A spatial temporal downscaling approach to development of IDF relations for Perth airport region in the context of climate change

ABSTRACT

Downscaling of climate projections is the most adapted method to assess the impacts of climate change at regional and local scales. This study utilized both spatial and temporal downscaling approaches to develop intensity–duration–frequency (IDF) relations for sub-daily rainfall extremes in the Perth airport area. A multiple regression-based statistical downscaling model tool was used for spatial downscaling of daily rainfall using general circulation models (GCMs) (Hadley Centre’s GCM and Canadian Global Climate Model) climate variables. A simple scaling regime was identified for 30 minutes to 24 hours duration of observed annual maximum (AM) rainfall. Then, statistical properties of sub-daily AM rainfall were estimated by scaling an invariant model based on the generalized extreme value distribution. RMSE, Nash-Sutcliffe efficiency coefficient and percentage bias values were estimated to check the accuracy of downscaled sub-daily rainfall. This proved the capability of the proposed approach in developing a linkage between large-scale GCM daily variables and extreme sub-daily rainfall events at a given location. Finally IDF curves were developed for future periods, which show similar extreme rainfall decreasing trends for the 2020s, 2050s and 2080s for both GCMs.

Editor M.C. Acreman; Associate editor S. Kanae     

临近空间大气扰动变化特性的定量研究

本文利用TIMED/SABER 2002年1月至2013年1月共11年的卫星温度探测数据,通过全球网格化及在网格内作数学统计的方法,得到了20~100km高度上全球网格点上温度的平均值和标准差,实现了对临近空间全球大气扰动进行定量刻画的目的.通过定量分析温度标准差的分布特性,文中得到了临近空间大气扰动的全球分布规律,并讨论了与这些分布规律相关的物理过程.结果表明,在20~70km高度上,温度标准差为1~10K,有显著的冬季/夏季的差异,冬季的温度标准差比夏季大;大气重力波扰动是最主要来源,同时大气传播性行星波引起的扰动也是来源之一.在70~100km高度上,温度标准差常年较强,量值为10~30K,冬季/夏季的差异小,低纬地区的温度标准差高于中高纬度地区,呈现许多局地化的小结构.大气重力波是引起该区域大气总扰动量的主要扰动来源,大气潮汐波、传播性行星波(准2天、准6.5天)也有重要贡献.     

Planetary waves observed by TIMED/SABER in coupling the stratosphere–mesosphere–lower thermosphere during the winter of 2003/2004: Part 2—Altitude and latitude planetary wave structure

Part 2 of the present paper is focused on the planetary wave coupling from the stratosphere to the lower thermosphere (30–120 km) during the Arctic winter of 2003/2004. The planetary waves seen in the TIMED/SABER temperature data in the latitudinal range 50°N–50°S are studied in detail. The altitude and latitude structures of the planetary wave (stationary and travelling) clearly indicate that the stratosphere and mesosphere (30–90 km) are coupled by direct vertical propagation of the planetary waves, while the lower thermosphere (above 90–95 km altitude) is only partly connected with the lower levels probably indirectly through in-situ generation of disturbances by the dissipation and breaking of gravity waves filtered by lower atmospheric planetary waves. A peculiar feature of the thermal regime in the lower thermosphere is that it is dominated by zonally symmetric planetary waves.     

Observational evidence of deep convection over Indonesian sector in relation with major stratospheric warming events of 2003–04 and 2005–06

The major sudden stratospheric warming (SSW) events of 2003–04 and 2005–06 are considered to investigate changes in equatorial convection due to circulation changes associated with the SSW events. It is observed that the SSW events are accompanied by a considerable decrease in Outgoing Longwave Radiation (OLR), a proxy for tropical convection, over equatorial latitudes (15°N–15°S) in the Indonesian sector (90°E–150°E). However, unlike noted by earlier observations, the zonal mean OLR does not show any notable relationship with the SSW events. It can be explained from the latitude–longitude map of potential vorticity (PV) at 100 hPa, which shows a tongue of high PV emanating from high latitudes towards equator and converges in the longitude band of 90°E–150°E on the day of peak warming at 1 hPa in the case of 2003–04 and 10 hPa in the case of 2005–06. The latitude-height map of Eliassen–Palm (EP) vector and its divergence show convergence of EP flux in the upper troposphere at latitudes even lower than 20°N on these days. Further, vertical winds computed from the convergence of momentum flux are upward indicating convective activity at low-latitudes and downward at mid-latitudes.     

