Michael L. Hutchins

Grooming in primates: Implications for its utilitarian function

Captive lion-tailed macaques, ring-tailed lemurs and Celebes black “apes” performed relatively more social grooming of areas which are inaccessible to self-grooming. Combined with considerable circumstantial evidence, this suggests that primate grooming may subserve real utilitarian functions in parasite removal, in addition to its acknowledged social functions.

Highlights of a New Ground-Based, Hourly Global Lightning Climatology

The seasonally and diurnally varying frequency of lightning flashes provides a measure of the frequency of occurrence of intense convection and, as such, is useful in describing the Earths climate. Here we present a few highlights of a global lightning climatology based on data from the ground-based World Wide Lightning Location Network (WWLLN), for which global observations began in 2004. Because WWLLN monitors global lightning continuously, it samples ~100 times as many lightning strokes/flashes per year as the Tropical Rainfall Measuring Missions (TRMM) Lightning Imaging Sensor (LIS). Using WWLLN data it is possible to generate a global lightning climatology that captures seasonal variations, including those associated with the midlatitude storm tracks, and resolves the diurnal cycle, thereby illuminating the interplay between sea breezes, mountain–valley wind systems, and remotely forced gravity waves in touching off thunderstorms in a wide variety of geographical settings. The text of the paper sho...

Far-Field Power of Lightning Strokes as Measured by the World Wide Lightning Location Network

AbstractThe World Wide Lightning Location Network (WWLLN) is a long-range network capable of locating lightning strokes in space and time. While able to locate lightning to within a few kilometers and tens of microseconds, the network currently does not measure any characteristics of the strokes themselves. The capabilities of the network are expanded to allow for measurements of the far-field power from the root-mean-square electric field of the detected strokes in the 6–18-kHz band. This is accomplished by calibrating the network from a single well-calibrated station using a bootstrapping method. With this technique the global median stroke power seen by the network is 1.0 × 106 W, with an average uncertainty of 17%. The results are validated through comparison to the return-stroke peak current as measured by the New Zealand Lightning Detection Network and to the previous ground wave power measurements in the literature. The global median stroke power herein is found to be four orders of magnitude lower...

Diurnal variation of the global electric circuit from clustered thunderstorms

The diurnal variation of the global electric circuit is investigated using the World Wide Lightning Location Network (WWLLN), which has been shown to identify nearly all thunderstorms (using WWLLN data from 2005). To create an estimate of global electric circuit activity, a clustering algorithm is applied to the WWLLN data set to identify global thunderstorms from 2010 to 2013. Annual, seasonal, and regional thunderstorm activity is investigated in this new WWLLN thunderstorm data set in order to estimate the source behavior of the global electric circuit. Through the clustering algorithm, the total number of active thunderstorms are counted every 30 min creating a measure of the global electric circuit source function. The thunderstorm clusters are compared to precipitation radar data from the Tropical Rainfall Measurement Mission satellite and with case studies of thunderstorm evolution. The clustering algorithm reveals an average of 660 ± 70 thunderstorms active at any given time with a peak-to-peak variation of 36%. The highest number of thunderstorms occurs in November (720 ± 90), and the lowest number occurs in January (610 ± 80). Thunderstorm cluster and electrified storm cloud activity are combined with thunderstorm overflight current measurements to estimate the global electric circuit thunderstorm contribution current to be 1090 ± 70 A with a variation of 24%. By utilizing the global coverage and high time resolution of WWLLN, the total active thunderstorm count and current is shown to be less than previous estimates based on compiled climatologies.

Diurnal and Seasonal Lightning Variability over the Gulf Stream and the Gulf of Mexico

AbstractRecent observations from the World Wide Lightning Location Network (WWLLN) reveal a pronounced lightning maximum over the warm waters of the Gulf Stream that exhibits distinct diurnal and seasonal variability. Lightning is most frequent during summer (June–August). During afternoon and early evening, lightning is enhanced just onshore of the coast of the southeastern United States because of daytime heating of the land surface and the resulting sea-breeze circulations and convection. Near-surface wind observations from the Quick Scatterometer (QuikSCAT) satellite indicate divergence over the Gulf of Mexico and portions of the Gulf Stream at 1800 LT, at which time lightning activity is suppressed there. Lightning frequency exhibits a broad maximum over the Gulf Stream from evening through noon of the following day, and QuikSCAT wind observations at 0600 LT indicate low-level winds blowing away from the continent and converging over the Gulf Stream. Over the northern Gulf of Mexico, lightning is mos...

Diurnal Lightning Variability over the Maritime Continent: Impact of Low-Level Winds, Cloudiness, and the MJO

AbstractLightning over the Maritime Continent exhibits a pronounced diurnal cycle. Daytime and evening lightning occurs near coastlines and over mountain slopes, driven by sea and valley breezes. Nocturnal and morning thunderstorms are touched off where land breezes or mountain breezes converge or by gravity waves propagating away from regions of vigorous afternoon convection. In this study, the modulation of the diurnal cycle of lightning and precipitation by 850-hPa winds, cloudiness, and the Madden–Julian oscillation (MJO) is investigated using observations from the World Wide Lightning Location Network (WWLLN) and the Tropical Rainfall Measuring Mission (TRMM) satellite. The 850-hPa wind speed and area-averaged cloudiness are shown to be negatively correlated with day-to-day lightning frequency over land, and thunderstorm occurrence is suppressed windward of, and enhanced leeward of, mountain ranges. Lightning and environmental conditions are similarly related in the MJO. During break periods, the reg...

