Tree-ring records from New Zealand: long-term context for recent warming trend

 Distinct periods of warmth have been identified in instrumental records for New Zealand and the surrounding southwest Pacific over the past 120 years. Whether this warming is due to natural climate variability or the effects of increasing greenhouse gases is difficult to determine given the limited length of instrumental record. Longer records derived from tree rings can help reduce uncertainties in detection of possible causes of climatic change, although relatively few such records have been developed for the Southern Hemisphere. In this work, we describe five temperature-sensitive tree-ring width chronologies for New Zealand which place the recent warming trend into a long-term (pre-anthropogenic) context. Included are three pink pine (Halocarpus biformis) chronologies, two for Stewart Island and one for the North Island of New Zealand. Two silver pine (Lagarostrobus colensoi) series, one each from the North and South Islands, are updated from previous work. The length of record ranges from AD 1700 for Putara, North Island to AD 1400 for Ahaura, South Island. The pink and silver pine are different species from those used previously to reconstruct temperatures for New Zealand. All five chronologies are positively and significantly correlated with warm-season (November-April) individual station temperature records, a New Zealand-wide surface air temperature index and gridded land/marine temperatures for New Zealand and vicinity. The highest 20 and 40-year growth periods in all five tree-ring series coincide with the New Zealand temperature increase after 1950. An exception is found for the 40-year interval at Ahaura, the least temperature-sensitive of the five sites. A t-test comparison indicates that these recent growth intervals are significantly higher (0.01 to 0.0001 level) than any of those prior to the twentieth century for three of the five sites, dating as far back as AD 1500. The results suggest that the recent warming has been distinctive, although not clearly unprecedented, relative to temperature conditions inferred from tree-ring records of prior centuries. Received: 18 February 1997/Accepted: 11 September 1997     

IRON METEORITES OF GROUP IA AND IIA: STUDY OF PHOSPHIDE MORPHOLOGY ENHANCED BY DRY CI2 ETCHING

A method is described for etching iron meteorites by heating at 350 °C in dry chlorine gas. Iron is volatilized from low-nickel iron phases, e.g. kamacite, and the residual non-volatile chlorides are removed by solution. The study of the morphological character of the exposed phosphides on 16 specimens from Group IA and IIA showed no distinctive habit restricted to either group.     

X-ray confirmation of the new intermediate polar RX J1238–38

By finding a 2147-s X-ray pulsation in the recently identified ROSAT   source RX  1238–38 we confirm that it is a member of the intermediate polar class of cataclysmic variable. We analyse the spectral changes over the white dwarf spin cycle, but are unable to distinguish between competing mechanisms for the cause of the pulsation. RX  1238–38 has an anomalous ratio of spin period to orbital period, similar to that of EX Hya.     

RX J0744−52: a probable new intermediate polar

We present optical and X-ray data of the cataclysmic variable RX 0744−52 discovered using ROSAT by Motch et al. High-resolution spectroscopy centred on the Hα line indicates a probable orbital period of 3.60 h. From its distance (obtained using polarimetry), its X-ray luminosity, its X-ray colour and its X-ray/UV+optical ratio, we suggest that RX 0744−52 is a new intermediate polar. The absence of a significant coherent modulation in the X-ray light curve suggests either that RX 0744−52 has a low inclination or that the rotational and magnetic axes must be closely aligned. This is consistent with its small radial velocity amplitude.     

Stereoscopic observations of gamma rays at the Whipple observatory

Observations of photons at E ≥ 550 GeV from the Crab Nebula are presented and used to assess the potential of multi-telescope systems for γ-ray astronomy.

The Whipple observatory 10 m and 8 m imaging atmospheric erenkov telescopes have been used to provide a stereoscopic view of air showers to make a more complete measurement of air shower parameters. Here we present a measurement of the spread in the arrival direction of primary γ-rays originating from a point source. The data show that the shower arrival direction can be reconstructed with an accuracy of σ = 0.°14.     

The discovery of a persistent quasi-periodic oscillation in the intermediate polar TX Col

We report on the detection of an ∼5900 s quasi-periodic variation in the extensive photometry of TX Col spanning 12 yr. We discuss five different models to explain this period. We favour a mechanism where the quasi-periodic variation results from the beating of the Keplerian frequency of the 'blobs' orbiting in the outer accretion disc with the spin frequency and from modulated accretion of these 'blobs' taking place in a shocked region near the disc/magnetosphere boundary.     

Urban scale modelling: The Sydney hailstorm of 14 April 1999

Summary The aim of this study is to point to the very large improvements that are taking place in a range of modelling applications in the urban areas. The particular phenomenon chosen in this study is a supercell, but it could well have been any other aspect of urban modelling. The Sydney hailstorm of 14 April 1999 was a long-lived, high precipitation supercell that produced a massive damage bill of over 2 billion Australian dollars from its hail swath. The Sydney hailstorm was poorly forecast for a number of reasons including: the severe weather season had officially ended so there were no specialist staff on duty when the hailstorm struck Sydney; the storm proved very difficult to predict and it was expected to continue heading out to sea; and the forecast guidance from all available operational numerical models was inadequate at the resolution required for a supercell simulation. Here, our interest is on the last of the problems, namely, the quality of the operational numerical model guidance, especially given the impact it had on a densely populated urban region.In this study, we compare the numerical guidance available at the time with current modeling capability which, although in research mode at present, will soon be available in real-time mode. The operational models were hydrostatic models run at horizontal resolutions of 25km at best, compared with 1km horizontal resolution for the non-hydrostatic research model. The research model also had a high-order differencing scheme and a sophisticated six phase cloud physics scheme compared with the much simpler parameterized convection in the operational models. The operational model produced very little convective precipitation and it was displaced well to the north of Sydney. The research model generated a supercell with a track and a hail size distribution that was encouragingly close to the observed.