Regional climatic effects according to different estimations of biogenic volatile organic compounds during the asian summer monsoon

A series of 60-year numerical experiments starting from 1851 was conducted using a global climate model coupled with an aerosol-cloud-radiation model to investigate the response of the Asian summer monsoon to variations in the secondary organic aerosol (SOA) flux induced by two different estimations of biogenic volatile organic compound (BVOC) emissions. One estimation was obtained from a pre-existing archive and the other was generated by a next-generation model (the Model of Emissions of Gases and Aerosols from Nature, MEGAN). The use of MEGAN resulted in an overall increase of the SOA production through a higher rate of gasto-particle conversion of BVOCs. Consequently, the atmospheric loading of organic carbon (OC) increased due to the contribution of SOA to OC aerosol. The increase of atmospheric OC aerosols was prominent in particular in the Indian subcontinent and Indochina Peninsula (IP) during the pre- and early-monsoon periods because the terrestrial biosphere is the major source of BVOC emissions and the atmospheric aerosol concentration diminishes rapidly with the arrival of monsoon rainfall. As the number of atmospheric OC particles increased, the number concentrations of cloud droplets increased, but their size decreased. These changes represent a combination of aerosol-cloud interactions that were favorable to rainfall suppression. However, the modeled precipitation was slightly enhanced in May over the oceans that surround the Indian subcontinent and IP. Further analysis revealed that a compensating updraft in the surrounding oceans was induced by the thermally-driven downdraft in the IP, which was a result of surface cooling associated with direct OC aerosol radiative forcing, and was able to surpass the aerosolcloud interactions. The co-existence of oceanic ascending motion with the maximum convective available potential energy was also found to be crucial for rainfall formation. Although the model produced statistically significant rainfall changes with locally organized patterns, the suggested pathways should be considered guardedly because in the simulation results, 1) the BVOC-induced aerosol direct effect was marginal; 2) cloud-aerosol interactions were modeldependent; and 3) Asian summer monsoons were biased to a nonnegligible extent.     

Interpretation of El Niño–Southern Oscillation‐related precipitation anomalies in north‐western Borneo using isotopic tracers

We examined rainfall anomalies associated with the El Niño–Southern Oscillation (ENSO) in northern Sarawak, Malaysia, using the oxygen isotopic composition of rainfall. Two precipitation‐sampling campaigns were conducted for isotope analysis: (a) at the Lambir Hill National Park (4.2° N, 114.0° E) from July 2004 to October 2006 and (b) at the Gunung Mulu National Park (3.9° N, 114.8° E) from January 2006 to July 2008. The records from these campaigns were merged with a previously published rainfall isotope dataset from Gunung Mulu site to create a 7‐year‐long record of the oxygen isotopic composition of Sarawak rainfall. The record exhibits clear intraseasonal variations (ISVs) with periods ranging from 10 to 70 days. The ISVs of 10‐ to 90‐day band‐pass filtered oxygen isotopic composition are linked to the synoptic‐scale precipitation anomalies over the southern South China Sea (SCS). The lead–lag correlation map of precipitation with the filtered oxygen isotope anomalies shows that an anomalous wet condition responsible for the decrease in oxygen isotopic composition appears over the SCS in association with the passage of north‐eastward propagation of the boreal summer intraseasonal oscillation (BSISO) in the summer monsoon season. The anomalous wet condition in spring is connected with eastward‐propagating Madden–Julian oscillation (MJO), whereas the sustained wet condition in winter is responsible for the occurrence of the Borneo vortex (BV) over the SCS. ENSO modulates the frequency of these synoptic conditions on a seasonal and longer time scale, showing a strong correlation between the seasonal isotopic anomalies and the Southern Oscillation index. We therefore discern, from the significant correlation between the isotope anomalies and area‐averaged Sarawak rainfall anomalies (R = ?0.65, p < 0.01), that ENSO‐related precipitation anomalies are linked to the seasonal modulation of the BSISO and MJO activity and BV genesis.     

