The micrometeoroid mass flux into the upper atmosphere: Arecibo results and a comparison with prior estimates

Radar micrometeor observations at Arecibo Observatory have enabled direct estimates of the meteoroid mass flux into the upper atmosphere. We report mass flux determinations from November 1997/1998 observations that are based on the observed number of meteor events per day in the 300-m diameter Arecibo beam and on particle mass determinations from that fraction of all particles for which deceleration is measured. The average mass of the Arecibo micrometeoroids that manifest observable deceleration is similar to0.32/0.76 mu gm/particle with a resultant annual whole-Earth mass flux of 1.6 x 10(6)/2.7 x 10(6) kg/yr over the similar to 10(-5) - 10(2) mu gm mass range for 1997/1998, respectively. The annual whole-earth mass flux per decade of particle mass is calculated and compared with that of Ceplecha et al. [1998] (3.7 x 10(6) kg/yr) and with that derived by Love and Brownlee [1993] (LB) from small particle impact craters on the orbital Long Duration Exposure Facility (LDEF). We also give the LDEF results as significantly modified using the Arecibo-determined average particle velocity of similar to 50 km/sec-much larger than the effective value of 12 km/sec used by LB. This modification results in a net LDEF mass flux of 1.8 x 10(6) kg/yr - 7% of the value we determined from reanalysis of the LB data using their original 12 km/sec mean impact speed. These results may provoke some debate.