Diurnal variation in water vapor over North America and its implications for sampling errors in radiosonde humidity

Abstract

[1] Diurnal variations in atmospheric water vapor are studied by analyzing 30-min-averaged data of atmospheric precipitable water (PW) for 1996-2000 derived from Global Position System (GPS) observations from 54 North America stations. Vertical structures in the diurnal cycle of atmospheric water vapor are examined using 3-hourly radiosonde data from Lamont, Oklahoma, during the 1994 -2000 period. Significant diurnal variations of PW are found over most of the stations. The diurnal (24 hour) cycle, S 1 , which explains over 50% of the subdaily variance, has an amplitude of 1.0 -1.8 mm over most of the central and eastern United States during summer and is weaker in other seasons. The S 1 peaks around noon in winter and from midafternoon to midnight in summer. The semidiurnal (12 hour) cycle is generally weak, with an amplitude of a few tenths of 1 mm. At Lamont, specific humidity in the free troposphere is significantly higher in the early morning (0000 -0008 local solar time (LST)) than during the day (0800 -1800 LST). This diurnal variation changes little from $4 to 16 km above the ground. Near the surface, specific humidity tends to be lower in the morning than in the afternoon and evening in all seasons except summer. This near-surface diurnal cycle propagates upward through the lower troposphere (up to $4 km). Errors in seasonal mean humidity due to undersampling the diurnal cycle with twice-daily synoptic soundings (at 0000 and 1200 UTC) are generally small (within ±3% or ±0.5 mm for PW), but it can easily reach 5 -10% if there is only one random sounding per day. Several physical processes are proposed that could contribute to the diurnal variations in atmospheric water vapor.

Assessment of small-scale integrated water vapour variability during HOPE

“…This is a known characteristic of the near-real-time processing of GPS data, which is also seen in the investigation of the daily cycle at stations in North America by Dai (2002). The exact reason for this feature is not finally clarified yet and subject of ongoing investigation.…”

Diurnal cycle of precipitation over Fujian Province during the pre-summer rainy season in southern China

“…It results mainly from the solar heating in surface and atmosphere (Wallace 1975;Yang and Slingo 2001;Nesbitt and Zipser 2003;Yang and Smith 2006) and often referred to as atmospheric tides (Dai and Wang 1999). Most earlier studies have also revealed diurnal variations in moist convection and cloudiness (Sui et al 1997;Garreaud and Wallace, 1997;Yang and Slingo 2001), precipitation (Wallace 1975;Dai 2001a, b;Sorooshian et al 2002), and atmospheric water vapor (Dai et al 2002). These diurnal variations can affect the exchanges of energy (Bergman and Salby 1996), water (Trenberth et al 2003), and momentum (Dai and Deser 1999) fluxes between surface and atmosphere.…”

Diurnal variations in integrated water vapor derived from a GPS ground network in the Volga–Ural region of Russia

“…Currently studies of diurnal variations in GPS IWV for different areas are known (Dai et al, 2002;Glowacki et al, 2006;Jin et al, 2008;Ortiz de Galisteo et al, 2011). However, for assessment of the global water vapor content, some regions are insufficiently studied, which is particularly the case for Russia.…”