Sub-kilometer Scale Research Articles

Regional Climate Change: Downscaling, Prediction, and Impact Assessment

Although the issue of climate change is often dealt with in global perspective, the impact of climate change must be assessed at regional scales. While global climate models can provide projections of the average state of large-scale circulation of future climate, the downscaling of such projections to regional scale with improved spatial and temporal resolution for both the forcing fields and the climatic responses is the basis for assessing the societal impacts of climate change. Therefore, it is important to not only study climate change at the global scale but also study the regional manifestations of the climate system at spatial scales ranging from less than a hundred kilometers to thousands of kilometers with time scales from months to years to decades. This special issue publishes a collection of articles covering a wide range of topics of our understanding of “regional climate” from downscaling the variability of extreme rainfall over the Yangtze River basin (T. Gao and L. Xie) and assessing the water resources in the Yellow River region (Z. Wu et al.) in China to forecasting the precipitation and water resources in the Lake Victoria region in East Africa (X. Sun et al., R. Argent et al., and K. A. Smith and F. H. M. Semazzi), from downscaling wind energy resources in the contiguous United States (B. Liu et al.) to characterizing the precipitation extremes in the Carpathian region in central and southern Europe (L. Gaal et al.), and from analyzing the energy balance in semiarid grasslands in China (Q. Jiang et al.) to detecting future climate change signals in central and eastern Europe from numerical model simulations (M. Belda et al.). This special issue also includes articles addressing the impacts of regional climate change on tropical cyclones over the Atlantic Ocean (K. Xie and B. Liu), on crop yields in North China (H. Liu et al.), and on litter production and nutrient dynamics in a plantation in China (X. Ge et al.), as well as rainfall and drought in Eastern Kenya (M. O. Kisaka et al.). Additionally, several articles with focus on regional climate downscaling methodologies are also included. S. Kim et al. studied the effects of geographic features in a mountainous area on the downscaling of global climate model data; T. R. Lee et al. demonstrated the feasibility of using PRISM (parameterelevation regression on independent slope model) to downscale maximum temperature to subkilometer scale; L. Gao et al. applied the LASSO algorithm to statistically downscale the ERA-interim precipitation forecast over complex terrain; and K.-H. Min and W.-Y. Sun explored the application of an atmosphere-cryosphere coupledmodel in regional climate applications. These articles reflect the recent advances and applications in “regional climate downscaling, prediction, and impact assessment” from a set of unique angles. We hope they are of interest to peers.

Translating aboveground cosmic-ray neutron intensity to high-frequency soil moisture profiles at sub-kilometer scale

Abstract. Above-ground cosmic-ray neutron measurements provide an opportunity to infer soil moisture at the sub-kilometer scale. Initial efforts to assimilate those measurements have shown promise. This study expands such analysis by investigating (1) how the information from aboveground cosmic-ray neutrons can constrain the soil moisture at distinct depths simulated by a land surface model, and (2) how changes in data availability (in terms of retrieval frequency) impact the dynamics of simulated soil moisture profiles. We employ ensemble data assimilation techniques in a "nearly-identical twin" experiment applied at semi-arid shrubland, rainfed agricultural field, and mixed forest biomes in the USA. The performance of the Noah land surface model is compared with and without assimilation of observations at hourly intervals, as well as every 2 days. Synthetic observations of aboveground cosmic-ray neutrons better constrain the soil moisture simulated by Noah in root-zone soil layers (0–100cm), despite the limited measurement depth of the sensor (estimated to be 12–20cm). The ability of Noah to reproduce a "true" soil moisture profile is remarkably good, regardless of the frequency of observations at the semi-arid site. However, soil moisture profiles are better constrained when assimilating synthetic cosmic-ray neutron observations hourly rather than every 2 days at the cropland and mixed forest sites. This indicates potential benefits for hydrometeorological modeling when soil moisture measurements are available at a relatively high frequency. Moreover, differences in summertime meteorological forcing between the semi-arid site and the other two sites may indicate a possible controlling factor to soil moisture dynamics in addition to differences in soil and vegetation properties.

Batholith tectonics: Formation and deformation of ghost stratigraphy during assembly of the mid-crustal Andalshatten batholith, central Norway

