Seasonal and Local Solar Time Variation of the Meridional Wind at 95 km from Observations of the 11.072-GHz Ozone Line and the 557.7-nm Oxygen Line The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation Rogers, Alan E. E. et al. “Seasonal and Local Solar Time Variation of the Meridional Wind at 95 Km from Observations of the 11.072-GHz Ozone Line and the 557.7-Nm Oxygen Line.” Journal of Atmospheric and Oceanic Technology 33.7 (2016): 1355–1361. © 2016 American Meteorological Society As Published http://dx.doi.org/10.1175/jtech-d-15-0247.1 Publisher American Meteorological Society Version Final published version Citable link http://hdl.handle.net/1721.1/107662 Terms of Use Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. JULY 2016 R O G E R S E T A L . 1355 Seasonal and Local Solar Time Variation of the Meridional Wind at 95km from Observations of the 11.072-GHz Ozone Line and the 557.7-nm Oxygen Line ALAN E. E. ROGERS,PHILIP J. ERICKSON, AND LARISA P. GONCHARENKO Haystack Observatory, Massachusetts Institute of Technology, Westford, Massachusetts OMAR B. ALAM School of Applied and Engineering Physics, Cornell University, Ithaca, New York a JOHN NOTO,ROBERT B. KERR, AND SUDHA KAPALI Scientific Solutions, Inc., North Chelmsford, Massachusetts (Manuscript received 8 December 2015, in final form 31 March 2016) ABSTRACT Ground-based spectrometers have been deployed to measure the concentration, velocity, and temperature of ozone in the mesosphere and lower thermosphere (MLT), using low-cost satellite television electronics to observe the 11.072-GHz line of ozone. The ozone line was observed at an altitude near 95 km at 388N, 718W using three spectrometers located at the Massachusetts Institute of Technology’s Haystack Observatory (Westford, Massa- chusetts), Chelmsford High School (Chelmsford, Massachusetts), and Union College (Schenectady, New York), each pointed south at 88 elevation. Observations from 2009 through 2014 were used to derive the nightly averaged seasonal variation of the 95-km altitude meridional wind velocity, as well as the seasonally averaged variation of the meridional wind with local solar time. The results indicate a seasonal trend in which the winds at 95 km are directed 2 2 southward at about 10 m s 1 in the summer of the Northern Hemisphere and northward at about 10 m s 1 in the winter. Nighttime data from 25to15 local solar time show a gradual transition of the meridional wind velocity 2 from about 220 to 20 m s 1. These variations correlate well with nighttime wind measurements using 557.7-nm optical airglow observations from the Millstone Hill high-resolution Fábry–Perot interferometer (FPI) in Westford. 1. Introduction goal of providing locally acquired data to aid in the teaching of data analysis methods and statistics to high school stu- The Mesospheric Ozone System for Atmospheric In- dents, MOSAIC provides an ongoing source of science- vestigations in the Classroom (MOSAIC) is an educational quality data on mesospheric ozone variations, and the data project focused on ground-based observations of the rela- are publicly available online.1 The ozone in the upper me- tively weak microwave line of ozone at 11.072 454 5 GHz sosphere is measured by MOSAIC using a satellite TV low- (Pickett et al. 1998) in the upper mesosphere using low-cost noise block downconverter, followed by an intermediate satellite television (TV) electronics. Along with its primary frequency downconverter and analog-to-digital converter. To increase the strength of the line, the antenna beam is pointed an elevation of 88 to increase the pathlength Denotes Open Access content. through the atmosphere. The ozone in the upper meso- sphere is at low pressure, so a narrow Doppler broadened line originating from an altitude of about 95 km stands out a Current affiliation: Scientific Computing, Inc., Springfield, Virginia. Corresponding author address: Alan E. E. Rogers, Haystack 1 MOSAIC data are archived in the Madrigal distributed data- Observatory, Massachusetts Institute of Technology, Off Route 40, base system, supported by the U.S. National Science Foundation’s Westford, MA 01886-1299. Atmospheric and Geospace Sciences directorate for atmospheric E-mail: [email protected] studies (http://madrigal.haystack.mit.edu/). DOI: 10.1175/JTECH-D-15-0247.1 Ó 2016 American Meteorological Society 1356 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VOLUME 33 from the pressure-broadened line from the ozone at lower altitudes. In this paper we assume a nominal altitude for the secondary maximum of the nighttime ozone to be 95 km (Smith and Marsh 2005). We also assume based on satellite measurements (Gao et al. 2012) that the 557.7-nm oxygen line originates from the same