature anomalies within that climate

Dynamical downscaling of historical climate over CORDEX Central America domain with a regionally coupled atmosphere–ocean model

The climate in Mexico and Central America is influenced by the Pacific and the Atlantic oceanic basins and atmospheric conditions over continental North and South America. These factors and important ocean–atmosphere coupled processes make the region’s climate a great challenge for global and regional climate modeling. We explore the benefits that coupled regional climate models may introduce in the representation of the regional climate with a set of coupled and uncoupled simulations forced by reanalysis and global model data. Uncoupled simulations tend to stay close to the large-scale patterns of the driving fields, particularly over the ocean, while over land they are modified by the regional atmospheric model physics and the improved orography representation. The regional coupled model adds to the reanalysis forcing the air–sea interaction, which is also better resolved than in the global model. Simulated fields are modified over the ocean, improving the representation of the key regional structures such as the Intertropical Convergence Zone and the Caribbean Low Level Jet. Higher resolution leads to improvements over land and in regions of intense air–sea interaction, e.g., off the coast of California. The coupled downscaling improves the representation of the Mid Summer Drought and the meridional rainfall distribution in southernmost Central America. Over the regions of humid climate, the coupling corrects the wet bias of the uncoupled runs and alleviates the dry bias of the driving model, yielding a rainfall seasonal cycle similar to that in the reanalysis-driven experiments.Universidad de Costa Rca/[805-B7-507]/UCR/Costa RicaCRYOPERU/[144-2015]//PerúUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigaciones Geofísicas (CIGEFI

Characteristic atmospheric states during mid‑summer droughts over Central America and Mexico

Open AccessAnnual precipitation over Central America and large areas of Mexico is typically characterised by its bimodal distribution, with a precipitation minimum in July to August that occurs between two separate maxima from May to July and August to October. Several theories have been proposed to explain this phenomenon, which is often termed the mid-summer drought (MSD), but most fail to address the diferent characteristics associated with individual MSD events. Here, a regression-based approach is used to detect and quantify the annual and climatological MSD signature over Central America and Mexico. This approach has been evaluated and shown to be robust for various datasets with diferent spatial resolutions. It was found that in the southeast of the Mexico/Central America region, MSDs start earlier and end later than elsewhere, and are thus longer in duration. However, the coast of the Gulf of Mexico, Cuba, and large areas of Central America, exhibit climatologically stronger MSDs. Changes in precipitation, brought about by the interaction between reversals of the onshore/ofshore winds and orographic forcing associated with the steep mountainous terrain, have also been shown to be signifcant factors in the timing of MSD occurrences, ofering support for a combined theory of large-scale dynamics and regional forcing. Using self-organising maps (SOMs) as an analysis tool, it was found that MSD events over the domain display strong spatial variability. The MSDs over the domain also generate distinct signatures and may be forced by particular mechanisms. We found that El Niño-Southern Oscillation (ENSO) could be a potential classifer for the SOM identifed atmospheric states, based on the correspondence of MSD occurrences with ENSO phasesLa precipitación anual sobre Centroamérica y grandes áreas de México se caracteriza típicamente por su distribución bimodal, con un mínimo de precipitación en julio a agosto que ocurre entre dos máximos separados de mayo a julio y de agosto a octubre. Se han propuesto varias teorías para explicar este fenómeno, que a menudo se denomina sequía de mediados de verano (TME), pero la mayoría no aborda las diferentes características asociadas con los eventos de TME individuales. Aquí, se utiliza un enfoque basado en regresión para detectar y cuantificar la firma anual y climatológica de MSD en Centroamérica y México. Este enfoque ha sido evaluado y ha demostrado ser robusto para varios conjuntos de datos con diferentes resoluciones espaciales. Se encontró que en el sureste de la región de México / Centroamérica, los TME comienzan antes y terminan más tarde que en otros lugares y, por lo tanto, tienen una duración más prolongada. Sin embargo, la costa del Golfo de México, Cuba y grandes áreas de Centroamérica exhiben TME climatológicamente más fuertes. Los cambios en la precipitación, provocados por la interacción entre las reversiones de los vientos en tierra / de tierra y el forzamiento orográfico asociado con el terreno montañoso escarpado, también han demostrado ser factores significativos en el momento de la ocurrencia de TME, ofreciendo apoyo para una teoría combinada de grandes dimensiones. -Dinámica de escala y forzamiento regional. Utilizando mapas autoorganizados (SOM) como herramienta de análisis, se encontró que los eventos de MSD en el dominio muestran una fuerte variabilidad espacial. Los MSD sobre el dominio también generan firmas distintas y pueden ser forzados por mecanismos particulares. Descubrimos que El Niño-Oscilación del Sur (ENOS) podría ser un clasificador potencial para los estados atmosféricos identifcados por la MOS, con base en la correspondencia de las ocurrencias de MSD con las fases del ENOS.Universidad de Melbourne, AustraliaUniversidad de Tasmania, AustraliaUniversidad de Dalhousie, CanadáUniversidad Nacional, Costa RicaDepartamento de Físic