Simulation of heavy precipitation episode over eastern Peninsular Malaysia using MM5: sensitivity to cumulus parameterization schemes

A comparative study has been conducted to investigate the skill of four convection parameterization schemes, namely the Anthes–Kuo (AK), the Betts–Miller (BM), the Kain–Fritsch (KF), and the Grell (GR) schemes in the numerical simulation of an extreme precipitation episode over eastern Peninsular Malaysia using the Pennsylvania State University—National Center for Atmospheric Research Center (PSU-NCAR) Fifth Generation Mesoscale Model (MM5). The event is a commonly occurring westward propagating tropical depression weather system during a boreal winter resulting from an interaction between a cold surge and the quasi-stationary Borneo vortex. The model setup and other physical parameterizations are identical in all experiments and hence any difference in the simulation performance could be associated with the cumulus parameterization scheme used. From the predicted rainfall and structure of the storm, it is clear that the BM scheme has an edge over the other schemes. The rainfall intensity and spatial distribution were reasonably well simulated compared to observations. The BM scheme was also better in resolving the horizontal and vertical structures of the storm. Most of the rainfall simulated by the BM simulation was of the convective type. The failure of other schemes (AK, GR and KF) in simulating the event may be attributed to the trigger function, closure assumption, and precipitation scheme. On the other hand, the appropriateness of the BM scheme for this episode may not be generalized for other episodes or convective environments.     

Crustal volatile release at Merapi volcano; the 2006 earthquake and eruption events

High‐temperature gas in volcanic island arcs is widely considered to originate predominantly from the mantle wedge and from subducted sediments of the down‐going slab. Over the decade (1994–2005) prior to the 2006 eruption of Merapi volcano, summit fumarole CO₂ gas δ¹³C ratios are relatively constant at ?4.1 ± 0.3‰. In contrast, CO₂ samples taken during the 2006 eruption and after the May 26th 2006 Yogyakarta earthquake (M6.4) show a dramatic increase in carbon isotope ratios to ?2.4 ± 0.2‰. Directly following the earthquake (hypocentre depth 10–15 km), a 3–5‐fold increase in eruptive intensity was observed. The elevated carbon isotope gas data and the mid‐crustal depth of the earthquake source are consistent with crustal volatile components having been added during the 2006 events, most probably by the thick local limestone basement beneath Merapi. This ‘extra’ crustal gas likely played an important role in modifying the 2006 eruptive behaviour at Merapi and it appears that crustal volatiles are able to intensify and maintain eruptions independently of traditional magmatic recharge and fractionation processes.     

First Results from the Soho Ultraviolet Coronagraph Spectrometer

The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is being used to observe the extended solar corona from 1.25 to 10 R⊙ from Sun center. Initial observations of polar coronal holes and equatorial streamers are described. The observations include measurements of spectral line profiles for HI Lα and Lβ, Ovi 1032 Å and 1037 Å, Mgx 625 Å, Fexii 1242 Å and several others. Intensities for Mgx 610 Å, Sixii 499 Å, and 520 Å, Sx 1196 Å, and 22 others have been observed. Preliminary results for derived H⁰, O⁵⁺, Mg₉₊, and Fe¹¹⁺ velocity distributions and initial indications of outflow velocities for O⁵⁺ are described. In streamers, the H⁰ velocity distribution along the line of sight (specified by the value at e^-1, along the line of sight) decreases from a maximum value of about 180 km s^-1 at 2 R⊙ to about 140 km s^-1 at 8 R⊙. The value for O⁵⁺ increases with height reaching a value of 150 km s^-1 at 4.7 R⊙. In polar coronal holes, the O⁵⁺ velocity at e^-1 is about equal to that of H⁰ at 1.7 R⊙ and significantly larger at 2.1 R⊙. The O⁵⁺ in both streamers and coronal holes were found to have anisotropic velocity distributions with the smaller values in the radial direction.     

The cosmological constant—a brief history and recent results

We briefly review the history of the cosmological constant. Recently discovered accelerated expansion epoch of the universe placed the problem of the cosmological constant at a forefront of interest of astronomers and physicists. Short account of recent developments is given.     

Geomorphic setting and geohazard-related features along the Ionian Calabrian margin between Capo Spartivento and Capo Rizzuto (Italy)

The aim of this work is to describe the morpho-dynamic processes of coastal and submarine areas based on morpho-bathymetric data and sub-bottom acoustic profiles from the Calabrian Ionian margin (from Capo Spartivento to Capo Rizzuto). We describe some of the most significant geo-hazard features and show some examples of their complex interactions and related potential risk. The relationship between these geo-hazard features and the active tectonics and some severe historical earthquakes and tsunamis is also discussed. The studied area is characterized by several well developed canyon systems. The retrogressive erosion of the canyon heads affects the continental shelf and interacts with the coastal morpho-sedimentary processes, evidencing the intense geomorphic activity of this sector of Ionian margin. The widespread evidence of mass wasting processes and slope instability, together with the historical seismicity, makes this area also an ideal case study for investigating on the possible relationship between earthquakes and landslide-triggered tsunamis and assessing the potential risk.     

Eleven-years inversion of the green corona emission

A cross-correlation analysis of coronal green line intensity (5303 Å) and interplanetary magnetic field polarity for the period 1947–1970 shows that the coronal features are organized in a constant pattern with respect to the 4-sector structure through the solar cycle. A sudden inversion of the coronal pattern with respect to the sector structure takes place at the solar minima. The high emission regions of the green corona are located near the solar magnetic sector boundaries having polarities (?, +), (+, ?), (?, +) during cycles 18, 19, 20 respectively in the northern hemisphere, and (+, ?), (?, +), (+, ?) in the southern hemisphere.     

Microwave,ultraviolet, and soft X-Ray observations of hale region 16898

Hale region 16898 was observed by the Westerbork Synthesis Radio Telescope at 6 cm and by the Ultraviolet Spectrometer and Polarimeter and the X-Ray Spectrometer on the Solar Maximum Mission satellite. Optical pictures of the same active region were taken at Sacramento Peak, Big Bear, and Meudon Observatories. The radio emission mechanisms are identified by comparing radio data with ultraviolet and soft X-ray data. The height of the radio sources and the magnetic field strength at that height are deduced. A radio source above a large sunspot shows a crescent shaped depression of circular polarization and a high brightness temperature. The emission mechanism is identified as gyroresonance at the second and the third harmonic layers and it is found that the second harmonic layer, where the magnetic field strength is 900 G, must be in the corona. An extended loop-like source connecting the leading and the following part of the active region as well as the sources associated with small spots are mainly due to thermal free-free emission by hot and dense plasma which is also observed in ultraviolet and soft X-ray radiation. The calculated radio brightness temperature, using the physical parameters deduced from the ultraviolet and soft X-ray line intensities, agrees with the observed brightness temperature. The height of the low brightness temperature sources above the small spots is 6000 ± 3000 km and that above the large spot is less than 3000 km: the source above the large spot does not show any shift relative to the sunspot due to the projection effect. Very strong radio emission was found which was associated with the merging of a group of small spots into the large sunspot. In the same day, warm ( 10⁶ K) and dense matter was present above the large spot. Evidence for nonthermal emission is presented.