Moderate Resolution Imaging Spectroradiometer (MODIS) Level 2 observations from the Terra satellite are used to create a 3-yr climatology of cloud-top phase over a section of the Southern Ocean (south of Australia) and the North Pacific Ocean. The intent is to highlight the extensive presence of supercooled liquid water over the Southern Ocean region, particularly during summer. The phase of such clouds directly affects the absorbed shortwave radiation, which has recently been found to be ''poorly simulated in both state-of-theart reanalysis and coupled global climate models'' (Trenberth and Fasullo).The climatology finds that supercooled liquid water is present year-round in the low-altitude clouds across this section of the Southern Ocean. Further, the MODIS cloud phase algorithm identifies very few glaciated cloud tops at temperatures above 2208C, rather inferring a large portion of ''uncertain'' cloud tops. Between 508 and 608S during the summer, the albedo effect is compounded by a seasonal reduction in high-level cirrus. This is in direct contrast to the Bering Sea and Gulf of Alaska. Here MODIS finds a higher likelihood of observing warm liquid water clouds during summer and a reduction in the relative frequency of cloud tops within the 08 to 2208C temperature range.As the MODIS cloud phase product has limited ability to confidently identify cloud-top phase between 258 and 2258C, future research should include observations from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and other space-based sensors to help with the classification within this temperature range. Further, multiregion in situ verification of any remotely sensed observations is vital to further understanding the cloud phase processes.

An analysis of cloud seeding activity for the period 1960–2005 over a hydroelectric catchment (target) area located in central Tasmania, Australia, is presented. The analysis is performed using a double ratio on monthly area-averaged rainfall for the months of May–October. Results indicate that increases in monthly precipitation are observed within the target area relative to nearby controls during periods of cloud seeding activity. Ten independent tests were performed and all double ratios found are above unity with values that range from 5% to 14%. Nine out of 10 confidence intervals are entirely above unity and overlap in the range of 6%–11%. Nine tests obtain levels of significance >0.05 level. If the Bonferroni adjustment is made to account for multiple comparisons, six tests are found to be significant at the adjusted alpha level. Further field measurements of the cloud microphysics over this region are needed to provide a physical basis for these statistical results.

The cloud structure associated with two frontal passages over the Southern Ocean and Tasmania is investigated. The first event, during August 2006, is characterized by large quantities of supercooled liquid water and little ice. The second case, during October 2007, is more mixed phase. The Weather Research and Forecasting model (WRFV2.2.1) is evaluated using remote sensed and in situ observations within the post frontal air mass. The Thompson microphysics module is used to describe in-cloud processes, where ice is initiated using the Cooper parameterization at temperatures lower than 288C or at ice supersaturations greater than 8%. The evaluated cases are then used to numerically investigate the prevalence of supercooled and mixed-phase clouds over Tasmania and the ocean to the west. The simulations produce marine stratocumulus-like clouds with maximum heights of between 3 and 5 km. These are capped by weak temperature and strong moisture inversions. When the inversion is at temperatures warmer than 2108C, WRF produces widespread supercooled cloud fields with little glaciation. This is consistent with the limited in situ observations. When the inversion is at higher altitudes, allowing cooler cloud tops, glaciated (and to a lesser extent mixed phase) clouds are more common. The simulations are further explored to evaluate any orographic signature within the cloud structure over Tasmania. No consistent signature is found between the two cases.

A “climatology” of supercooled cloud tops is presented for southeastern Australia and the western United States, where historic glaciogenic cloud-seeding trials have been located. The climatology finds that supercooled cloud tops are common over the mountainous region of southeastern Australia and Tasmania (SEAT). Regions where cloud-seeding trials reported positive results coincide with a higher likelihood of observing supercooled cloud tops. Maximum absolute frequencies (AFs) occur ∼40% of the time during winter. There is a relationship between the underlying orography and the likelihood of observing supercooled liquid water (SLW)-topped clouds. Regions of the United States that have been the subject of cloud-seeding trials show lower AFs of SLW-topped clouds. The maximum is located over the Sierra Nevada and occurs ∼20% of the time during winter (Sierra Cooperative Pilot Project). These sites are on mountains with peaks higher than any found in SEAT (>3000 m). For the Sierra Nevada, the AF of SLW-topped clouds decreases as the elevation increases, with glaciation occurring at the higher elevations. The remote sensing of supercooled cloud tops is not proof of a region’s amenability for glaciogenic cloud seeding. This study simply highlights the significant environmental differences between historical cloud-seeding regions in the United States and Australia, suggesting that it is not reasonable to extrapolate results from one region to another. Without in situ cloud microphysical measurements, in-depth knowledge of the timing and duration of potentially seedable events, or knowledge of the synoptic forcing of such events, it is not possible to categorize a region’s potential for precipitation augmentation operations.

Understanding of wintertime precipitation in mountainous regions is central to water resources management in the Murray-Darling Basin. The Great Dividing Range (GDR), which runs along the entire eastern seaboard of the Australian continent, forms the headwaters of all of the major rivers in this agricultural 'breadbasket'. Annual precipitation amounts are up to four times greater in these uplifted regions compared with the lower lying plains to the west (Chubb et al. 2011), and the majority of this precipitation occurs in the cooler months of May-September. A decline of about 15 per cent in cool season precipitation in southern Australia since 1958 has been observed (Nicholls 2010), and links with sealevel pressure changes have been established (Larsen and Nicholls 2009), but the impact on alpine precipitation in this region has not been specifically investigated. Research into the meteorology of mountainous regions has failed to reach the level of interest in Australia that it has