News Update on Earth’s Surface: May 21

[1] Changes in ultraviolet-radiation reaching the earths surface

The quality and quantity of UV measurements have increased greatly in the last few years. Variations among measurements from different instruments are diminishing toward the 5% level. Long-term trend detection is still a problem, with little historical data available for baseline estimations. Enhanced UV levels are clearly associated with the Antarctic springtime ozone reductions. Measurements show that maximum UV levels at the South Pole are reached well before the summer solstice, and DNA-damaging radiation at Palmer Station, Antarctica (64 degrees S) during the springtime ozone depletion can exceed maximum summer values at San Diego, USA (32 degrees N). UV increases at mid-latitudes are smaller. However, increases associated with the record low ozone column of 1992/93 in the Northern Hemisphere are evident when examined on a wavelength-specific basis. Measurements in Argentina, Chile, New Zealand, and Australia show relatively high UV levels compared to corresponding Northern Hemispheric latitudes, with differences in both stratospheric ozone and tropospheric pollutants likely to be playing a role. Tropospheric ozone and aerosols can reduce global UV-B irradiances appreciably. At some locations, tropospheric pollution has increased since pre-industrial times, leading to decreases in surface UV radiation. However, recent trends in tropospheric pollution probably had only minor effects on UV trends relative to the effect of stratospheric ozone reductions. Global ozone measurements from satellites over the period 1979-1993 imply significant UV-B increases at high and mid-latitudes of both hemispheres, but only small changes in the tropics. Such estimates however assume that cloud cover and tropospheric pollution have remained constant over this time period. Under the current CFC phase-out schedules, global UV levels are predicted to peak around the turn of the century in association with peak loading of chlorine in the stratosphere and the concomitant ozone reductions. The recovery to pre-ozone depletion levels is expected to take place gradually over the next 50 years.

[2] Monitoring Earth Surface Dynamics With Optical Imagery

The increasing availability of high‐quality optical satellite images should allow, in principle, continuous monitoring of Earth’s surface changes due to geologic processes, climate change, or anthropic activity. For instance, sequential optical images have been used to measure displacements at Earth’s surface due to coseismic ground deformation [e.g., Van Puymbroeck et al., 2000], ice flow [Scambos et al., 1992; Berthier et al., 2005], sand dune migration [Crippen, 1992], and landslides [Kääb, 2002; Delacourt et al., 2004].

Surface changes related to agriculture, deforestation, urbanization, and erosion—which do not involve ground displacement—might also be monitored, provided that the images can be registered with sufficient accuracy. Although the approach is simple in principle, its use is still limited, mainly because of geometric distortion of the images induced by the imaging system, biased correlation techniques, and implementation difficulties.


[3] Geological consequences of super‐sized Earths

The discovery of terrestrial‐scale extrasolar planets, and their calculated abundance in the galaxy, has prompted speculation on their surface conditions and thermal structure. Both are dependent on the tectonic regime of a planet, which is itself a function of the balance between driving forces, and the resistive strength of the lithosphere. Here we use mantle convection simulations to show that simply increasing planetary radius acts to decrease the ratio of driving to resisting stresses, and thus super‐sized Earths are likely to be in an episodic or stagnant lid regime. This effect is robust when associated increases in gravity are included, as the more dominant effect is increased fault strength rather than greater buoyancy forces. The thermo‐tectonic evolution of large terrestrial planets is more complex than often assumed, and this has implications for the surface and conditions habitability of such worlds.

[4] Effective Earth Radius Factor Prediction and Mapping for Ondo State, South Western Nigeria

Accurate prediction and determination of the effective earth radius factor (k-factor) is critical for optimal performance in the design and planning of terrestrial line of sight communication links. In this work an artificial neural network (ANN) model is developed and used to predict k-factor values for four towns in Ondo State using satellite derived data. The towns are Okitipupa (6.5ºN, 4.78ºE), Ondo (7.11ºN, 4.83ºE), Akure (7.25ºN, 5.2ºE) and Ikare (7.52ºN, 5.75ºE). A feed forward back propagation ANN was implemented, thereafter trained, validated and tested using satellite derived data for the period from 1984 to 2002. Mean absolute error (MAE) was used to evaluate the performance of the ANN. The MAE values obtained were 0.0024, 0.0014, 0.002 and 0.003 for Okitipupa, Akure, Ikare and Ondo towns respectively. Contour map showing the predicted k-factor values interpolated over the map of Ondo state was plotted using Geographical Information System (GIS) techniques. The study concluded that ANN presents an effective means of predicting the average k-factor values over a geographical location.

[5] A Review on Effects and Control of Seepage through Earth-fill Dam


All earthfill dams have seepage from water percolating slowly through the dam and its foundation. Many seepage problems and failure of earth-fill dams have occurred because of inadequate seepage control measures. This study was reviewed the conditions, causes, and effects of seepage and control measures in the earth dam. Types of earth dams such as homogeneous embankment, zoned embankment and diaphragm embankment well were highlighted.  Seepage conditions, such as rapid water level decreases or the water falling below the level expected with normal use (sudden drawdown condition), wet spots and aquatic vegetation (like cattails) below the dam; causes, such as poor compaction of environment soil, poor foundation and abutment preparation, Rodent holes, Rooted tree roots and wood and so no and effects due to piping, internal erosion, solutioning, internal pressure and saturation and uplift, heave and blowout were highlighted. This study also examines the control measures included cut-offs; upstream clay blanket; filter blanket; seepage drains; berms and loading berm; upstream and downstream slope protections; And relief well. Besides, in order to keep continuous watch on the health of dam and monitor that is, take curative steps before failure occurs., instruments such as pore pressure, settlement gauges, horizontal movement devices, and seismic activity measurements should be embedded into the dam were mentioned.




[1] Madronich, S., McKenzie, R.L., Caldwell, M. and Björn, L.O., 1995. Changes in ultraviolet-radiation reaching the earths surface. Ambio24(3), pp.143-152.

[2] Leprince, S., Berthier, E., Ayoub, F., Delacourt, C. and Avouac, J.P., 2008. Monitoring earth surface dynamics with optical imagery. Eos, Transactions American Geophysical Union89(1), pp.1-2.

[3] O’neill, C. and Lenardic, A., 2007. Geological consequences of super‐sized Earths. Geophysical Research Letters34(19).

[4] Atijosan, A.O., Badru, R.A., Muibi, K.H., Ogunyemi, S.A. and Alaga, A.T., 2015. Effective Earth Radius Factor Prediction and Mapping for Ondo State, South Western Nigeria. Journal of Scientific Research and Reports, pp.540-548.

[5] Omofunmi, O.E., Kolo, J.G., Oladipo, A.S., Diabana, P.D. and Ojo, A.S., 2017. A review on effects and control of seepage through earth-fill dam. Current Journal of Applied Science and Technology, pp.1-11.

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