A parameter to evaluate the potential for tropical cyclone formation (genesis) in the North Atlantic between Africa and the Caribbean islands is developed. Climatologically, this region is the source of about 40% of the Atlantic basin tropical cyclones but roughly 60% of the major hurricanes. The genesis parameter is the product of appropriately scaled 5-day running mean vertical shear, vertical instability, and midlevel moisture variables. The instability and shear variables are calculated from operational NCEP analyses, and the midlevel moisture variable is determined from cloud-cleared GOES water vapor imagery. The average shear and instability variables from 1991 to 1999 and moisture variable from 1995 to 1999 indicate that tropical cyclone formation in the early part of the season is limited by the vertical instability and midlevel moisture. Formation at the end of the season is limited by the vertical shear. On average, there is only a short period from mid-July to mid-October when all three variables are favorable for development. This observation helps explains why tropical cyclone formation in the tropical Atlantic has such a peaked distribution in time. The parameter also helps explain intra-and interseasonal variability in tropical cyclone formation. An independent evaluation of the parameter and possible applications to operational forecasting are presented using data from the 2000 hurricane season. The possibility of determining additional thermodynamic information from the GOES sounder is also discussed.

[1] A technique for improved detection of airborne volcanic ash has been developed that uses three infrared (IR) bands from meteorological satellites. The three IR bands are centered near 3.9, 10.7, and 12.0 mm wavelength. The technique is based on the sum of two brightness temperature differences (BTDs), scaled to maximize the brightness and contrast of volcanic ash in the output image. The physical effects attributed to the observed BTDs that help distinguish the volcanic ash from various meteorological cloud types are (1) differential absorption by volcanic ash or sulfur dioxide at 3.9 mm, 10.7 mm, and 12.0 mm and (2) strong solar reflectance by ash at 3.9 mm, which varies diurnally. On the basis of two examples using data from the Geostationary Operational Environmental Satellite (GOES) the three-band IR technique is shown to provide better discrimination of volcanic ash from meteorological clouds than is possible using existing two-band methods. This conclusion is supported by comparisons of brightness count profiles and estimation of false ash detection rate statistics. The best results from the three-band IR technique are obtained during daylight hours over any surface, and at night when the ash cloud is over the ocean or other large body of water. The three-band IR technique is one of the tools currently being employed operationally at the Washington Volcanic Ash Advisory Center.

The aim of this study was to identify clear air boundaries and to obtain spatial distribution of convective areas associated with the sea breeze over the Iberian Mediterranean zone and the isle of Mallorca, both in Spain. Daytime Advanced Very High Resolution Radiometer (AVHRR) data from National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites were collected for May-October 2004. A cloud detection algorithm was used to identify clouds to derive daytime sea-breeze cloud frequency composites over land. The high-resolution composites aided in identifying the location of five preferential seabreeze convergence zones (SBCZ) in relation to the shape of coastline and orographic effects. Additionally, eight regimes were designated using mean boundary layer wind speed and direction to provide statistics about the effect of prevailing large-scale flows on sea-breeze convection over the five SBCZ. The offshore SW to W and the NW to N regimes were characterized by high cloud frequencies parallel to the coast. Small differences in mean cloud frequency values from morning to afternoon composites were detected with these regimes because sea-breeze fronts tended to form early and persist into the afternoon. Just the opposite occurred under the onshore NE to E and SE to S regimes. It was found that light to moderate (#5.1 m s 21 ) winds aloft result in more clouds at the leading edge of sea breezes. In contrast, strong synoptic-scale (.5.1 m s 21 ) flows weaken boundary layer convergence. The results from this satellite meteorology study could have practical applications for many people including those that forecast the weather and those that use the forecast for making decisions related to energy use, fishing, recreation, or agriculture activities, as well as for estimating pollution or issuing warnings for heavy rain or flash flooding.

Timberline ecotone (TE) generally developed because the temperatures in the environment were too low. There are other overlapping biotic and abiotic factors which affect the TE. The main aim of this work was to determine how the asymmetry of Babia Góra's ridge influences the location and characteristics of the timberline ecotone nowadays, and how the ridge influenced the timberline ecotone in the mid-20th century. The asymmetry of environmental conditions means the timberline has formed in two extreme environments: on the sunny and gentle southern slope (40% of the timberline length) and on the cold, humid, steep northern slope (another 40% of the timberline length). The southern slope of the ridge shows a progressive timberline length of 86%. In turn, 81% of the timberline on the northern slope is in a stable ecotone.

GOES-8 visible and infrared cloud frequency composites have been created from imagery collected during June, July, and August for the years 1996-99 over northern Florida. These cloud frequency composites are unique because they offer high-resolution coverage over a small area and have been tailored to address forecast needs. Both monthly and regime cloud frequency composites are presented. Nine regimes were designated to reflect the strength and development of the sea-breeze front under various synoptic winds and the resulting effect on convective development. The regimes were designated by mean boundary layer wind speed and direction over the region of interest. Results from four of the regimes are presented.A total of 222 days (60% of all possible days) were designated for the various wind regimes. Regime 4 (W to SW flow) occurred most frequently (24%) and had the most widespread distribution of higher cloud frequency, occurring both near the coast and inland. Regime 2, with contrasting E to NE flow, was the next most frequently occurring regime (17%) and had lower cloud frequencies, particularly inland in Alabama and Georgia. Regime 5, with strong W to SW flow (15%, not presented) was third, followed by Regime 8 with N to NW flow (13%) and Regime 1 (11%) with light and variable or light SE flow.The monthly composites included the days from the various regime days as well as those with a completely disturbed or completely suppressed sea-breeze circulation. Nonetheless, the influence of the sea-breeze circulation can readily be seen in the diurnal progression of cloud frequency over a month. The variations seen in monthly cloud frequency composites for June, July, and August 1996-99 highlight periods of high and low cloud frequency and offer a different perspective on year-to-year and month-to-month variability.The regime cloud frequency results are actively being used during the summer season in aviation and public forecasting to supplement available information.

ABSTRACT:A daytime over land multispectral cloud detection algorithm is presented to derive accurate convective cloud climatologies with high spatial resolution (1.1 km) over the Iberian Peninsula (IP) and the Balearic Islands (BI). The cloud detection scheme was designed to process Advanced Very High Resolution Radiometer (AVHRR) HRPT data and is tested here on NOAA-17 morning (0900-1200 UTC) and NOAA-16 afternoon (1200-1500 UTC) overpasses for the warm 6-month study period May-October. The algorithm consists of four spectral threshold tests applied to each pixel. Test 1 corresponds to the snow-ice removal, test 2 is the thermal infrared test, test 3 is the albedo or visible test and test 4 is the ratio between near-infrared and visible channels. The algorithm discretizes all AVHRR data into four groups called cloud-filled, cloud-free, snow-ice and snow-free radiances. The high-resolution convective cloud masks are obtained by subtracting snow-ice pixels from cloudy ones. In this article, a detailed description of the convective cloud detection scheme and the sources of error detected for each test are given, and the first seasonal and monthly regional convective cloud frequency composites are presented. Future applications of the newly proposed threshold algorithm in climate and meteorology are also discussed in this article, particularly the production of convective cloud composites for climate monitoring of storms over the IP and BI.

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