The Andalshatten batholith (322 km 2 , >700 km 3 ) is a predominantly granodioritic high-K, calc-alkaline igneous body that was assembled in the mid-crust across four lithologically distinct nappes within the Helgeland Nappe Complex, central Norway. Extensive vertical and horizontal exposures of metamorphic screens and xenoliths within the batholith provide an unparalleled view of the nature of magma emplacement, host rock displacement, and batholith assembly, i.e., batholith tectonics. The mapped intrusion consists of at least five distinct lithologic phases, including schlieren-banded to gneissic granodiorite (11% of batholith area), coarse-crystalline to K-feldspar megacrystic granodiorite (69%), amphibole-bearing diorite (11%), tonalite (2%), and minor leucogranite. Contacts between phases are both sharp and/or gradational and are interpreted to reflect comagmatic behavior over the duration of crystallization of the phases separated by a given contact. New chemical abrasion–thermal ionization mass spectrometry 206 Pb/ 238 U zircon weighted mean ages of 442.67 ± 0.14 Ma and 441.53 ± 0.40 Ma for 2 samples of the voluminous megacrystic granodiorite from disparate localities indicate distinct periods of zircon crystallization separated by ∼1 Ma; titanite ages for these samples are 441.30 ± 0.21 Ma and 436.10 ± 2.80 Ma, respectively. No observable contacts were identified between these two lithologically similar localities. Of the mapped intrusion area, ∼8% (>24 km 2 ) comprises screens (kilometer scale) and xenoliths (subkilometer scale) of metamorphic rocks that reflect the skeletal framework of the host rock nappes into which the granodioritic magmas intruded. This ghost stratigraphy maintains broad continuity with host rock lithology and structural trends. The largest screens show no evidence of internal, emplacement-related ductile deformation, but appear to be rigidly rotated into subparallelism with the western host rock contact, presumably during subsequent magma injection into the batholith. In contrast, xenoliths underwent rotation, translation, and internal deformation in the magma. The scale dependence of synmagmatic deformation of screens and xenoliths is likely the result of smaller blocks becoming thermally equilibrated with the surrounding magma and thus deforming by ductile mechanisms in a magma with increasing yield strength due to crystallization. We interpret the Andalshatten batholith to have been assembled by at least five spatially distinct, elongate batches of magma over a minimum duration 600 ka to 1.7 Ma, including significant recharge events involving dioritic magmas. Local space for batholith assembly was accommodated by brittle and ductile deformation, including viscous flow of host rocks in a dynamothermal contact aureole. Viscous flow was facilitated by reactivation of existing structures (e.g., tightening of interlimb fold angles), recrystallization, and penetrative foliation development, resulting in near-field lateral and downward-directed displacement of host rocks along the western margin during batholith expansion and growth. Emplacement of dioritic magmas added heat and mass to the growing reservoir, enabling significant magnitudes of internal, hypersolidus flow, magmatic foliation development, mechanical mingling, and screen deformation. These observations and data sets are consistent with the hypothesis of multiple recharge events in a magma chamber that was partially molten over reasonably large spatial scales, thereby allowing screens and xenoliths to be incorporated and displaced and/or deformed.

Very Dense Seismic Array Observations in Furukawa District, Japan

On 11 March 2011, the Tohoku earthquake ( M w 9.0) hit the eastern part of Japan’s mainland off the Pacific coast, and killed more than 10,000 people, due mainly to a great tsunami in the immediate onshore region. Strong ground motions during the earthquake were observed in almost the whole region of Japan by K‐NET, KiK‐net organized by National Research Institute for Earth Science and Disaster Prevention (NIED), and the other seismometer networks. At least 17 of the K‐NET and KiK‐net stations observed over 980 cm/s2 of peak ground acceleration (PGA) in horizontal components, and two stations observed over 6.5 of high seismic intensity on the Japan Meteorological Agency (JMA) scale. However, damage in areas due to ground motion do not correspond to either the large PGA or the high seismic intensity (e.g., Motosaka, 2012; Goto and Morikawa, 2012, forthcoming). We focus on the Furukawa district of Osaki City, where severe residential damage occurred downtown. Ground‐motion records in the downtown area are available from two stations, MYG006 (K‐NET) and JMA Furukawa (JMA). The damage level was different between the areas within several hundred meters from the MYG006 and JMA Furukawa stations, which are separated by about 1 km. The severe damages were concentrated within an area approximately 1×1 km2 including the JMA station. This implies that the ground‐motion characteristics were not uniform in subkilometer scale, and the existing two stations are not enough to clarify the damage distribution. In the aftermath of the earthquake, we distributed dozens of low‐cost seismometers, namely the ITK sensor, around an area about 3×2 km2 in the Furukawa district. The observed data were sent to the remote server through an Internet connection in real time. The seismometers were installed beside the volunteers’ houses. The volunteers can access the interactive information service, namely the online viewer …

Forecasting Cloud Cover and Atmospheric Seeing for Astronomical Observing: Application and Evaluation of the Global Forecast System

