ALBERT

Description: [1]  Mountain rivers play a key role in the delivery of particulate organic carbon (POC) to large river systems and the ocean. Due to the extent of its drainage area and runoff, the Amazon River is one of Earth's most important biogeochemical systems. However the source of POC eroded from the humid region of the Eastern Andes and the input of fossil POC from sedimentary rocks (POC fossil ) remains poorly constrained. Here we collected suspended sediments from the Kosñipata River during flood events to better characterise Andean POC, measuring the nitrogen to organic carbon ratio (N/C), stable carbon isotopes ( δ 13 C org ) and radiocarbon ( Δ 14 C org ). Δ 14 C org values ranged from -711‰ to -15‰ and significant linear trends between Δ 14 C org, N/C and δ 13 C org suggested that this reflects the mixing of POC fossil with very young organic matter ( Δ 14 C org  ~ 50‰) from the terrestrial biosphere (POC non-fossil ). Using N/C and Δ 14 C org in an end member mixing analysis, we quantify the fraction of POC fossil (to within 0.1) and find that it contributes a constant proportion of the suspended sediment mass (0.37 ± 0.03%) and up to 80% of total POC. In contrast, the relative contribution of POC non-fossil was variable, being most important during the rising limb and peak discharges of flood-events. The new data shed light on published measurements of ‘old’ POC (low Δ 14 C org ) in Andean-fed tributaries of the Amazon River, with their Δ 14 C org and δ 13 C org values consistent with variable addition of POC fossil . The findings suggest a greater persistence of Andean POC in the lowland Amazon than previously recognised.

Description: ABSTRACT The South Asian summer monsoon (SASM) exhibits large variability in the intraseasonal scale, and active and break cycles of monsoon constitute dominant mode of this variability. This has been subject of many model-based studies as improved simulation of intraseasonal features also leads to better representation of the seasonal mean characteristics. We evaluate a recent Hadley centre regional climate model's performance, at low and high resolutions and forced by a reanalysis, in simulating various characteristics associated with intraseasonal variability of SASM. In particular, we compare the spatial patterns of precipitation and upper level circulation composites for active and break spells and, timing, frequency and duration of those spells. We found improvements in simulation of active and break composite precipitation in the high-resolution simulation. These improvements probably come from improved position of the monsoon trough particularly over west India for active composite and improved low-level flow particularly south of the Himalaya for break composite. Moreover, enhanced capacity of the model at high resolution to resolve atmospheric motions and interaction of moisture laden low-level flow with the steep Himalayan orography is likely to contribute in reduction of excess precipitation over Indo-Gangetic plain. Similarly, improvements over east Nepal for break spells are likely to come from model's ability to effectively capture precipitation enhancements that arise from orographic-forced and mid-tropospheric ascending motions. However, mixed results are obtained for temporal statistics associated with occurrence of active and break events. We also compare the model performance in simulating precipitation extremes over Nepal. The timing of extreme precipitation occurrence in relation to peak monsoon months and break spells, and contribution of the extreme cumulative precipitation to the seasonal total are improved in the high-resolution simulation.

Description: Global climate models suggest enhanced warming of the tropical mid and upper troposphere, with larger temperature rise rates at higher elevations. Changes in fire activity are amongst the most significant ecological consequences of rising temperatures and changing hydrological properties in mountainous ecosystems, and there is global evidence of increased fire activity with elevation. Whilst fire research has become popular in the tropical lowlands, much less is known of the tropical high Andean region (〉2000masl, from Colombia to Bolivia). This study examines fire trends in the high Andes for three ecosystems, the Puna, the Paramo and the Yungas, for the period 1982-2006. We pose three questions: 1) is there an increased fire response with elevation? ii) does the El Niño- Southern Oscillation control fire activity in this region? iii) are the observed fire trends human driven (e.g. human practices and their effects on fuel build-up) or climate driven? We did not find evidence of increased fire activity with elevation but, instead, a quasi-cyclic and synchronous fire response in Ecuador, Peru and Bolivia, suggesting the influence of high frequency climate forcing on fire responses on a subcontinental scale, in the high Andes. ENSO variability did not show a significant relation to fire activity for these three countries, partly because ENSO variability did not significantly relate to precipitation extremes, although it strongly did to temperature extremes. Whilst ENSO did not individually lead the observed regional fire trends, our results suggest a climate influence on fire activity, mainly through a sawtooth pattern of precipitation (increased rainfall before fire peak seasons (t-1) followed by drought spells and unusual low temperatures (t0), which is particular common where fire is carried by low fuel loads (e.g. grasslands and fine fuel). This climatic sawtooth appeared as the main driver of fire trends, above local human influences and fuel build-up cyclicity. This article is protected by copyright. All rights reserved.