altitude. A complete de- scription of the instrument and measurements of the sea- sonal and diurnal variations of ozone near the mesopause for data collected in 2008 were reported by Rogers et al. (2009). The repeatability of seasonal mesospheric ozone variations from 2008 through 2011 at six sites in the north- eastern United States was reported by Rogers et al. (2012). While the observed line is only about 20 mK out of a background system noise of about 100 K, it is never- theless possible to estimate the average velocity of the ozone from the small shift in the line center frequency due to the Doppler shift from the wind at 95 km. In this paper, we report the average nighttime mesospheric wind from three spectrometers located at the Massachusetts Institute of Technology (MIT)’s Haystack Observatory (Westford, Massachusetts), Chelmsford High School (Chelmsford, Massachusetts), and Union College (Sche- nectady, New York) using data from 2010 through 2014. These sites have their antenna beams pointing south, al- FIG. 1. Seasonal trend in the average velocity of ozone at night. The error bars are 61s. lowing the measurement of the meridional wind at a latitude of 388N and a longitude around 718W, where the antenna beams intersect the region at 95 km. velocity data during nighttime only (Rogers et al. 2009). Daytime data are not available due to the an- nihilation of most of the ozone at 95 km by ultraviolet 2. Instrumentation photons from the sun. This reduces the opacity by a The velocity data were acquired from a network of factor of about 10 (Smith and Marsh 2005) and reduces three ozone spectrometers located at the MIT Hay- the signal to a few millikelvins, resulting in an in- stack Observatory (42.6188N, 71.4988W), Union Col- sufficient signal-to-noise ratio (SNR). lege (42.8178N, 73.9288W), and Chelmsford High Information on the temperature of the ozone in the School (42.6198N, 71.3678W). The spectrometers are mesosphere and lower thermosphere (MLT) can be pointed at azimuths 1908,1808, and 1728, respectively. obtained from the line shape near the peak, where the The beam of each spectrometer physically intersects width is determined primarily from the Doppler the ozone layer at 95 km at 388N, 718W, which is in the broadening of the ozone above about 90 km. However, Atlantic Ocean about 200 km off the coast of Maryland. the results we report in this paper are obtained from Data at Haystack were taken from 24 January 2009 single-channel spectrometers for which the SNR is in- through 13 August 2014. Data at Union College were sufficient to obtain measurements of temperature with taken from 19 February 2009 through 8 June 2015. Fi- integration times of less than several weeks. In the fu- nally, data at Chelmsford High School were taken from ture, following the spectrometer enhancements, which 25 December 2011 through 8 June 2015. The three will be discussed in section 6, we may be able to obtain spectrometers use temperature-controlled oven crystal temperatures on time scales of geophysical relevance. oscillators at 10 MHz as a frequency reference. Tests were made of the accuracy of the reference by 3. Results injecting a test signal at 11.072 454 5 GHz from a syn- thesizer whose reference had been checked against an Figures 1 and 2 show velocity data from the MOSAIC atomic clock. The accuracy of the frequency control of spectrometers at Haystack, Union, and Chelmsford. By the ozone spectrometers was estimated to be within 7 convention, negative velocities denote winds directed parts in 109, corresponding to a line-of-sight velocity southward (northerly wind), and positive velocities de- 2 accuracy of 2 m s 1. Ozone spectrometers collect wind note winds directed northward (southerly wind). To JULY 2016 R O G E R S E T A L . 1357 significant given the large instrumental noise in the ozone data, it could be related to a longer time coverage by the Haystack spectrometer (2009–15) that includes a period of very low solar activity and potential de- pendence of MLT winds on solar activity or quasi- biennial oscillation (Forbes et al. 2008; Oberheide et al. 2009). In addition, a frequency error could be re- sponsible. The Haystack spectrometer electronics is the only one of the network’s three spectrometers whose data are used in this paper that is located in an unheated building. The new spectrometers will be equipped with a stable frequency reference as will be discussed in section 6. Figure 2 reveals significant local time variation, in that there are southward winds from 25 through 11 h local solar time, and northward winds from 12 through 15h. The transition point appears to be within 2 h after mid- night, and the full transition is from about 220 2 to 125 m s 1 in amplitude.