Relationship between lightning-storm characteristics , and both power and rate of lightning-discharge RF emissions observed by FORTE
Prior studies have noted a strongly nonlinear enhancement of lightning flash rates with increasing cloud height. Here we report a related observation, of a tendency for increased intracloud (IC)-discharge radioemission power versus increased height of the electrified cloud. We find that there is a strong statistical increase of effective radiated power (ERP, or isotropic peak power radiated from the source in the receiver bandwidth) of IC discharges, for increasing capping height of the parent storm. Thus a future satellite-based lightning monitor which triggers on only the most intense radio emissions will be strongly selective for electrified storms with very deep vertical development. Such storms are also indicated in severe convective weather. INTRODUCTION Why is thunderstorm height important to monitor? It is now widely accepted that thunderstorm electrification usually requires collisions between graupel (or hail) and ice crystals in the presence of supercooled water [see. e.g, the review in Baker et al., 1999]. Blythe et al [2001] have shown on the basis of scaling relationships that a thundercloud’s lightning flash rate (f) is expected to be “proportional to the product of the downward flux of solid precipitation (i.e, graupel and hail) through the body of the thundercloud and the upward flux of ice crystals into the anvil”. In a useful review on the electrification of severe storms, Williams [2001] (subsequently W2001) shows that having a sustained presence of mixed-phase-hydrometeors together in the same region requires the cloud to have deep vertical development: The cloud must extend upward to the -40 Celsius isotherm or thereabouts, and must implicitly contain an intense core updraft. The latter can lead to tropopause overshoot (see in particular Figure 13.14 of W2001) and thus to water vapor insertion into the normally dry stratosphere. Here we report on initial observations of a relationship between storm height and lightning vigor, with the lightning vigor being sensed by radio emissions. Given that the FORTE satellite carries neither a radar (like the TRMM PR) nor a microwave imager (like the TRMM TMI), our inference of storm height cannot derive from such non-lightning data, at least not on such data provided by FORTE itself. Instead, our inference is based on the distribution of lightning-discharge heights for each storm. In this present paper, we find that the radio ERP is a significant statistical correlate of storm height as inferred from contemporaneous FORTE RF data. Satellite RF lightning monitoring is able to measure the lightning-discharge height, not just the horizontal position (latitude, longitude). This ability is unique to the RF approach: The optical signature of lightning seen from space is a transient cloud-top brightening, regardless of where (in height) the lightning occurs in the atmospheric column underneath the cloud top. Optical photons are elastically Mie-scattered tens to hundreds of times, in what is effectively a diffusion process through the cloud [Koshak et al., 1994; Light et al., 2001] before emerging from the cloud top. By contrast, RF propagates through clouds with neither scattering nor attenuation. a future GPS-based RF monitor would use differential-time-of-arrival (DTOA) methods to retrieve not only the discharge plan location (longitude, latitude) but also the discharge altitude [Suszcynsky et al., 2000].
Diffusion model for lightning radiative transfer
A one-speed Boltzmann transport theory, with diffusion approximations, is applied to study the radiative transfer properties of lightning in optically thick thunderclouds. Near-infrared (lambda = 0.7774 micrometers) photons associated with a prominent oxygen emission triplet in the lightning spectrum are considered. Transient and spatially complex lightning radiation sources are placed inside a rectangular parallelepiped thundercloud geometry and the effects of multiple scattering are studied. The cloud is assumed to be composed of a homogeneous collection of identical spherical water droplets, each droplet a nearly conservative, anisotropic scatterer. Conceptually, we treat the thundercloud like a nuclear reactor, with photons replaced by neutrons, and utilize standard one-speed neutron diffusion techniques common in nuclear reactor analyses. Valid analytic results for the intensity distribution (expanded in spherical harmonics) are obtained for regions sufficiently far from sources. Model estimates of the arrival-time delay and pulse width broadening of lightning signals radiated from within the cloud are determined and the results are in good agreement with both experimental data and previous Monte Carlo estimates. Additional model studies of this kind will be used to study the general information content of cloud top lightning radiation signatures.
Introduction and experience with the primary mail services based on their names for students
Kyushu University provided mail service based on student IDs such as "1AB10123X" to the university students for many years. Using this model, we had problems communicating with the students who graduated from the University and enrolled in the graduate school. The students received new mail addresses based on their new student IDs such as "2AB12789Y". Faculty members were forced to change the student mail addresses in the mailing lists and in their mail client address book. Furthermore, students were forced to notify the e-mail address change to all of their existing contacts. We introduced a new mail system to provide addresses based on the student name, as well as student ID in April 2011. The new naming convention uses the following format: lastname.firstname.999 where 999 is a random number of 3 digits. Students can select some combination patterns of their first and last names for Japanese. We also consider the middle names for foreign students. In the system implementation, we did not have the formal information of alphabetical names for students. We generated alphabetical names from Japanese Katakana names. It is not easy for us to get the appropriate name in this manner. We implemented a confirmation stage of the alphabetical name at first use, and then students can select their mail addresses for their convenience. We paid much attention to the user interface in the system. Since April 2011, the number of users who use the mail address based on their own name has been increasing gradually. This paper will detail the usage status of the new system.