Atmospheric Sounding Systems Atmospheric Instrumentation M. D. Eastin

Outline Sounding Systems Review of Atmospheric Soundings “Upsondes” (Weather Balloons) Balloon Sensor Package Navigation / Telemetry System Wind Estimation Exposure Errors “Downsondes” (GPS Dropsondes) Experimental Sounding Systems Atmospheric Instrumentation M. D. Eastin

Review of Atmospheric Soundings Definition and Concepts: Goal: Obtain a near-vertical profile of atmospheric pressure, temperature, humidity, and wind structure for use in both nowcasting and forecasting of convection, as well as the assimilation into global and regional numerical forecast models Methods: Balloon-based radiosondes ** Aircraft-based radiosondes ** Commercial Aircraft Remote Sensing ** ** Instrument: Radiosonde Atmospheric Instrumentation M. D. Eastin

Balloon Inflation Area Review of Atmospheric Soundings Latex Balloon (helium) Parachute Sensor Package Components of a Radiosonde Sounding System: 1. Balloon (with gas) / Parachute 2. Atmospheric Sensor Package 3. Navigation / Telemetry (GPS, transmitter, receiver) 4. Analysis Software Receiving Antenna Balloon Inflation Area Helium Tanks Atmospheric Instrumentation M. D. Eastin

Review of Atmospheric Soundings Common Data Collected by Radiosondes: 1. Parameters: Pressure Temperature Humidity Altitude / Time (determined from navigation satellites) Latitude / Longitude (determined from navigation satellites) Wind Speed / Direction (calculated from sequential locations) 2. Mandatory Levels: Atmospheric altitude/pressure levels at which all radiosondes are required to report current observations Tropospheric Levels (12) → Surface, 1000-mb, 925-mb, 850-mb, 700-mb, 500-mb, 400-mb, 300-mb, 250-mb, 200-mb, 150-mb, 100-mb 3. Significant Levels: Additional pressure levels at which a parameter experiences a vertical gradient change (Ex: lapse rate changes sign) Temperature begins to increase / decrease with height Humidity begins to increase / decrease with height Wind speed begins to increase / decrease with height Atmospheric Instrumentation M. D. Eastin

Review of Atmospheric Soundings Display / Analysis of Radiosonde Sounding Data: 1. Skew-T Log-P diagram Temperature plotted vs. pressure (usually in red) Dewpoint plotted vs. pressure (usually in blue or green) Wind speed and direction plotted vs. pressure (using barbs or a hodograph) Atmospheric Instrumentation M. D. Eastin

Review of Atmospheric Soundings Display / Analysis of Radiosonde Sounding Data: 2. Lifted Parcels and Stability Indices a. Surface Layer b. Mixed Layer Lifted Condensation Level (LCL) Level of Free Convection (LFC) Equilibrium Level (EL) Convective Inhibition (CIN) Convective Available Potential Energy (CAPE) Lifted Index (LI) Showalter Index (SI) K-Index (K) SWEAT Index T Td LCL LFC Tp < Te Tp > Te EL CIN CAPE Thermodynamic “path” of a lifted parcel from the surface Atmospheric Instrumentation M. D. Eastin

Review of Atmospheric Soundings Display / Analysis of Radiosonde Sounding Data: 3. Calculation of Thermodynamic Quantities Mixing ratio (w) Saturation mixing ratio (ws) Relative humidity (r) Specific humidity (q) Potential temperature (θ) Wet-bulb temperature (Tw) Given: P = 800 mb T = +9.5ºC Td = –8.0ºC Temperature at the LCL (TLCL) Pressure at the LCL (PLCL) Wet-bulb potential temperature (θw) Pseudo-adiabatic equivalent potential temperature (θe) Td, w P = 1000 mb T, wsw P = 800 mb θw TLCL θep θ Tw PLCL Atmospheric Instrumentation M. D. Eastin

Review of Atmospheric Soundings Uses of Radiosonde Sounding Data: Severe Weather Forecasting Atmospheric Instrumentation M. D. Eastin

Analysis of Radiosonde Observations Review of Atmospheric Soundings Uses of Radiosonde Sounding Data: Assimilation into Numerical Models Analysis of Radiosonde Observations Numerical Model Field Atmospheric Instrumentation M. D. Eastin

