Greening in the circumpolar high-latitude may amplify warming in the growing season

We present a study that suggests greening in the circumpolar high-latitude regions amplifies surface warming in the growing season (May–September) under enhanced greenhouse conditions. The investigation used a series of climate simulations with the Community Atmospheric Model version 3—which incorporates a coupled, dynamic global vegetation model—with and without vegetation feedback, under both present and doubled CO₂ concentrations. Results indicate that climate warming and associated changes promote circumpolar greening with northward expansion and enhanced greenness of both the Arctic tundra and boreal forest regions. This leads to additional surface warming in the high-latitudes in the growing season, primarily through more absorption of incoming solar radiation. The resulting surface and tropospheric warming in the high-latitude and Arctic regions weakens prevailing tropospheric westerlies over 45–70N, leading to the formation of anticyclonic pressure anomalies in the Arctic regions. These pressure anomalies resemble the anomalous circulation pattern during the negative phase of winter Arctic Oscillation. It is suggested that these circulation anomalies reinforce the high-latitude and Arctic warming in the growing season.     

Evaluating observed and projected future climate changes for the Arctic using the K?ppen-Trewartha climate classification

The ecosystems in the Arctic region are known to be very sensitive to climate changes. The accelerated warming for the past several decades has profoundly influenced the lives of the native populations and ecosystems in the Arctic. Given that the K?ppen-Trewartha (K-T) climate classification is based on reliable variations of land-surface types (especially vegetation), this study used the K-T scheme to evaluate climate changes and their impact on vegetation for the Arctic (north of 50°N) by analyzing observations as well as model simulations for the period 1900–2099. The models include 16 fully coupled global climate models from the Intergovernmental Panel on Climate Change Fourth Assessment. By the end of this century, the annual-mean surface temperature averaged over Arctic land regions is projected to increase by 3.1, 4.6 and 5.3°C under the Special Report on Emissions Scenario (SRES) B1, A1b, and A2 emission scenarios, respectively. Increasing temperature favors a northward expansion of temperate climate (i.e., Dc and Do in the K-T classification) and boreal oceanic climate (i.e., Eo) types into areas previously covered by boreal continental climate (i.e., Ec) and tundra; and tundra into areas occupied by permanent ice. The tundra region is projected to shrink by ?1.86?×?10⁶?km² (?33.0%) in B1, ?2.4?×?10⁶?km² (?42.6%) in A1b, and ?2.5?×?10⁶?km² (?44.2%) in A2 scenarios by the end of this century. The Ec climate type retreats at least 5° poleward of its present location, resulting in ?18.9, ?30.2, and ?37.1% declines in areal coverage under the B1, A1b and A2 scenarios, respectively. The temperate climate types (Dc and Do) advance and take over the area previously covered by Ec. The area covered by Dc climate expands by 4.61?×?10⁶?km² (84.6%) in B1, 6.88?×?10⁶?km² (126.4%) in A1b, and 8.16?×?10⁶?km² (149.6%) in A2 scenarios. The projected redistributions of K-T climate types also differ regionally. In northern Europe and Alaska, the warming may cause more rapid expansion of temperate climate types. Overall, the climate types in 25, 39.1, and 45% of the entire Arctic region are projected to change by the end of this century under the B1, A1b, and A2 scenarios, respectively. Because the K-T climate classification was constructed on the basis of vegetation types, and each K-T climate type is closely associated with certain prevalent vegetation species, the projected large shift in climate types suggests extensive broad-scale redistribution of prevalent ecoregions in the Arctic.     

Luminous infrared galaxies with the submillimeter array: probing the extremes of star formation

Luminous and Ultraluminous infrared galaxies (ULIRGs) contain the most intense regions of star formation in the local universe. Because molecular gas is the fuel for current and future star formation, the physical properties and distribution of the warm, dense molecular gas are key components for understanding the processes and timescales controlling star formation in these merger and merger remnant galaxies. We present new results from a legacy project on the Submillimeter Array which is producing high resolution images of a representative sample of galaxies with log L _FIR >11.4 and D<200 Mpc.     

