Diurnal variation of outgoing longwave radiation derived from I NSA T-I B data

In this paper, 3-hourly values of Outgoing Long wave Radiation (OLR) for the years 1987 .to 1990 over the Indian Ocean region, derived from'1NSAT-IB VHRR observations, have been used to study the patterns of diurnal variation of OLR. The nature of the diurnal variations over different regions such as desert, ocean, monsoon area and equatorial trough in four representative months of the year is discussed. The variations in the diurnal range of OLR and the hours of occurrence of OLR minimum and maximum, are also presented.Daily means of TNSAT OLR using all.eight 3-hour samples and four different pairs of. 12-hour samples were computed. Results show that they are highly correlated. However, averages made with OLR values corresponding to 0230 and 1430 local time are slight underestimates compared to the 8-sample averages, whereas averages based upon 0830 and 2030 local time are slight overestimates.

Pastoralism and Millet Cultivation During the Bronze Age in the Temperate Steppe Region of Northern China

Eastern and Western Asia were important centers for the domestication of plants and animals and they developed different agricultural practices and systems. The timing, routeway and mechanisms of the exchanges between the two centers have long been important scientific issues. The development of a mixed pastoral system (e.g., with the rearing of sheep, goats and cattle) and millet cultivation in the steppe region of northern China was the result of the link between the two cultures. However, little detailed information is available about the precise timing and mechanisms involved in this mixture of pastoralism and millet cultivation. To try to address the issue, we analyzed the pollen, fungal spores and phytolith contents of soil samples from the Bronze Age Zhukaigou site in the steppe area of North China, which was combined with AMS 14C dating of charcoal, millet and animal bones. A mixed pastoralism and millet agricultural system appeared at the site between 4,000 and 3,700 cal yr BP, and the intensity of animal husbandry increased in the later stage of occupation. Published data indicate that domestic sheep/goats appeared across a wide area of the steppe region of northern China after ∼4,000 cal yr BP. A comparison of records of sheep/goat rearing and paleoclimatic records from monsoon area in China leads us to conclude that the mixture of pastoralism and millet cultivation was promoted by the occurrence of drought events during 4,200–4,000 cal yr BP. Moreover, we suggest that mixed rainfed agriculture and animal husbandry increased the adaptability and resilience of the inhabitants of the region which enabled them to occupy the relatively arid environment of the monsoon marginal area of northern China.

A National-Scale 1-km Resolution PM2.5 Estimation Model over Japan Using MAIAC AOD and a Two-Stage Random Forest Model

Satellite-based models for estimating concentrations of particulate matter with an aerodynamic diameter less than 2.5 μm (PM2.5) have seldom been developed in islands with complex topography over the monsoon area, where the transport of PM2.5 is influenced by both the synoptic-scale winds and local-scale circulations compared with the continental regions. We validated Multi-Angle Implementation of Atmospheric Correction (MAIAC) aerosol optical depth (AOD) with ground observations in Japan and developed a 1-km-resolution national-scale model between 2011 and 2016 to estimate daily PM2.5 concentrations. A two-stage random forest model integrating MAIAC AOD with meteorological variables and land use data was applied to develop the model. The first-stage random forest model was used to impute the missing AOD values. The second-stage random forest model was then utilised to estimate ground PM2.5 concentrations. Ten-fold cross-validation was performed to evaluate the model performance. There was good consistency between MAIAC AOD and ground truth in Japan (correlation coefficient = 0.82 and 74.62% of data falling within the expected error). For model training, the model showed a training coefficient of determination (R2) of 0.98 and a root mean square error (RMSE) of 1.22 μg/m3. For the 10-fold cross-validation, the cross-validation R2 and RMSE of the model were 0.86 and 3.02 μg/m3, respectively. A subsite validation was used to validate the model at the grids overlapping with the AERONET sites, and the model performance was excellent at these sites with a validation R2 (RMSE) of 0.94 (1.78 μg/m3). Additionally, the model performance increased as increased AOD coverage. The top-ten important predictors for estimating ground PM2.5 concentrations were day of the year, temperature, AOD, relative humidity, 10-m-height zonal wind, 10-m-height meridional wind, boundary layer height, precipitation, surface pressure, and population density. MAIAC AOD showed high retrieval accuracy in Japan. The performance of the satellite-based model was excellent, which showed that PM2.5 estimates derived from the model were reliable and accurate. These estimates can be used to assess both the short-term and long-term effects of PM2.5 on health outcomes in epidemiological studies.

