Cold Air Drainage Flows and their Relation to the Formation of Nocturnal Convective Clouds at the Eastern Andes of South Ecuador

The development of clouds has many causes, not all of those are examined. In consideration of rainfall behaviour and distribution knowledge of cloud formation, processes in the tropics are of particular importance. Clouds are part of the hydrological cycle, influencing water resources and the energy budget. The insight into unknown cloud generation processes is a great benefit in the developmental procedure of understanding the structure and functionality of an ecosystem and its biodiversity. The main objective of the presented study was to investigate an unidentified nocturnal cloud formation procedure in the eastern Andes of South Ecuador and the adjacent northern Peruvian Amazon. The central theses encompass the confluence of katabatic flows in highly complex terrain due to a concave configuration. This cold drainage of air induces a surface cold front in the foothills of the eastern Andes, which initiates moisture convection due to compressional lifting by the terrain; a nocturnal LLJ triggers the development of the MCS. For the evaluation of the hypotheses the numerical model ARPS was used to analyse the not fully understood highland - lowland interactions in the PBL. At first, simulations of an accurate katabatic flow and its behaviour in complex terrain were performed with optimal conditions and without location information. The main subject of the study was the confluence of the cold drainage of air as a result of concave-lined terrain. Simplified DEMs, inspired by the Andes, were used for this analysis, due to the very steep slopes and valleys of the real terrain. A stepwise increase in their complexity, beginning with a simple slope, enabled the examination of the impact of the terrain configuration on the flow’s dynamic behaviour. With the most complex terrain model, which represents a concave ridgeline interrupted by several valleys draining into a basin, the confluence of the downslope flows due to the geometry of the terrain was demonstrated. Thus, a representative, persistent, thermally driven flow was generated, creating a convergence line that was largest in the centre of the basin. Afterwards, a simulation of a katabatically induced surface cold front with subsequent convective cloud formation was performed with the same model framework, except for the atmospheric water vapour. The simulation showed the same confluence of the downslope flows with a convergence line inside the basin as before. The development of a katabatically induced cold front was identified based on characteristic attributes described in chapter 2 using a cross-section through this line. Furthermore, the results also showed a convergence line that was largest in the centre of the basin. Because of the initiation of moisture convection in this area, due to sufficient moisture in the atmosphere, it was evident that the terrain geometry was the triggering mechanism for cloud formation. The presence of an LLJ in the basin showed the intensification of the cloud formation process. However, the previous results showed that the cluster developed primarily due to compressional lifting by the terrain. This shows that the LLJ had marginal effects on the initiation of moisture convection, acting primarily as an enhancement of its occurrence. Finally, the spatial reference was enabled and the parametrisation set-up of the idealised studies was assigned and adjusted to a multi-nested, approximately realistic model setting, strengthening the evidence from the previous results. For the study, a specific situation, selected on the basis of GOES-E satellite data was used. The main subject was the demonstration of the development of an MCS in the foothills of the eastern Andes due to the presence of katabatic flows as the driving mechanism. The GOES-E brightness temperatures were used to compare the satellite-observed data with the ARPS data to verify the simulated cloud appearance. Due to the fact that the 4 km domain revealed no convective clouds, but a convective cloud cluster was generated on the 1 km domain, a scale dependency was determined. This was caused by two factors: first of all, the NBL processes were simulated more accurately due to the higher vertical resolution, thus more accurately representing the katabatic flows. Furthermore, the higher resolved domain represented a more structured terrain, resulting in stronger convergences of the downslope flows. The comparison of the satellite and the modelled data presented a good agreement concerning the orientation, the location as well as the cold tops of the cells. A closer look at the NBL revealed cold air drainage, nourishing the cell regeneration. The typical characteristics, discussed in the idealised study without location information, confirmed the occurrence of thermally induced downslope flows as the driving process behind convective initiation