Daily and intraseasonal relationships between lightning and NO2 over the Maritime Continent

[1] The relationship between lightning and NO2 over Indonesia is examined on daily and intraseasonal time scales based on lightning observations from the World Wide Lightning Location Network (WWLLN) and tropospheric NO2 column densities from the Global Ozone Monitoring Experiment (GOME‐2) satellite mission. Composites of the daily NO2 observations regressed onto lightning frequency reveal a plume of enhanced NO2 following a day of enhanced lightning. Lightning and NO2 also vary coherently with the intraseasonal Madden‐Julian Oscillation (MJO) in a manner distinct from the cloudiness signature, with variations of up to ∼50% of the annual mean. Citation: Virts, K. S., J. A. Thornton, J. M. Wallace, M. L. Hutchins, R. H. Holzworth, and A. R. Jacobson (2011), Daily and intraseasonal relationships between lightning and NO2 over the Maritime Continent, Geophys. Res. Lett., 38, L19803, doi:10.1029/2011GL048578.

The world wide lightning location network (WWLLN): Update of status and applications

Powerful lightning flashes with large return stroke peak currents induce energetic and electrical coupling between the troposphere, the upper atmosphere and near-Earth space via the quasi-electrostatic and/or the radiated electromagnetic pulse (EMP) which leaks into space as whistler waves. Global lightning observations provide context on the activity levels of thunderstorm systems, assisting studies into whistler activity, Transient Luminous Events, Terrestrial Gamma-ray Flashes, meteorology and atmospheric electricity in general. One of the few scientific experiments which can currently provide such observations is the multi-station World Wide Lightning Location Network (WWLLN).

WWLLN lightning and satellite microwave radiometrics at 37 to 183 GHz: thunderstorms in the broad tropics†

We investigate lightning strokes and deep convection through the examination of cloud-to-ground (CG) lightning from the World Wide Lightning Location Network (WWLLN) and passive microwave radiometer data. Microwave channels at 37 to 183.3 GHz are provided by the Tropical Rainfall Measuring Mission satellite (TRMM) Microwave Imager (TMI) and the Special Sensor Microwave Imager/Sounder (SSMIS) on the Defense Meteorological Satellite Program (DMSP) satellite F16. The present study compares WWLLN stroke rates and minimum radiometer brightness temperatures (Tbs) for two northern and southern hemisphere summers (2009-2011) in the broad tropics (35° S to 35° N). To identify deep convection, we use lightning data and Tbs derived from all channels and differences in the Tbs (ΔTbs) of the three water vapor channels near 183.3 GHz. We find that stroke probabilities increase with increasing Tb depressions for all frequencies examined. Moreover, we apply methods that use the 183.3 GHz channels to pinpoint deep convection associated with lightning. High lightning stroke probabilities are found over land regions for both intense and relatively weak convective systems, although the TMI 85 GHz results should be used with caution as they are affected by a 7-km gap between the conical scans. Over the ocean, lightning is associated mostly with larger Tb depressions. Generally, our results support the noninductive thundercloud charging mechanism, but do not rule out the inductive mechanism during the mature stages of storms. Lastly, we present a case study in which lightning stroke rates are used to reconstruct microwave radiometer Tbs.

Design of a low cost mission to the Neptunian system

Visited only by Voyager 2 in 1989, Neptune and its moon Triton hold important clues to the formation and evolution of the solar system and exoplanetary systems. Neptune-sized planets are the most commonly discovered exoplanets to date. Neptune, an ice giant, is theorized to have migrated from its formation location in the early solar system. This migration affects the expected interior structure, composition, and dynamical evolution of the planet. Triton is conjectured to be a heavily-processed, captured Kuiper Belt Object (KBO), a remnant from the early solar nebula and unique in our solar system. Triton may possess a subsurface aqueous ocean, making it an important astrobiological target. The 2013-2022 Planetary Science Decadal Survey [1] identified a number of high priority science goals for the Neptunian system, including understanding the structure, composition, and dynamics of Neptunes atmosphere and magnetosphere, as well as surveying the surface of Triton. Following these guidelines, we present a low cost flyby mission concept to Neptune and Triton: TRIDENT (Taking Remote and In-situ Data to Explore Neptune and Triton). TRIDENT would carry six instruments and a government furnished atmospheric probe and would provide significant improvements over the scientific measurements undertaken by Voyager 2. In this paper, we first provide a detailed overview of the science questions pertaining to Neptune and Triton and of the science investigations necessary to elucidate them. We then present the design of TRIDENTs instrument suite, the trajectory and the spacecraft, as well as the motivation behind each of our choices. In particular, we demonstrate that, for a mission launched on an Atlas V 551, a Neptune orbiter mission would be infeasible with current technology levels without the use of aerocapture. We therefore present a flyby mission concept with a cost lower than FY2015