Application of Dissolved Organic Carbon Runoff Model Considering Soil Infiltration and River Runoff Processes in Multiple Forested Watersheds

<p>Estimation of dissolved organic carbon (DOC) runoff load in forested watershed is important for the assessment of the global carbon cycle as well as for the control of regional water environments. A few process-based models have been proposed to estimate the DOC load to water environments, which assume DOC source in topsoil and transport processes to the river, however, these models exhibited difficulties with the availability of input data and applicability to short time-scale rainfall-runoff processes in the Asian monsoon area. This study presents a new process-based model that consists of two separate systems for determining DOC load enforced by DOC Source Area (DSA) concept. For the runoff system, a semi-distributed hydrological modelling unit (‘modified-TOPMODEL’) was installed, by which surface and subsurface water flows, representing for DSA, were sequentially simulated. For the soil system, a wet-dry cycle was successfully simulated by an advection-diffusion and dissolution formulation as well as seasonal temperature effect. The model is first evaluated upstream (98ha) and downstream (1798ha) in the Mizugaki Watershed, Yamanashi, Japan and then applied for a Miuchi (203ha) watershed, Aichi, Japan during 2014 to 2018. The results of cumulative DOC load at baseflow and stormflow periods that the model performed well between the simulations and observations for both study sites. Considering the stormflow periods, from 25.2% to 32.0%, and 31.1% of high flows contributed to 50% of the total DOC load at Mizugaki and Miuchi watershed, respectively. Overall, the proposed model successfully simulated DOC load under different geochemical and hydrological condition by capturing the DSA variability.</p>

Volcanic impact on the tropical hydrological cycle

<p>The impact of volcanic forcing on tropical precipitation is investigated in a new set of sensitivity experiments within Max Planck Institute Grand Ensemble framework. Five ensembles are created, each containing 100 realizations for an idealized tropical volcanic eruption located at the equator, analogous the Mt. Pinatubo eruption, with emissions covering a range of 2.5 - 40 Tg S. The ensembles provide an excellent database to disentangle the influence of volcanic forcing on regional monsoons and tropical hydroclimate over the wide spectrum of the climate internal variability. Monsoons are generally weaker during the two years after volcanic eruptions and their weakening is a function of emissions: the strongest the volcanic eruption, the weakest are the land monsoons. The extent of rain belt is also affected: the monsoon area is overall narrower than the unperturbed control simulation. While the position of main ascents does not change, the idealised tropical volcanic eruption supports the shrinking of Hadley Cell's ascent and the narrowing of the ITCZ. We investigate this behavior by analysing the changes in Hadley/Walker circulation, net energy input and energy budget to find analogies/differences with global warming.</p>