Rainfall and Cloud Dynamics in the Andes: A Southern Ecuador Case Study

Mountain regions worldwide present a pronounced spatiotemporal precipitation variability, which added to scarce monitoring networks limits our understanding of the generation processes involved. To improve our understanding of clouds and precipitation dynamics and cross-scale generation processes in mountain regions, we analyzed spatiotemporal rainfall patterns using satellite cloud products (SCP) in the Paute basin (900–4200 m a.s.l. and 6481 km2) in the Andes of Ecuador. Precipitation models, using SCP and GIS data, reveal the spatial extension of three regimes: a three-modal (TM) regime present across the basin, a bimodal (BM) regime, along sheltered valleys, and a unimodal (UM) regime at windward slopes of the eastern cordillera. Subsequently, the spatiotemporal analysis using synoptic information shows that the dry season of the BM regime during boreal summer is caused by strong subsidence inhibiting convective clouds formation. Meanwhile, in UM regions, low advective shallow cap clouds mainly cause precipitation, influenced by water vapor from the Amazon and enhanced easterlies during boreal summer. TM regions are transition zones from UM to BM and zones on the windward slopes of the western cordillera. These results highlight the suitability of satellite and GIS data-driven statistical models to study spatiotemporal rainfall seasonality and generation processes in complex terrain, as the Andes

A research framework for projecting ecosystem change in highly diverse tropical mountain ecosystems

Tropical mountain ecosystems are threatened by climate and land-use changes. Their diversity and complexity make projections how they respond to environmental changes challenging. A suitable way are trait-based approaches, by distinguishing between response traits that determine the resistance of species to environmental changes and effect traits that are relevant for species\u27 interactions, biotic processes, and ecosystem functions. The combination of those approaches with land surface models (LSM) linking the functional community composition to ecosystem functions provides new ways to project the response of ecosystems to environmental changes. With the interdisciplinary project RESPECT, we propose a research framework that uses a trait-based response-effect-framework (REF) to quantify relationships between abiotic conditions, the diversity of functional traits in communities, and associated biotic processes, informing a biodiversity-LSM. We apply the framework to a megadiverse tropical mountain forest. We use a plot design along an elevation and a land-use gradient to collect data on abiotic drivers, functional traits, and biotic processes. We integrate these data to build the biodiversity-LSM and illustrate how to test the model. REF results show that aboveground biomass production is not directly related to changing climatic conditions, but indirectly through associated changes in functional traits. Herbivory is directly related to changing abiotic conditions. The biodiversity-LSM informed by local functional trait and soil data improved the simulation of biomass production substantially. We conclude that local data, also derived from previous projects (platform Ecuador), are key elements of the research framework. We specify essential datasets to apply this framework to other mountain ecosystems