Observations of peculiar sporadic sodium structures and their relation with wind variations

Resonance lidar observations of sodium density in the upper mesosphere region over Gadanki (13.5°N, 79.2°E) rarely show complex structures with rapid enhancements of sodium density, completely different from normal sporadic sodium structures. The hourly averaged meteor radar zonal winds over Trivandrum (8.5°N, 76.5°E) show an eastward shear with altitude during the nights, when these events are formed. As suggested by Kane et al. [2001. Joint observations of sodium enhancements and field-aligned ionospheric irregularities. Geophysical Research Letters 28, 1375–1378], our observations show that the complex structures may be formed due to Kelvin–Helmholtz instability, which can occur in the region of strong wind shear.     

The altitude dependence of magnetic remanence in the slowly-cooled Precambrian plutonic terrain of West Greenland

To evaluate the change in magnetic remanence with altitude through a slowly-cooled Precambrian basement terrain three vertical sections have been sampled in West Greenland. The study employs the principle that higher structural levels passed through their blocking temperatures earlier than lower levels and therefore record earlier pole positions, and it utilises dolerites and diorites intruded late in, or after, the tectonic history to minimise anisotropy effects. In the amphibolite facies terrain at Qa´qatoqaq (1400 m) highly-stable magnetite-held remanences move on demagnetisation progressively along small circles interpreted to record younger to older apparent polar wander (a.p.w.) motions during cooling through the blocking temperature ranges. Although the raw data show no systematic variation with altitude, when account is taken of the blocking temperature spectra as defined by thermal demagnetisation there is a systematic change in palaeofield direction in the same sense as that recorded by the demagnetisation trends. Granulite facies terrain at Igdlu´nguit qula?t (600 m) again shows systematic variation with altitude when the sites are divided into those with a remanence dominated by hemo-ilmenite and those dominated by magnetite. A third section at Praestefjeldet (250 m) yields a palaeofield reversal and a high blocking temperature component.The age evidence is evaluated to suggest that the a.p.w. path defined by 5 mean palaeopoles between 318°E, 1°N and 247°E, 38°N represents up to 50 Ma of palaeofield motion recorded by the uplift and cooling of this basement terrain at crustal depths of the order of 10 km. The calculated rate of a.p.w. motion is 1–2°/Ma and the rate of crustal uplift 10–20 m/Ma, these rates are respectively up to an order higher, and at least an order lower, than Phanerozoic rates. The collective data from Greenland agree closely with post-“Hudsonian” poles from the Laurentian Shield and represent part of a very widespread uplift event following this mobile episode. They show that altitude sections can yield a systematic record of the magnitude and direction of Precambrian a.p.w. motions provided that the blocking temperature spectra are taken into account.     

Simulating sub-daily hydrological process with SWAT: a review

ABSTRACT

The Soil and Water Assessment Tool (SWAT) is a watershed-scale hydrologic model that integrates water quantity and quality modules. Despite the large amount of knowledge on the SWAT model, specific understanding of sub-daily applications remains limited. In this review, we identify the shortcomings and possible ways forward in simulating sub-daily processes with the model. A literature review was conducted, along with a participatory method based on a questionnaire. We reviewed 28 scientific articles and categorized them into: (i) model development, (ii) streamflow methods comparison, (iii) water quality, and (iv) other applications. We found that using sub-daily data improves hydrograph peak simulation, while for medium flows use of daily data was better. From all the reviewed studies, a 1-hour time step was the most suitable time scale for the sub-daily model application. The participatory questionnaire confirmed the hypothesis that the main challenge for using the sub-daily routine was the lack of high-resolution data.     

Multi-decadal variations in annual maximum peak flows in semi-arid and temperate regions of Chile

Abstract

In determining the possible influence of climate change, it is important to understand the temporal and spatial variability in streamflow response for diverse climate zones. Thus, the aim of this study was to determine the presence of changes in annual maximum peak flow for two climate zones in Chile over the past few decades. A general analysis, a flood frequency analysis and a trend analysis were used to study such changes between 1975 and 2008 for a semi-arid (29°S–32°S) and a temperate (36°S–38°S) climatic zone. The historic annual maxima, minima and mean flows, as well as decadal mean peak flow, were compared over the period of record. The Gumbel distribution was selected to compare the 30-year flood values of two ±15-year intervals, which showed that streamflow decreased by an average of 19.5% in the semi-arid stations and increased by an average of 22.6% in the temperate stations. The Mann-Kendall test was used to investigate the temporal changes in streamflows, with negative trends being observed in 87% of the stations analysed in the semi-arid zone, and positive trends in 57% of those analysed in the temperate zone. These differences in streamflow response between climate zones could be related to recent documented increases in altitude of the zero-degree isotherm in the Andes Mountains of Chile, since most of the significant positive and negative changes were detected in first-order rivers located closer to this mountain range.