Evolution of the ocean monsoon regions over the past 250 million years

<p>A set of deep-time climate simulations each 10Ma years from 250Ma to PI are conducted by using the NCAR-CESM1.2, for understanding the evolution of the ocean monsoon regions driven by tectonic dynamics over the past 250 million years and exploring its variation mechanisms. In recent years, scientists have proposed the concept of a global monsoon system, which includes not only typical monsoon regions (such as the African monsoon region and South Asian monsoon region), but also the atypical Northwest Pacific Ocean monsoon region. Research on the ocean monsoon is very limited, especially in the field of paleoclimate. The results in this paper show that the horizontal gradients of the thickness of the ocean mixed layer may be more important for the formation of the ocean monsoon than land-sea thermal contrast, which is confirmed by the aquaplanet simulations with various gradients of the ocean mixed-layer thickness. Near the Pacific monsoon region in the northern hemisphere, the thickness of the ocean mixed layer has obvious meridional and zonal gradients, which will correspond to the meridional and zonal thermal contrasts. In addition, there are obvious seasonal reversals in the gradients of the ocean mixed-layer thickness in summer and winter, and the corresponding longitudinal and zonal thermal contrast produce seasonal reversals. Over the past 250 million years, the thickness of the ocean mixed layer on the east side of the Pacific Ocean Basin in the Northern Hemisphere has deepened, and the corresponding ocean monsoon area on the east side of the Pacific Ocean has decreased. The changes in the thickness of the ocean mixed layer are closely related to the changes in the surface wind field. Examining the changes in the atmospheric circulations, we find that the Pacific subtropical high strengthens and extends from east to the west bank of the ocean basin, where the atmospheric low-level anticyclonic circulation causes the ocean surface layer to converge and sink and thus causes the ocean mixed layer to deepen. The changes in the Pacific subtropical high are related to changes in the continental monsoon region. Since the 170Ma, the Pangea supercontinent splits up, causing the supercontinent's inland water vapor to increase, the land monsoon area to increase, and the ocean monsoon area to decrease. According to the "monsoon-desert mechanism" of Rodwell and Hoskins, we can understand the relationship between the strengthening of land monsoon condensation heating and the formation of subtropical high over the western ocean.</p>

Evapotranspiration and CO2 exchange of wet and snow-loaded canopy in an evergreen temperate coniferous forest

<p>Learning about the gas exchange dynamic (evapotranspiration and photosynthesis) relating to precipitation and leaf wetness is important for understanding the forest hydrological and carbon sink function. Precipitation can lead to the change in meteorological factors, depression on leaf gas exchange as well as increasing CO<sub>2</sub> emission from soil. However, few studies fully consider the effect of these changes in ecosystem scale.</p><p>This study conducted continuous eddy covariance measurement over a temperate evergreen Japanese cypress forest canopy in the Asian monsoon area from 2016 to 2019. By applying the eddy covariance method with the enclosed path gas analyzer, evapotranspiration and CO<sub>2</sub> exchange from the canopy to the atmosphere during and after rainfall and snow are precisely monitored. The chamber method is used to simultaneously measure the soil respiration. Especially, to reveal the mechanism of wet canopy gas exchange mechanism, a SVAT multilayer model with two rainfall interception solution (Model 1: free gas exchange with interception only by the adaxial surface; Model 2: no gas exchange with interception by both surfaces) is applied to figure out the interception distribution over the leaf surface.</p><p>The annual average daytime latent heat flux (λE) was 70.92 W m<sup>-2</sup>, 22.31 W m<sup>-2</sup>, 139.40 W m<sup>-2</sup> for wet canopy, snow-loaded canopy and the first 6 hours after wetness ended; the annual average daytime net ecosystem exchange was -1.9 μmol m<sup>-2</sup>s<sup>-1</sup>, -0.42 μmol m<sup>-2</sup>s<sup>-1</sup>, -7.43 μmol m<sup>-2</sup>s<sup>-1</sup> for wet canopy, snow-loaded canopy and the first 6 hours after wetness ended. Correspondingly, the annual average daytime soil CO<sub>2</sub> flux was 2.53 μmol m<sup>-2</sup>s<sup>-1</sup>, 0.26 μmol m<sup>-2</sup>s<sup>-1</sup>, 2.93 μmol m<sup>-2</sup>s<sup>-1</sup> when the canopy was wet, snow-loaded and during the first 6 hours after wetness ended. The gas exchange at the first 6 hours after wet is more active than that of wet canopy and snow-loaded canopy despite rainfall increased the CO<sub>2</sub> emission from the soil. Both measured data and simulation show the wet canopy can process gas exchange. The simulation showed that both interception situations are possible to happen but Model 1 is more suitable for this temperate forest. Meanwhile, the difference between the two models’ performance is smaller during the rainfall than in the wet period after the rainfall, which means interception distribution had a larger impact on wet canopy gas exchange at the later wet period. Future studies should also concern about the mechanism and effect of gas exchange dynamics relating to different precipitation patterns and water sources for latent heat flux.</p>