The state of the Martian climate

60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes

State of the climate in 2018

In 2018, the dominant greenhouse gases released into Earth’s atmosphere—carbon dioxide, methane, and nitrous oxide—continued their increase. The annual global average carbon dioxide concentration at Earth’s surface was 407.4 ± 0.1 ppm, the highest in the modern instrumental record and in ice core records dating back 800 000 years. Combined, greenhouse gases and several halogenated gases contribute just over 3 W m−2 to radiative forcing and represent a nearly 43% increase since 1990. Carbon dioxide is responsible for about 65% of this radiative forcing. With a weak La Niña in early 2018 transitioning to a weak El Niño by the year’s end, the global surface (land and ocean) temperature was the fourth highest on record, with only 2015 through 2017 being warmer. Several European countries reported record high annual temperatures. There were also more high, and fewer low, temperature extremes than in nearly all of the 68-year extremes record. Madagascar recorded a record daily temperature of 40.5°C in Morondava in March, while South Korea set its record high of 41.0°C in August in Hongcheon. Nawabshah, Pakistan, recorded its highest temperature of 50.2°C, which may be a new daily world record for April. Globally, the annual lower troposphere temperature was third to seventh highest, depending on the dataset analyzed. The lower stratospheric temperature was approximately fifth lowest. The 2018 Arctic land surface temperature was 1.2°C above the 1981–2010 average, tying for third highest in the 118-year record, following 2016 and 2017. June’s Arctic snow cover extent was almost half of what it was 35 years ago. Across Greenland, however, regional summer temperatures were generally below or near average. Additionally, a satellite survey of 47 glaciers in Greenland indicated a net increase in area for the first time since records began in 1999. Increasing permafrost temperatures were reported at most observation sites in the Arctic, with the overall increase of 0.1°–0.2°C between 2017 and 2018 being comparable to the highest rate of warming ever observed in the region. On 17 March, Arctic sea ice extent marked the second smallest annual maximum in the 38-year record, larger than only 2017. The minimum extent in 2018 was reached on 19 September and again on 23 September, tying 2008 and 2010 for the sixth lowest extent on record. The 23 September date tied 1997 as the latest sea ice minimum date on record. First-year ice now dominates the ice cover, comprising 77% of the March 2018 ice pack compared to 55% during the 1980s. Because thinner, younger ice is more vulnerable to melting out in summer, this shift in sea ice age has contributed to the decreasing trend in minimum ice extent. Regionally, Bering Sea ice extent was at record lows for almost the entire 2017/18 ice season. For the Antarctic continent as a whole, 2018 was warmer than average. On the highest points of the Antarctic Plateau, the automatic weather station Relay (74°S) broke or tied six monthly temperature records throughout the year, with August breaking its record by nearly 8°C. However, cool conditions in the western Bellingshausen Sea and Amundsen Sea sector contributed to a low melt season overall for 2017/18. High SSTs contributed to low summer sea ice extent in the Ross and Weddell Seas in 2018, underpinning the second lowest Antarctic summer minimum sea ice extent on record. Despite conducive conditions for its formation, the ozone hole at its maximum extent in September was near the 2000–18 mean, likely due to an ongoing slow decline in stratospheric chlorine monoxide concentration. Across the oceans, globally averaged SST decreased slightly since the record El Niño year of 2016 but was still far above the climatological mean. On average, SST is increasing at a rate of 0.10° ± 0.01°C decade−1 since 1950. The warming appeared largest in the tropical Indian Ocean and smallest in the North Pacific. The deeper ocean continues to warm year after year. For the seventh consecutive year, global annual mean sea level became the highest in the 26-year record, rising to 81 mm above the 1993 average. As anticipated in a warming climate, the hydrological cycle over the ocean is accelerating: dry regions are becoming drier and wet regions rainier. Closer to the equator, 95 named tropical storms were observed during 2018, well above the 1981–2010 average of 82. Eleven tropical cyclones reached Saffir–Simpson scale Category 5 intensity. North Atlantic Major Hurricane Michael’s landfall intensity of 140 kt was the fourth strongest for any continental U.S. hurricane landfall in the 168-year record. Michael caused more than 30 fatalities and $25 billion (U.S. dollars) in damages. In the western North Pacific, Super Typhoon Mangkhut led to 160 fatalities and$6 billion (U.S. dollars) in damages across the Philippines, Hong Kong, Macau, mainland China, Guam, and the Northern Mariana Islands. Tropical Storm Son-Tinh was responsible for 170 fatalities in Vietnam and Laos. Nearly all the islands of Micronesia experienced at least moderate impacts from various tropical cyclones. Across land, many areas around the globe received copious precipitation, notable at different time scales. Rodrigues and Réunion Island near southern Africa each reported their third wettest year on record. In Hawaii, 1262 mm precipitation at Waipā Gardens (Kauai) on 14–15 April set a new U.S. record for 24-h precipitation. In Brazil, the city of Belo Horizonte received nearly 75 mm of rain in just 20 minutes, nearly half its monthly average. Globally, fire activity during 2018 was the lowest since the start of the record in 1997, with a combined burned area of about 500 million hectares. This reinforced the long-term downward trend in fire emissions driven by changes in land use in frequently burning savannas. However, wildfires burned 3.5 million hectares across the United States, well above the 2000–10 average of 2.7 million hectares. Combined, U.S. wildfire damages for the 2017 and 2018 wildfire seasons exceeded $40 billion (U.S. dollars)

Atmospheric Moisture Pathways to the Highlands of the Tropical Andes: Analyzing the Effects of Spectral Nudging on Different Driving Fields for Regional Climate Modeling

Atmospheric moisture pathways to the highlands of the tropical Andes Mountains were investigated using the Weather Research and Forecasting (WRF) model, as well as back-trajectory analysis. To assess model uncertainties according to the initial and lateral boundary conditions (ILBCs), the effects of spectral nudging and different driving fields on regional climate modeling were tested. Based on the spatio-temporal patterns of the large-scale atmospheric features over South America, the results demonstrated that spectral nudging compared to traditional long-term integration generally produced greater consistency with the reference data (ERA5). These WRF simulations further revealed that the location of the inter-tropical convergence zone (ITCZ), as well as the precipitation over the Andes Mountains were better reproduced. To investigate the air mass pathways, the most accurate WRF simulation was used as atmospheric conditions for the back-trajectory calculations. Three subregions along the tropical Andean chain were considered. Based on mean cluster trajectories and the water vapor mixing ratio along the pathways, the contributions of eastern and western water sources were analyzed. In particular, the southernmost subregion illustrated a clear frequency of occurrences of Pacific trajectories mostly during September⁻November (40%) when the ITCZ is shifted to the Northern Hemisphere and the Bolivian high pressure system is weakened. In the northernmost subregion, Pacific air masses as well reached the Andes highlands with rather low frequencies regardless of the season (2⁻12%), but with a moisture contribution comparable to the eastern trajectories. Cross-sections of the equivalent-potential temperature as an indicator of the moisture and energy content of the atmosphere revealed a downward mixing of the moisture aloft, which was stronger in the southern subregion. Additionally, low-level onshore breezes, which developed in both subregions, indicated the transport of warm-moist marine air masses to the highlands, highlighting the importance of the representation of the terrain and, thus, the application of dynamical downscaling using regional climate models