Editor D. Koutsoyiannis; Associate editor H. Lins

Citation Pizarro, R., Vera, M., Valdés, R., Helwig, B., and Olivares, C., 2013. Multi-decadal variations in annual maximum peak flows in semi-arid and temperate regions of Chile. Hydrological Sciences Journal, 59 (2), 300–311.     

Latitudinal dependence of the seasonal variation of particulate extinction in the UTLS over the Indian longitude sector during volcanically quiescent period based on lidar and SAGE-II observations

The altitude profiles of particulate extinction in the upper troposphere and lower stratosphere (UTLS) obtained from SAGE-II in the latitude region 0–30°N over the Indian longitude sector (70–90°E) are used to study the latitudinal variation of its annual pattern in this region during the volcanically quiescent period of 1998–2003. The SAGE-II data is compared with the lidar measurements from Gadanki (13.5°N, 79.2°E) when the satellite had an overhead occultation pass over a small geographical grid centered at this location. The particulate optical depth (τ_p) in the UT region shows a general decrease with increase in latitude and a pronounced summer–winter contrast with relatively low values during winter and high values during summer. In general, these variations are in accordance with the latitudinal variation of convective available potential energy (CAPE) and thunderstorm activity, which are good representative indices of tropospheric convection. While the particulate extinction (and τ_p) in the 18–21 km (LS₁) region is relatively low in the equatorial region up to 15°N, it shows an increase in the off-equatorial region, beyond 15°N. While the annual variation of τ_p in the LS₁ region is almost insignificant near the equator, it is rather well pronounced in latitude region between 10 and 15°N with relatively high values during winter and low values during summer. Beyond 20°N, this shows a prominent peak during summer. At a higher altitude, the 21–30 km (LS₂) region, the latitude variation of τ_p shows a different pattern with high values near the equator and low values in the off-equatorial region confirming the existence of a stratospheric aerosol reservoir. Low values of τ_p at lower regime (LS₁) near the equator could be due to rapid transport of particulates from the near equatorial region to higher latitudes, while the equatorial high at upper regime (LS₂) could be due to lofting and subsequent accumulation.     

Planetary waves observed by TIMED/SABER in coupling the stratosphere–mesosphere–lower thermosphere during the winter of 2003/2004: Part 1—Comparison with the UKMO temperature results

Part 1 of the present paper is focused on the types of planetary wave seen in the TIMED/SABER and UK Met Office (UKMO) temperature data in the Northern Hemisphere (NH) (0–50°N) stratosphere (30–60 km) during the Arctic winter of 2003/2004, as the emphasis is on their spatial structure (latitude and altitude) and temporal evolution particularly in relation to the stratospheric warmings. A new method for analysis of satellite data is presented in this study where the migrating and nonmigrating tides and planetary waves (stationary, zonally symmetric and travelling) are simultaneously extracted from the satellite data. The comparison between the altitude and latitude structure of the SABER and UKMO planetary waves in the temperature field of the NH stratosphere indicates a high degree of qualitative and quantitative resemblance and in this way the validity of the new data analysis method is verified as well.     

Common-volume measurements of mesospheric winds using radar and optical instruments: 1. Comparison of observations

The Millstone Hill incoherent scatter radar (42.6°N, 71.5°W) and the nearby Durham meteor wind radar (43.1°N, 70.9°W) have been used to study the structure of the winds in the mesosphere and lower thermosphere and to investigate the propagation of tidal components from the mesosphere into the lower thermosphere. In general, good agreement is found between the tidal wind amplitudes and phases determined by the two radars, but occasionally, some discontinuities have been observed in the vertical structure of the tidal components in the 90–110 km region. In order to validate the accuracy of the two techniques and the methodologies used in determining neutral winds, two common-volume experiments were conducted in 1996 and 1997 in which the two radar beams were overlayed at an altitude of 100 km. The horizontal components of the measured radar line-of-sight velocities during day-time periods were then compared at the overlapping altitudes of 95–100 km. Night-time measurements were also made using a Fabry–Perot Interferometer co-located with the radar at Millstone Hill which observed the Doppler shift of the atomic oxygen green line emission in the mesosphere. Good overall agreement is found between the instruments within the statistical uncertainties of the measurement techniques, although some differences have been found that are explained by consideration of the data statistics, the exact overlap of common volume within the different beam sizes, and the presence of altitude gradients and small scale irregularities in the sampled volumes of the atmosphere.     