Upsondes – Weather Balloons The Balloon: Expandable latex weighing 200 – 1000 g Inflated with a “lift gas” less dense than air: 1. Helium (inert but becoming rare) 2. Hydrogen (explosive but common) Balloon (with a radiosonde package attached) ascends and expands (volume increases) until it reaches burst altitude (in the stratosphere) and then the radiosonde package descends by parachute → very few are recovered Balloon Diameter during Ascent: Balloon volume, diameter, and lift gas density are inversely proportional air density where: VBZ = balloon volume at height z (m3) VBO = balloon volume at the surface (m3) ρZ = air density at height z (kg m-3) ρO = air density at the surface (kg m-3) ρBZ = lift gas density at height z (kg m-3) ρBO = lift gas density at surface (kg m-3) DBZ = balloon diameter at height z (m) DBO = balloon diameter at the surface (m) Latex Balloon (helium) Parachute Instrument Package Atmospheric Instrumentation M. D. Eastin

Upsondes – Weather Balloons Balloon Ascent Rate: Balance between upward-directed free lift force (FL) and downward-directed drag force (FD) where: DBZ = balloon diameter at height z (m) ρZ = air density at height z (kg m-3) ρBZ = density of lift gas at height z (kg m-3) mB = balloon mass (kg) mP = sensor package mass (kg) g = gravity (m s-2) CD = drag coefficient (none) wB = balloon vertical velocity (m s-1) If we solve for the balloon’s vertical velocity If the vertical profile of air density is known (or can be reasonably estimated), then the the balloon’s expected diameter and vertical velocity can be calculated as a function of altitude (in a future homework) Atmospheric Instrumentation M. D. Eastin

Upsondes – Weather Balloons Balloon Ascent Rate: Tropospheric ascent rates are typically 5-6 m/s The balloon’s vertical velocity deviates slightly from this expectation for several reasons: 1. The balloon material is not perfectly elastic 2. A small portion of the lift gas will leak out 3. The internal lift gas temperature will become warmer than then ambient air 4. Balloon shape is not perfectly spherical 5. Vertical air motions will impact ascent rate 6. Drag coefficient is not constant Standard U.S. Weather Balloon Specifications: Manufacturer / Model: Vaisala RS-92 Lift Gas: Helium Balloon Mass: 250 g Sensor Package Mass: 280 g Operating Time: 135 minutes Atmospheric Instrumentation M. D. Eastin

Upsondes – Weather Balloons Sensor Package: Vaisala RS-92 Barometer: Aneroid silicon capsule Accuracy: ±0.4 mb Resolution: 0.1 mb Dynamic Range: 3 – 1080 mb Response Time: < 1 s Thermometer: Platinum resistance thermistor Accuracy: ±0.3°C Resolution: 0.1°C Dynamic Range: –90°C to +60°C Hygrometers: Twin-heated film-capacitance hygristors Accuracy: ±5.0% Resolution: 1.0% Dynamic Range: 0 – 100% Response Time: < 20 s (due to heating cycle) Temperature Sensor Humidity Sensors Pressure (inside) Atmospheric Instrumentation M. D. Eastin

Upsondes – Weather Balloons Navigation / Telemetry System: Vaisala RS-92 Sonde location is determined through simultaneous triangulation with at least four GPS satellites (more satellites increase position accuracy) The sonde transmits the detected GPS signals down to the ground station (which also receives GPS signals directly from the satellites) The ground station then computes the sonde position relative to the ground station position GPS Antenna: Code-correlating receiver Channels: 12 (maximum) Position Accuracy: ±10 m (horizontal) ±20 m (vertical) Wind Accuracy: 0.2 m/s Telemetry Antenna: Synthesized digital multiplexer Frequency: 403 MHz Data Downlink: 2400 bits/s Data Cycle: 1 s GPS Antenna Telemetry Atmospheric Instrumentation M. D. Eastin

Upsondes – Weather Balloons Wind Profile Estimation: Since balloons are characterized by large surface area and small mass, they usually follow the mean wind flow, and thus horizontal winds can be determined by tracking the balloon’s position during its ascent relative to the ground station’s position where: x = east-west distance (m) y = north-south distance (m) z = altitude (m) ϕ = elevation angle (degrees) θ = azimuth angle (degrees) Δt = time interval (s) u = zonal wind component (m s-1) v = meridional wind component (m s-1) The vertical winds are rarely computed since vertical position errors are larger and precise ascent rate is unknown z R Balloon Ground Station ϕ Elevation y x θ Azimuth x = y = z = 0 t = 0 t = 1 t = 2 t = 3 t = 4 Atmospheric Instrumentation M. D. Eastin

Upsondes – Weather Balloons Exposure Errors: Radiation Affects thermistors Direct exposure to solar radiation can produce a warm temperature error depending on the following: 1. Sensor Diameter (D) 2. Sensor Reflectivity 3. Ascent Rate (wB) The RS-92 platinum resistance thermistor is highly reflective with a 0.2 mm diameter Exposure Errors: Wet-bulbing Affects thermistors and hygristors Sensors remain wet for some time after emerging from a cloud. Cool temperature error due to evaporation Moist humidity error until heating cycle removes the excess moisture The RS-92 sensors are coated with a thin film of water-shedding material (like Rain-ex) that limits any sensor wetting (both in cloud and after emerging from cloud) Atmospheric Instrumentation M. D. Eastin