Cold Air Drainage Flows and their Relation to the Formation of Nocturnal Convective Clouds at the Eastern Andes of South Ecuador

The development of clouds has many causes, not all of those are examined. In consideration of rainfall behaviour and distribution knowledge of cloud formation, processes in the tropics are of particular importance. Clouds are part of the hydrological cycle, influencing water resources and the energy budget. The insight into unknown cloud generation processes is a great benefit in the developmental procedure of understanding the structure and functionality of an ecosystem and its biodiversity. The main objective of the presented study was to investigate an unidentified nocturnal cloud formation procedure in the eastern Andes of South Ecuador and the adjacent northern Peruvian Amazon. The central theses encompass the confluence of katabatic flows in highly complex terrain due to a concave configuration. This cold drainage of air induces a surface cold front in the foothills of the eastern Andes, which initiates moisture convection due to compressional lifting by the terrain; a nocturnal LLJ triggers the development of the MCS. For the evaluation of the hypotheses the numerical model ARPS was used to analyse the not fully understood highland - lowland interactions in the PBL. At first, simulations of an accurate katabatic flow and its behaviour in complex terrain were performed with optimal conditions and without location information. The main subject of the study was the confluence of the cold drainage of air as a result of concave-lined terrain. Simplified DEMs, inspired by the Andes, were used for this analysis, due to the very steep slopes and valleys of the real terrain. A stepwise increase in their complexity, beginning with a simple slope, enabled the examination of the impact of the terrain configuration on the flow’s dynamic behaviour. With the most complex terrain model, which represents a concave ridgeline interrupted by several valleys draining into a basin, the confluence of the downslope flows due to the geometry of the terrain was demonstrated. Thus, a representative, persistent, thermally driven flow was generated, creating a convergence line that was largest in the centre of the basin. Afterwards, a simulation of a katabatically induced surface cold front with subsequent convective cloud formation was performed with the same model framework, except for the atmospheric water vapour. The simulation showed the same confluence of the downslope flows with a convergence line inside the basin as before. The development of a katabatically induced cold front was identified based on characteristic attributes described in chapter 2 using a cross-section through this line. Furthermore, the results also showed a convergence line that was largest in the centre of the basin. Because of the initiation of moisture convection in this area, due to sufficient moisture in the atmosphere, it was evident that the terrain geometry was the triggering mechanism for cloud formation. The presence of an LLJ in the basin showed the intensification of the cloud formation process. However, the previous results showed that the cluster developed primarily due to compressional lifting by the terrain. This shows that the LLJ had marginal effects on the initiation of moisture convection, acting primarily as an enhancement of its occurrence. Finally, the spatial reference was enabled and the parametrisation set-up of the idealised studies was assigned and adjusted to a multi-nested, approximately realistic model setting, strengthening the evidence from the previous results. For the study, a specific situation, selected on the basis of GOES-E satellite data was used. The main subject was the demonstration of the development of an MCS in the foothills of the eastern Andes due to the presence of katabatic flows as the driving mechanism. The GOES-E brightness temperatures were used to compare the satellite-observed data with the ARPS data to verify the simulated cloud appearance. Due to the fact that the 4 km domain revealed no convective clouds, but a convective cloud cluster was generated on the 1 km domain, a scale dependency was determined. This was caused by two factors: first of all, the NBL processes were simulated more accurately due to the higher vertical resolution, thus more accurately representing the katabatic flows. Furthermore, the higher resolved domain represented a more structured terrain, resulting in stronger convergences of the downslope flows. The comparison of the satellite and the modelled data presented a good agreement concerning the orientation, the location as well as the cold tops of the cells. A closer look at the NBL revealed cold air drainage, nourishing the cell regeneration. The typical characteristics, discussed in the idealised study without location information, confirmed the occurrence of thermally induced downslope flows as the driving process behind convective initiation