Comparative influence of land and sea surfaces on the Sahelian drought: a numerical study

The aim of this work is to compare the relative impact of land and sea surface anomalies on Sahel rainfall and to describe the associated anomalies in the atmospheric general circulation. This sensitivity study was done with the Météo-France climate model: ARPEGE. The sensitivity to land surface conditions consists of changes in the management of water and heat exchanges by vegetation cover and bare soil. The sensitivity to ocean surfaces consists in forcing the lower boundary of the model with worldwide composite sea surface temperature (SST) anomalies obtained from the difference between 4 dry Sahel years and 4 wet Sahel years observed since 1970. For each case, the spatiotemporal variability of the simulated rainfall anomaly and changes in the modelled tropical easterly jet (TEJ) and African easterly jet (AEJ) are discussed. The global changes in land surface evaporation have caused a rainfall deficit over the Sahel and over the Guinea Coast. No significant changes in the simulated TEJ and an enhancement of the AEJ are found; at the surface, the energy budget and the hydrological cycle are substantially modified. On the other hand, SST anomalies induce a negative rainfall anomaly over the Sahel and a positive rainfall anomaly to the south of this area. The rainfall deficit due to those anomalies is consistent with previous diagnostic and sensitivity studies. The TEJ is weaker and the AEJ is stronger than in the reference. The composite impact of SST and land surfaces anomalies is also analyzed: the simulated rainfall anomaly is similar to the observed mean African drought patterns. This work suggests that large-scale variations of surface conditions may have a substantial influence on Sahel rainfall and shows the importance of land surface parameterization in climate change modelling. In addition, it points out the interest in accurately considering the land and sea surfaces conditions in sensitivity studies on Sahel rainfall.     

Water vapour mixing ratio profiles over Hornsund, Arctic. Intercomparison of lidar and AIRS results

Since October 2009, a ground-based Raman lidar system has been deployed to perform a regular, night-time, vertical sounding of a water vapour content in the lower and middle troposphere above Polish Polar Station at Hornsund (77.00°N, 15.55°E, 10 m a.s.l.) in the Arctic. The water vapour mixing ratio profiles were obtained for the atmosphere up to 6 km altitude, based on analysis of inelastic Raman backscattering signals from nitrogen molecules (at 387 nm) and water vapour particles (at 407 nm), calibrated with the data from a local Vaisala’s automatic meteorological station. The results obtained for winter seasons in the years 2009–2012 are in a good general agreement with the results obtained from the atmospheric infrared sounder (AIRS) on the Aqua satellite.     

Solar eclipse of the 29 March 2006: Results of the optical measurements by MORTI over Almaty (43.03°N, 76.58°E)

The observations of the upper mesosphere region (∼95 km altitude) in the period of 27–30 March 2006 using mesopause oxygen rotational temperature imager (MORTI) at Almaty (43.03°N, 76.58°E) are presented in this report to illustrate the mesosphere response to the solar eclipse (SE) event, which occurred on 29 March 2006. The nighttime volume emission rates and rotational temperatures, obtained from MORTI measurements, show appreciable differences in the pattern of wave-like oscillations observed during the period of interest. These oscillations are possibly due to the SE. Using a periodogram method the spectra of the observed wave-like oscillations, observed in the mesosphere, are examined. A physical mechanism is proposed to interpret the effects observed in terms of the mesosphere response to the total SE.     

Developing hourly intensity duration frequency curves for urban areas in India using multivariate empirical mode decomposition and scaling theory

Stochastic Environmental Research and Risk Assessment - Development of rainfall intensity–duration–frequency (IDF) curves of short duration such as hourly or sub-daily are quite...     

