The satellite data for June-July 1997 at the Southern Great Plains site of the Atmospheric Radiation Measurement program are analyzed. The observed clouds are classified into high, midlevel and low clouds according to their top heights. For each cloud type, the contribution to the total fractional cloud cover from clouds of different sizes is determined using a Lagrangian cloud classification scheme. It is found that in the midlatitude continental, convectively active environment, more than half of the total cloud cover is from high clouds, of which 80% comes from clouds with area > 4 × 104 km2. For midlevel clouds, more than 50% of the contribution to cloud cover is from small clouds (e.g. cloud area < 4 x 104km2).. Almost all of the low clouds with significant contribution to cloud cover have spatial scales <4 × 104km2. This suggests that most of the midlevel and low clouds are of subgrid scale to a typical GCM resolution. We further found that cloud radiative properties, such as cloud albedo, outgoing longwave radiation and cloud radiative forcing, have strong scale dependence. Bigger clouds are brighter and have lower OLR. These results indicate that contributions to the observed cloud radiative forcing are dominated by large cloud systems.
`Real-world' applications of femtosecond pulses require laser sources that are reliable, compact, and easy-to-use. Diode-pumped lasers are one key step in this direction, and as a next key step we have developed and demonstrated a simple technique using semiconductor saturable absorbers to passively start and stabilize mode-locked lasers. Because the saturable absorber stabilizes soliton modelocking, we achieve self-starting modelocking over a wide cavity stability range, in contrast to KLM, which tends to require critical cavity alignment and is usually not self-starting. We discuss different saturable absorber designs. An A-FPSA is used in a diode-pumped Nd:glass laser (130 fs, 100 mW avg output power) and a Cr:LiSAF laser (45 fs, 80 mW output). A thin saturable absorber design provides self-starting mode- locking over a wavelength range of 30 nm, and a low-loss design supports a record mode- locked output power of 120 mW from a Cr:LiSAF laser. A dispersive saturable absorber mirror design combines both negative dispersion compensation and saturable absorption within one semiconductor device and produces a compact mode-locked Cr:LiSAF laser (160 fs, 25 mW) without the need of prisms for dispersion compensation. Finally, we present an optimized diode-pumped cavity layout for Cr:LiSAF which allows for higher output powers (> 1 W cw).
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