ABSTRACTTo explore the issue of performing a noninteractive numerical weather forecast with an operational global model to assist with astronomical observing, we use the Xu-Randall cloud scheme and the Trinquet-Vernin AXP seeing model with the global numerical output from the Global Forecast System (GFS) to generate 3–72 hr forecasts for cloud coverage and atmospheric seeing, and we compare them with sequence observations from nine sites from different regions of the world with different climatic backgrounds in the period from 2008 January to 2009 December. The evaluation shows that the proportion of prefect forecast of cloud cover forecast varies from ∼50% to ∼85%. The probability of cloud detection is estimated to be around ∼30% to ∼90%, while the false alarm rate is generally moderate and is much lower than the probability of detection in most cases. The seeing forecast has a moderate mean difference (absolute mean difference < 0.3″ in most cases) and rms error (0.2″–0.4″ in most cases), compared with the observation. The probability of forecast with < 30% error varies between 40% and 50% for the entire-atmosphere forecast and between 30% and 50% for the free-atmosphere forecast for almost all sites, which is in the better cluster among major seeing models. However, the forecast errors are quite large for a few particular sites. Further analysis suggests that the error might primarily be caused by the poor capability of the GFS/AXP model to simulate the effect of turbulence near ground and on a subkilometer scale. Overall, although the quality of the GFS model forecast may not be comparable with the human-participated forecast at this moment, our study has illustrated its suitability for a basic observing reference and has proposed its potential to gain better performance with additional efforts on model refinement.

Net community production and gross primary production rates in the western equatorial Pacific

Net community production (NCP) and gross primary production (GPP) are two key metrics for quantifying the biological carbon cycle. In this study, we present a detailed characterization of NCP and GPP in the western equatorial Pacific during August and September 2006. We use continuous measurements of dissolved gases (O2 and Ar) in the surface water in order to quantify NCP at subkilometer scale resolution. We constrain GPP in discrete samples using the triple isotopic composition of O2. We find the average NCP in the western equatorial Pacific is 5.9 ± 0.9 mmol O2 m−2 d−1 (equivalent to 1.5 ± 0.2 mol C m−2 yr−1 with error estimates reflecting 1σ confidence levels) and the average GPP is 121 ± 34 mmol O2 m−2 d−1 (equivalent to 32 ± 9 mol C m−2 yr−1). The measurements reveal significant spatial variability on length scales as small as 50 km. The NCP/GPP ratio is 5.7% ± 1.8%. We also present results for NCP and GPP in the coastal area off Papua New Guinea and for GPP in the central Pacific along the equator.

Kilometer‐scale roughness of Mars: Results from MOLA data analysis

The Mars Orbiter Laser Altimeter (MOLA) data are used to characterize the kilometer‐scale surface roughness of Mars. The median absolute value of the differential slope at a given baseline is proposed as a data‐derived measure of the surface roughness at this scale. Study of the scale dependence of roughness for the smoothest terrains gives an independent estimate of 20 cm for MOLA ranging accuracy. The baseline lengths from 0.6 to ∼20 km are used, and kilometer‐scale roughness is mapped for the entire surface. The maps show that different geological units have distinctive roughness characteristics. Scale dependence of roughness for a number of geological units is presented and discussed. The southern polar cap is rougher than the northern at kilometer and subkilometer scale, which suggests differences in the sublimation/condensation balance. The Vastitas Borealis Formation has a distinctive 3‐km‐scale background surface topography, which suggests a nonvolcanic origin for its upper layer. Young volcanic plains in Amazonis Planitia and the eastern part of Elysium Planitia are very similar to each other in their roughness characteristics and differ from other volcanic plains on Mars, which suggests a distinctive eruption style. There are systematic latitudinal variations of roughness in both the southern highlands and the northern lowlands: terrains at high latitude are smoother at short baselines; the characteristic vertical scale related to this difference is several meters. Processes that could be responsible for formation of this trend include creep of ice‐rich near‐surface material at high latitudes, treatment of the surface with repetitive deposition and sublimation of seasonal frost, climate‐controlled deposition and/or cementation of dust at high latitudes, and repetitive sublimation and accumulation of subsurface ice at low latitudes with climate variations. All mechanisms of origin could operate more effectively under different climate conditions. Relevant morphological observations favor mechanisms involving deposition of smooth blankets at high latitudes.

Experimental study of the collisional parallel velocity shear instability

Simultaneous density and electric field fluctuation spectra, associated with velocity shear (both in the transverse to the magnetic field ion flow velocity and in the parallel ion flow velocity), have been observed by the DE 2 spacecraft in the F region [Basu et al., 1984]. Basu and Coppi [1988, 1989] argued that the subkilometer scale irregularities are due to collisional electrostatic modes excited in a partially ionized plasma in the presence of shear in the parallel ion flow. In this paper we describe results of a laboratory investigation of the effects of neutral‐particle collisions on the parallel velocity shear instability, performed using a double‐ended Q machine. The critical value of the shear dv0/dx, the derivative of the field‐aligned ion flow with respect to the transverse (to B) coordinate, is determined and compared with theoretical predictions.