Description: This study examines for the first time the changing characteristics of summer and winter southern African rainfall, and their teleconnections with large-scale climate through the dominant timescales of variability. As determined by wavelet analysis, the austral summer and winter rainfall indices exhibit three significant timescales of variability over the 20 th century: interdecadal (15–28 year), quasi-decadal (8–13 year) and interannual (2–8 year). Teleconnections with global sea-surface temperature and atmospheric circulation anomalies are established here, but are different for each timescale. Tropical/subtropical teleconnections emerge as the main driver of austral summer rainfall variability. Thus, shifts in the Walker circulation are linked to the El Niño Southern Oscillation (ENSO) and, at decadal timescales, to decadal ENSO-like patterns related to the Pacific Decadal Oscillation and the Interdecadal Pacific Oscillation. These global changes in the upper-zonal circulation interact with asymmetric ocean-atmospheric conditions between the South Atlantic and South Indian Oceans; together these lead to shift in the South Indian Convergence Zone, and a modulation of the development of convective rain bearing systems over southern Africa in summer. Such regional changes, embedded in quasi-annular geopotential patterns, consist of easterly moisture fluxes from the South Indian High, which dominate southerly moisture fluxes from the South Atlantic High. Austral winter rainfall variability is more influenced by mid-latitude atmospheric variability, in particular the Southern Annular Mode. The rainfall changes in the southwestern regions of southern Africa are determined by asymmetrical changes in the mid-latitude westerlies between the Atlantic and Indian Oceans.

Description: [1]  The first results of a multi-sensor airborne survey conducted off the western Iberian Coast are presented (including visible, lidar, and infrared imagery), and reveal the presence of Internal Solitary Waves (ISWs) propagating into the near-shore region. For the first time, two-dimensional lidar imagery is shown to detect the presence of ISWs, and the results are interpreted in a more comprehensive framework provided by the remaining instrumentation. Sea surface roughness patterns resulting from the ISWs are found to be imaged in the lidar data, where specular reflection causes slicks to appear as areas of significantly reduced backscatter. Moreover, the lidar data reveals an unprecedented view into the ISWs surface and subsurface structure. Possible interpretations are discussed based on the accumulation of surfactants and air bubble entrainment at the leading edge of the ISWs (where maximum convergence occurs).

Description: ABSTRACT The South Asian summer monsoon (SASM) is a continental scale weather phenomenon, which fluctuates at a range of temporal and spatial scales. Although majority of global climate models are broadly able to simulate the large scale characteristics of the SASM, they generally have major deficiencies such as constraints in reproducing observed mean precipitation. It is generally anticipated that higher resolution regional climate models (RCMs) would be able to simulate an improved mean state owing to their capacity to better simulate fine temporal and spatial scale features and variability. Here, we analyse SASM simulations using a contemporary Hadley Centre RCM, forced by ERA-Interim reanalysis and observed sea surface temperature, at medium (0.44°) and high (0.11°) horizontal resolutions. Evaluation of the results show that, compared to the medium resolution RCM, the high resolution RCM is able to better resolve the interaction of the low level monsoon flow with the Himalayan orography leading to added value in simulating many aspects of SASM precipitation such as the seasonal mean, relative frequency distribution of daily precipitation, and various metrics of precipitation extremes. In contrast to many previous studies, maximum added value is note along the Indo-Gangetic plain rather than over the complex Himalayas, and the added values of up to 5 mm day −1 and 50 days are noted for mean precipitation and number of wet days, respectively over the region. Similarly, added values of up to 15 and 3 mm day −1 are noted for 95th percentile of daily precipitation and simple daily intensity index, respectively over central India and the Himalayan range. These results suggest that higher resolution RCMs have the potential to add more value when downscaling global climate model climate change projections.