Light-absorbing particles in snow and ice: Measurement and modeling of climatic and hydrological impact

Light absorbing particles(LAP, e.g., black carbon, brown carbon, and dust) influence water and energy budgets of the atmosphere and snowpack in multiple ways. In addition to their effects associated with atmospheric heating by absorption of solar radiation and interactions with clouds, LAP in snow on land and ice can reduce the surface reflectance(a.k.a., surface darkening), which is likely to accelerate the snow aging process and further reduces snow albedo and increases the speed of snowpack melt. LAP in snow and ice(LAPSI) has been identified as one of major forcings affecting climate change, e.g.in the fourth and fifth assessment reports of IPCC. However, the uncertainty level in quantifying this effect remains very high. In this review paper, we document various technical methods of measuring LAPSI and review the progress made in measuring the LAPSI in Arctic, Tibetan Plateau and other mid-latitude regions. We also report the progress in modeling the mass concentrations, albedo reduction, radiative forcing, and climatic and hydrological impact of LAPSI at global and regional scales. Finally we identify some research needs for reducing the uncertainties in the impact of LAPSI on global and regional climate and the hydrological cycle.     

Dynamics of distinct intraseasonal oscillation in summer monsoon rainfall over the Meghalaya–Bangladesh–western Myanmar region: covariability between the tropics and mid-latitudes

Detailed spatiotemporal structures for the submonthly-scale (7–25 days) intraseasonal oscillation (ISO) in summer monsoon rainfall and atmospheric circulation were investigated in South Asia using high-quality rainfall and reanalysis datasets. The Meghalaya–Bangladesh–coast of the western Myanmar (MBWM) region is the predominant area of submonthly-scale ISO in the Asian monsoon regions. The distinct rainfall ISO is caused by a remarkable alternation of low-level zonal wind between westerly and easterly flows around the Gangetic Plain on the same timescales. In the active ISO phase of the MBWM, a strong low-level westerly/southwesterly flows around the plain and a center of cyclonic vorticity appears over Bangladesh. Hence, a local southerly flows toward the Meghalaya Plateau and there is strong southwesterly flow towards the coast along southeastern Bangladesh and western Myanmar, resulting in an increase in orographic rainfall. Rainfall also increases over the lowland area of the MBWM due to the low-level convergence in the boundary layer under the strong cyclonic circulation. The submonthly-scale low-level wind fluctuation around the MBWM is caused by a westward moving n = 1 equatorial Rossby (ER) wave. When the anticyclonic (cyclonic) anomaly related to the ER wave approaches the Bay of Bengal from the western Pacific, humid westerly/southwesterly (easterly/southeasterly) flows enhance around the Gangetic Plain on the northern fringe of the anticyclone (cyclone) and in turn promote (reduce) rainfall in the MBWM. Simultaneously, robust circulation signals are observed over the mid-latitudes. In the active phase, cyclonic anomalies appear over and around the TP, having barotropic vertical structure and also contributing to the enhancement of low-level westerly flow around the Gangetic Plain. In the upper troposphere, an anticyclonic anomaly is also observed upstream of the cyclonic anomaly over the TP, having wavetrain structure. The mid-latitude circulation around the TP likely helps to induce the distinct ISO there in conjunction with the equatorial waves. Thus, the distinct ISO in the MBWM is strongly enhanced locally (~500 km) by the terrain features, although the atmospheric circulation causing the ISO has a horizontal scale of ~6,000 km or more, extending across the whole Asian monsoon system from the tropics to mid-latitudes.     

Simulated changes in the atmospheric water balance over South Asia in the eight IPCC AR4 coupled climate models

This paper evaluates the performance of eight state-of-art IPCC-AR4 coupled atmosphere-ocean general circulation models in their representation of regional characteristics of atmospheric water balance over South Asia. The results presented here are the regional climate change scenarios of atmospheric water balance components, precipitation, moisture convergence and evaporation (P, C and E) up to the end of the twenty-second century based on IPCC AR4 modelling experiments conducted for (A1B) future greenhouse gas emission scenario. The AOGCMs, despite their relatively coarse resolution, have shown a reasonable skill in depicting the hydrological cycle over the South Asian region. However, considerable biases do exist with reference to the observed atmospheric water balance and also inter-model differences. The monsoon rainfall and atmospheric water balance changes under A1B scenario are discussed in detail. Spatial patterns of rainfall change projections indicate maximum increase over northwest India in most of the models, but changes in the atmospheric water balance are generally widespread over South Asia. While the scenarios presented in this study are indicative of the expected range of rainfall and water balance changes, it must be noted that the quantitative estimates still have large uncertainties associated with them.     