Dynamics of the midlatitude ionospheric <Emphasis Type="Italic">F</Emphasis> region at sunrise

The behavior of the F2 layer at sunrise has been studied based on vertical-incidence ionospheric sounding data in Almaty (76°55′E, 43°15′N). Records with small amplitudes of electron density background fluctuations were selected in order to exactly estimate the onsets of a pronounced increase in the electron density at different altitudes. It has been indicated that the electron density growth rate is a function of altitude; in this case, the growth rate at the F2 layer maximum is much lower than such values at fixed altitudes of ～30–55 km below the layer maximum. The solar zenith angle (χ) and the blanketing layer thickness (h ₀) at the beginning of a pronounced increase in the electron density at altitude h are linearly related to the h value, and these quantities vary within ～90° < χ < 100° and 180 km < h ₀ < 260 km, respectively.     

Transverse resonance in the high-latitude section of the Earth–ionosphere waveguide during the solar eclipse of March 20, 2015

The spectra of radio atmospheric signals (spherics) recorded simultaneously at two observatories of the Polar Geophysical Institute, Lovozero (67.97° N, 35.08° E) and Barentsburg (78.08° N, 14.22° E), during the solar eclipse on March 20, 2015 are presented. The peculiarities of the behavior of the first critical frequency of the Earth-ionosphere waveguide during the eclipse are described. The effective altitude of the reflective layer of ionosphere is assessed.     

Detection of solar activity signatures in OH* temperature fluctuations possibly related to the differential rotation of the Sun

Measurements of the hydroxyl rotational temperatures at about 87 km altitude above Wuppertal (51.3°N, 7.2°E), Germany, are analysed. The time series covers the time interval from 1987 until 2005 and consists of more than 4000 night mean temperature data. Seasonal and longer-term trends are removed from the data set and OH* temperature fluctuations on temporal scales of about 3–40 days are derived. Various spectral analysis techniques (harmonic analysis, maximum entropy method and wavelet transform) are applied. Can – due to the Sun's rotation – the irregular pattern of sunspots on the solar disc lead to OH* temperature fluctuations? Pronounced spectral components in the OH* temperature fluctuations around a period from 27 to 31 days are frequently observed. We tentatively attribute these signatures to the differential rotation of the Sun: Sun's equatorial regions rotate faster (taking only about 27 days) than the polar regions. Sunspots occur at heliographic latitudes at about ±40°, which correspond to a rotation rate of about 27–31 days. The OH* temperature fluctuations within this period range show a long-term modulation of 11 years. Thus, tracking the spectral intensity of the 27- to 31-day component should allow the indirect monitoring of the solar sunspot cycle.     

Atmospheric temperature profiling by joint Raman,Rayleigh and Fe Boltzmann lidar measurements

Simultaneous and complete temperature profiles from near ground to about 100 km are essential for studying the dynamical coupling between different atmospheric layers. They are acquired by combining three different lidar techniques at Wuhan, China (30.5°N, 114.4°E). The atmospheric temperatures from about 3 to 25 km are calculated from the nitrogen molecule density profiles obtained from the N₂ vibrational Raman backscatter, while the atmospheric temperatures between 30 and ∼75 km are calculated by the standard Rayleigh scattering method. The temperatures in the 80–100 km altitude region are derived from the Fe Boltzmann technique. The temperature profiles measured by our lidar systems exhibit good agreement when compared with the radiosonde and satellite data, as well as the model. A Lomb–Scargle spectral analysis of the normalized temperature perturbations in the altitude range from 4 to 60 km shows that the spectral slopes of the vertical wave number spectra tended to −3 for large vertical wave numbers. This is consistent with the model predictions of saturated gravity wave spectra.     

Interannual variability of mesospheric mean winds observed with the MU radar

In an effort to study the interannual variation of mesospheric (65–90 km altitude) mean winds, 10 years (1986–1995) of wind data collected with the MU radar at Shigaraki, Japan (34.9°N, 136.1°E) have been analysed. The analysis reveals that the mean zonal wind circulation in the mesosphere is dominated by an annual variation. The summer westward flow in the mesosphere shows a smooth variation with a peak value in the range 40–60 m/s in June/July. In contrast to the summer westward winds, the winter eastward winds exhibit much more variability. In some years it is found that the winds exceed even 60 m/s and the peak value may occur in any one of the winter months. Scrutiny of the duration of the summer westward winds reveals a two-year periodicity, which has been compared with the quasi-biennial oscillation (QBO) phases at the equator. The search for a dependence of the mean wind on solar activity does not reveal any indications of it. Ten-year averaged winds are compared with the model atmosphere, CIRA-86, values and certain agreements and disagreements are pointed out.