Description: [1]  The climate and ecology of tropical montane systems is intimately connected with the complex spatial dynamics of cloud occurrence, but there have been few studies of the patterns and trends of cloud occurrence in tropical montane regions. We examine trends and variability in the cloud climatology of the Andes/Amazon transition in SW Amazonia using satellite data and ground-based observations. Results were compared for three zones within the study area: highlands (puna grassland), eastern slope (Tropical Montane Cloud Forest or TMCF) and lowlands. Time series of cloud frequency from ISCCP (International Satellite Cloud Climatology Project) were correlated with sea surface temperature (SST) anomalies from the HadISST data set for 5 regions including the tropical North Atlantic and the tropical Pacific. Detrended lowland cloud frequencies were significantly correlated with detrended tropical North Atlantic SSTs in the late dry season (August/September), whereas the eastern slope and the highlands were not significantly correlated with tropical North Atlantic SSTs. Pacific SST correlations were highest for eastern slope and highlands from March to May. Indian Ocean SST anomalies were significantly correlated with dry season cloud frequency for the lowlands and highlands. There are significant decreasing trends in cloud frequency on the lowlands in January, March and September and in March on the eastern slope. Trends in sunshine duration, 850 hPa zonal winds over the central Amazon, increases in diurnal temperature range, and comparisons with MODIS (Moderate Resolution Imaging Spectroradiometer) and observational data support the existence of these trends, and a link with the increasing trend in tropical North Atlantic SSTs. We suggest that continued increases in tropical North Atlantic SSTs will further reduce cloud frequency in the lowlands adjacent to the TMCF in the late dry season at least. In addition, a future increase in the occurrence of El Niño events would lead to decreased cloud frequency on the eastern slope and highlands.

Description: [1]  Tropical montane regions present a complex local climate but one that may be very sensitive to local and global change. Therefore, it is important to assess their current climatological state, and to understand how the large-scale circulation may affect local-scale cloud patterns. We examine the cloud climatology of a tropical Andean montane region in the context of tropical South American climate in terms of seasonal/diurnal cycles using a corrected ISCCP (International Satellite Cloud Climatology Project) DX cloud product (1983–2008), MODIS (Moderate Resolution Imaging Spectroradiometer) MOD35 visible cloud flags (2000–2008) and ground-based cloud observations. Cloud climatologies were compared for three elevation zones: highlands (puna grassland), eastern slope (the montane forest) and lowlands. We found that in the dry season (JJA) the study area is part of a localized region of higher cloud frequency relative to other parts the eastern slope, and also relative to the adjacent highlands and lowlands. The highlands exhibited the greatest amplitude mean annual cycle of cloud frequency, with a minimum in June for all times of day. There were contrasts between the three zones with regard to the month in which the minimum cloud frequency occurs between different times of day. Higher lowland and eastern slope cloud frequencies compared with those on the puna in the early hours in the wet season suggest low-level convergence at lower elevations. Comparisons between satellite products show that ISCCP and MODIS produce very similar annual cycles although the absolute cloud frequencies are higher in ISCCP data.

Description: The climate and ecology of tropical montane systems is intimately connected with the complex spatial dynamics of cloud occurrence, but there have been few studies of the patterns and trends of cloud occurrence in tropical montane regions. We examine trends and variability in the cloud climatology of the Andes/Amazon transition in SW Amazonia using satellite data and ground-based observations. Results were compared for three zones within the study area: highlands (puna grassland), eastern slope (Tropical Montane Cloud Forest or TMCF) and lowlands. Time series of cloud frequency from ISCCP (International Satellite Cloud Climatology Project) were correlated with sea surface temperature (SST) anomalies from the HadISST data set for 5 regions including the tropical North Atlantic and the tropical Pacific. Detrended lowland cloud frequencies were significantly correlated with detrended tropical North Atlantic SSTs in the late dry season (August/September), whereas the eastern slope and the highlands were not significantly correlated with tropical North Atlantic SSTs. Pacific SST correlations were highest for eastern slope and highlands from March to May. Indian Ocean SST anomalies were significantly correlated with dry season cloud frequency for the lowlands and highlands. There are significant decreasing trends in cloud frequency on the lowlands in January, March and September and in March on the eastern slope. Trends in sunshine duration, 850 hPa zonal winds over the central Amazon, increases in diurnal temperature range, and comparisons with MODIS (Moderate Resolution Imaging Spectroradiometer) and observational data support the existence of these trends, and a link with the increasing trend in tropical North Atlantic SSTs. We suggest that continued increases in tropical North Atlantic SSTs will further reduce cloud frequency in the lowlands adjacent to the TMCF in the late dry season at least. In addition, a future increase in the occurrence of El Niño events would lead to decreased cloud frequency on the eastern slope and highlands.