Diurnal circulations and their multi-scale interaction leading to rainfall over the South China Sea upstream of the Philippines during intraseasonal monsoon westerly wind bursts

The morning diurnal precipitation maximum over the coastal sea upstream of the Philippines during intraseasonal westerly wind bursts is examined from observations and numerical model simulations. A well-defined case of precipitation and large-scale circulation over the coastal sea west of the Philippines during 17?C27 June 2004 is selected as a representative case. The hypothesis is that the mesoscale diurnal circulation over the Philippines and a large-scale diurnal circulation that is induced by large-scale differential heating over Asian continent and the surrounding ocean interact to produce the offshore precipitation maximum during the morning. Three-hourly combined satellite microwave and infrared rainfall retrievals define the morning rainfall peak during this period, and then later the stratiform rain area extends toward the open sea. A control numerical simulation in which a grid-nudging four-dimensional data assimilation (FDDA) is applied to force the large-scale diurnal circulation represents reasonably well the morning rainfall maximum. An enhanced low-level convergence similar to observations is simulated due to the interaction of the local- and large-scale diurnal circulations. The essential role of the local-scale diurnal circulation is illustrated in a sensitivity test in which the solar zenith angle is fixed at 7?am to suppress this diurnal circulation. The implication for climate diagnosis or modeling of such upstream coastal sea precipitation maxima is that the diurnal variations of both the local- and the large-scale circulations must be taken into consideration.     

An experimental study on the rocking response of bridge piers with spread footing foundations

Some spread footing foundations from real retrofitting practices in Taiwan were extended to be uneconomically large due to the restriction of foundation uplift regulated in the design code. Although rocking mode of spread footings induced from foundation uplift is not favorable in current design code, recent studies have shown that the rocking of a spread footing may have a beneficial effect on the dynamic performance of piers by reducing the earthquake forces that can be transmitted to the pier base. This implies that the plastic deformation that occurs at the pier's plastic zone can be decreased and as a result the ductility demand of piers can possibly be reduced. In order to gain a better understanding of the structural behavior related to rocking and to clarify that if the widening and strengthening of the foundations to limit the rocking mechanism of spread footing is necessary for the retrofitting work, a series of preliminary rocking experiments were performed. A total of three circular reinforced concrete columns with spread footing foundations were tested. Using pseudo‐dynamic tests and a cyclic loading test, these columns were subjected to different levels of earthquake accelerations, including a near field ground motion. The results of the tests and the rocking behavior of the footings are discussed in this paper. From the benchmark test, the difference between the response behavior of a rocking base and a fixed base foundation was highlighted. By comparing the experimental responses of the retrofitted column with the responses of the original one, the effect of the rocking mechanism on the ductility demand and strength demand of the columns was also identified. Copyright © 2010 John Wiley & Sons, Ltd.     

Electrokinetic Restoration of Sulfate‐Accumulated Saline Greenhouse Soil

Electrokinetic (EK) process was performed to restore sulfate‐originated saline soil and to evaluate the effect of treatment duration. Sulfate and potassium were the major ionic salts in the saline soil used in this study. A constant voltage gradient of 1 V/cm was applied for 8, 12, and 16 days. After EK treatment, anions and cations were transported toward anode and cathode, respectively, by electromigration. Chloride was completely removed, and 85.6% of nitrate was removed after 8 days of treatment. The increase of treatment period from 8 to 12 days had a negligible effect on the enhancement in the rate of sulfate removal; however, over 70% was removed after16 days. At the end of experiment, the electrical conductivity (EC) of the soil, an indicator of soil salinity, decreased to 1.93 dS/m from an initial value of 5.3 dS/m, and the distribution of sulfate was similar to that of EC. The operation time of 16 days was sufficient to restore the sulfate‐originated saline soil using the EK process.     

Numerical simulation of vertical ground heat exchangers: Intermittent operation in unsaturated soil conditions

The effect of varying the thermal properties of inhomogeneous unsaturated soil on the intermittent operation of a vertical ground heat exchanger (GHE) was simulated by a conjugate heat transfer simulation using a transient conductive heat transfer model. A three-phase soil model was used to introduce soil properties that vary with depth. The performance during the first few hours was significantly different from that of an analytical infinite line source model that assumes steady-state borehole conditions, although relatively good agreement was obtained thereafter. Unsaturated soil conditions afforded a 40% lower mean heat exchange rate than saturated conditions. This demonstrates the importance of considering unsaturated conditions in the design and performance evaluation of GHEs.