春季亚洲地面湿度异常对月、季气候影响的模拟研究

通过大气环流模式试验,研究了春季亚洲中纬带地面湿度异常对其后4个月月平均气候参数的影响.结果发现:正的地面湿度异常对其后气候参数的影响在第1个月最弱,第3个月最强;它导致欧亚中高纬带在第2～4个月对流层内的高度和温度都降低,低值系统发展,副热带高压亦发展,中纬度西风急流相应增强;同时北美东岸有明显的遥相关响应.     

Cretaceous climate oscillations in the southern palaeolatitudes: New stable isotope evidence from India and Madagascar

Palaeotemperatures for the Cretaceous of India and Madagascar have been determined on the basis of oxygen isotopic analysis of well-preserved Albian belemnite rostra and Maastrichtian bivalve shells of from the Trichinopoly district, southern India, and Albian nautiloid and ammonoid cephalopods from the Mahajang Province, Madagascar. The Albian (possibly late Albian) palaeotemperatures for Trichinopoly district are inferred to range from 14.9 °C to 18.5 °C for the epipelagic zone, and from 14.3 °C to 15.9 °C for the mesopelagic zone, based on analyses of 65 samples; isotopic palaeotemperatures interpreted as summer and winter values for near-bottom shelf waters in this area fluctuate from 16.3 to 18.5 °C and from 14.9 to 16.1 °C, respectively. The mentioned palaeotemperatures are very similar to those calculated from isotopic composition of middle Albian belemnites of the middle latitude area of Pas-de-Calais in Northern hemisphere but significantly higher than those calculated from isotopic composition of Albian belemnites from southern Argentina and the Antarctic and middle Albian belemnites of Australia located within the warm-temperate climatic zone. Isotopic analysis of early Albian cephalopods from Madagascar shows somewhat higher palaeotemperatures for summer near-bottom shelf waters in this area (20.2-21.6 °C) in comparison with late Albian palaeotemperatures calculated from southern India fossils, but similar winter values (13.3-16.4 °C); however, the latter values are somewhat higher than those calculated from early Albian ammonoids of the tropical-subtropical climatic zone of the high latitude area of southern Alaska and the Koryak Upland. The new isotopic palaeotemperature data suggest that southern India and Madagascar were located apparently in middle latitudes (within the tropical-subtropical climatic zone) during Albian time. In contrast to the Albian fossils, isotope results of well-preserved early Maastrichtian bivalve shells from the Ariyalur Group, Trichinopoly district, are characterised by lower δ¹⁸O values (up to −5.8‰) but normal δ¹³C values, which might be a result local freshwater input into the marine environment. Our data suggest that the early Maastrichtian palaeotemperature of the southern Indian near-bottom shelf waters was probably about 21.2 °C, and that this middle latitude region continued to be a part of tropical-subtropical climatic zone, but with tendency of increasing of humidity at the end of Cretaceous time.     

Palaeotemperature curve for the Late Cretaceous of the northwestern circum-Pacific

In the northwestern circum-Pacific, two main trends in Late Cretaceous temperatures can be recognized. (1) In general, a recurrent warming trend is thought to have begun in the Turonian–Campanian, reaching temperature maxima in the early Late Santonian and early Late Campanian, and temperature minima in the earliest Santonian and perhaps early Campanian. (2) During the Maastrichtian, temperatures dropped sharply, with only a slight warming in the early Late Maastrichtian. The existence of a thermal maximum at the Coniacian–Santonian transition has previously been expected, but is not confirmed by new isotopic results.     

Vertical Distributions of Larvae of the Clam <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis> and the Striped Horse Mussel <Emphasis Type="Italic">Musculista senhousia</Emphasis> in Eastern Ariake Bay,Southern Japan

We have examined the vertical distributions of planktonic bivalve larvae, particularly the clam Ruditapes philippinarum and the mussel Musculista senhousia which are common and abundant on tidal flats of eastern Ariake Bay, southern Japan. Submersible pumping gear was used to take samples at 2 stations every 2 hours during the spring tide over a whole tidal cycle and/or through daytime and nighttime. Water samples were pumped up from 3 to 5 depths from the surface to sea bottom. Regardless of tidal cycles, D-shaped larvae were concentrated near the surface, while umbo larvae were found at the surface to intermediate depths. On average, these larval densities were significantly higher at the station close to the shore than the offshore station, with no significant difference between daytime and nighttime and between flood and ebb tides at each station. The velocity and direction of water movement at both stations revealed remarkable difference between the surface and bottom waters. The larvae at the surface may quickly disperse and be transported elsewhere, while those in water close to the sea bottom may tend to be retained.