Evolution of subkilometer scale ionospheric irregularities generated by high‐power HF waves

Electron density irregularities in the F region excited by the European incoherent scatter (EISCAT) high‐power high‐frequency (HF) facility in Ramfjordmoen, Norway, have been studied in detail by observing scintillations of 250‐MHz satellite signals traversing the HF beam. Spaced antenna measurements were performed to determine the temporal structure of scintillation and the drift of the irregularities. Studies of scintillation spectra indicate that even though the onset occurs nearly simultaneously for all irregularity scale sizes, the electron density irregularities with wavelengths in the range of 50–15 m attain their saturation amplitudes within tens of seconds, whereas longer scale‐size irregularities with wavelengths exceeding 100 m saturate in the timescale of minutes. The threshold power density requirement for the generation of irregularities of different scales has also been studied by the variation of the heater power. It is found that for large‐scale (&gt;100 m) irregularities the threshold power density varies inversely as the irregularity wavelength with a power law index of 4 as predicted by the theories of self‐focusing instability.

Clustering, randomness, and regularity in cloud fields: 3. The nature and distribution of clusters

This study applies the K‐nearest‐neighbor (KNN) statistic as well as a morphological filtering approach for the identification and analysis of cloud clusters. These approaches first are evaluated by application to synthetically generated normally distributed clusters within a random background. They are found to provide conservative estimates of cluster size while accurately estimating the percentage of clouds in clusters. In Landsat scenes, typical clusters are found to contain four to five clouds and typically two to three clouds per cluster in advanced very high resolution radiometer (AVHRR) data. In the Landsat imagery the KNN analysis finds that about 15% to 50% of the total cloud field participates in clusters. These clusters are found to be concentrated in less than 2% of the total cloud field area. In AVHRR scenes the KNN method yields from 1.5% to 16% of the cloud field participating in clusters, concentrated within 1% of the total cloud field area. Mean cluster radii are typically 300 m to 600 m in the Landsat scenes and less than 3 km in the AVHRR images. Both the cloud cluster centers and the non‐participating background clouds are randomly distributed within the cloud field. Less than 10% of the cloud clusters form superclusters (i.e., clusters of clusters). When clouds are segregated into classes of uniform size, the clustering signal weakens with increasing cloud size. When the scene as a whole is divided into 30‐km subregions, the clustering signal is relatively homogeneous throughout the scene in spite of significant fluctuations in cloud number density within the various subregions. These results show that the physical mechanism underlying this clustering signal, although producing clusters on scales less than 3 km, is operative over the entire field. A nearest‐neighbor angle statistic is applied to search for regularity at the subkilometer scale. The angle statistic results are consistent with normally distributed point processes and inconsistent with any form of regularity at this scale. Presently, no method is presented which is effective at probing the cloud field structure at scales intermediate to 2 km and 30 km. Therefore cloud field regularity cannot be ruled out at these intermediate scales.

Copernicus: A Regional Probe of the Lunar Interior

Earth-based telescopic spectral imaging techniques were used to document the spatial distribution of crater materials within the large lunar crater Copernicus at the subkilometer scale on the basis of spectral ultraviolet-visible-near-infrared characteristics. The proposed spectral mixing analysis leads to a first-order mapping of the impact melt material within the crater. Olivine was detected not only within the three central peaks but also along a significant portion of the crater rim. Consideration of an olivine-bearing end-member in the mixing model emphasizes the overall morphological pattern of the rim and wall terraces in the associated fraction image. The identification of widely exposed olivine units supports the idea that the lower crust and possibly the lunar mantle itself are regionally at shallow depth.

Velocity shear and fluctuations in the auroral regions of the ionosphere

The theory of collisional electrostatic modes that are driven unstable by a sheared field‐aligned ion flow velocity (i.e., Vi0 = V0(x)ez, B0 = B0ez) is presented. The instability threshold condition is |dV0/dx| &gt; 2(1 + Ti/Te)νin, where νin is the ion‐neutral collision frequency, the characteristic longitudinal wavelengths λ∥ &gt; λe, λe being the electron collision mean free path, and the transverse wavelengths λ⊥ &gt; 21/2πρi, ρi being the ion gyroradius. The linearly unstable modes can account for fluctuations with transverse wavelengths ranging from a kilometer to several meters for only a moderate amount of shear (in the parallel velocity). Thus the instability provides a direct means of exciting almost the entire range of the observed (Basu et al., 1988) subkilometer scale irregularities in the auroral F region. The quasi‐linear analysis presented here shows that an effective viscosity describing momentum transport in the x direction can be derived in the presence of the shear‐driven fluctuations. The spatial profiles of the excited modes are evaluated from the solution of the appropriate dispersion equation. A model is proposed to describe the nonlinear evolution of the instability while ensuring that the characteristics of the turbulent fluctuation spectra resulting from it are consistent with those of the observed spectra.