Downsondes – GPS Dropsondes Concept: Special radiosondes launched from high-altitude aircraft and descend at a controlled rate using a parachute Only deployed over oceans Only used during “targeted” observing efforts designed to improve high-impact forecasts for severe weather events or natural disasters Parachute Instrument Package Dropsonde Launch Tube in a NOAA Research Aircraft Atmospheric Instrumentation M. D. Eastin

Downsondes – GPS Dropsondes The Parachute: Square-cone chute deployed upon exit from launch tube Provides controlled and stable sonde descent without the “pendulum motion” common with circular parachutes Descent rate varies from 11–20 m/s in the troposphere Standard Dropsonde Specifications: Manufacturer / Model: Vaisala RD-94 Sensor Package Mass: 350 g Transmitter frequency: 400-406 MHz Max Telemetry Range: 325 km Max Deployable Airspeed: 250 knots Transmitter Antenna GPS Antenna PTH Sensors Temperature Sensor Humidity Sensors Pressure Atmospheric Instrumentation M. D. Eastin

Downsondes – GPS Dropsondes Standard Dropsonde Specifications: Sensor Type Accuracy Resolution Range Response Barometer Silicon Aneroid ±0.4 mb 0.1 mb 3 to 1080 mb < 1 s Thermistor Platinum Resistance ±0.2 °C 0.1 °C -90°C to +60°C < 2 s Hygristors Heated Capacitance ±2.0 % 1.0 % 0% to 100% < 20 s Winds GPS Positions ±0.5 m/s 0.1 m/s 0 to 150 m/s N / A Data Cycle: 2 Hz (PTH) Position Accuracy: ±5 m (horizontal) 4 Hz (winds) ±10 m (vertical) Descent Time: 15 min (from 14 km) 1. Wind Estimation → as with radiosondes, but 8 min (from 7 km) starting at drop location 2. Exposure Errors → same as for radiosondes Transmitter Antenna GPS Antenna PTH Sensors Temperature Sensor Humidity Sensors Pressure Atmospheric Instrumentation M. D. Eastin

Experimental Sounding Systems Rocket Sondes: Used to launch radiosondes into the upper level atmosphere (up to 120 km) where balloons cannot ascend Once the rocket reaches its maximum altitude, the sensor package descends using a square-cone parachute Used to study: Ozone Volcanic Emissions Radioactivity Earth’s Magnetic Field Cosmic Rays Mesospheric Chemistry Atmospheric Instrumentation M. D. Eastin

Experimental Sounding Systems Glider Sondes: Weather balloon transports instrumented glider to burst altitude and then the plane glides back to a designated point using an onboard GPS and flight navigation computer Reusable Low-cost alternative to the standard weather balloon packages often lost after each launch (total cost of $115,000 per year) “DataBird” manufactured by GPS-Boomerang: Still in development (field tests with prototypes) Expected to be useable for 50 flights Expected cost → $1000 per glider Expected savings → $100,000 per year Ascends to 20-35 km altitude in ~1 hour Descends in ~30 minutes at 3-4 m/s Measures pressure, temperature, humidity, winds using proprietary sensors Major remaining “hurdle” is air-space restrictions http://www.gpsboomerang.com/content/view/34/42/ Atmospheric Instrumentation M. D. Eastin

Experimental Sounding Systems Student Sonde: Still in development (field tests in progress) Inexpensive (volunteers – no health insurance) Major remaining “hurdle” is getting the student to survive at upper altitudes in the cold and low-oxygen environment Atmospheric Instrumentation M. D. Eastin

Summary Sounding Systems Review of Atmospheric Soundings “Upsondes” (Weather Balloons) Balloon Sensor Package Navigation / Telemetry System Wind Estimation Exposure Errors “Downsondes” (GPS Dropsondes) Experimental Sounding Systems Atmospheric Instrumentation M. D. Eastin

References Atmospheric Instrumentation M. D. Eastin Boire, G., D. C. Sutter, S. P. Pryor, and A.K. Brown, 1993: A low cost GS rawinsonde system. Preprints 8th Symposium on Meteorological Observations and Instrumentation, Anaheim, CA, American Meteorological Society, 23-24. Brock, F. V., and S. J. Richardson, 2001: Meteorological Measurement Systems, Oxford University Press, 290 pp. Finger, F. G., and F. J. Schmidlin, 1991: Upper-air measurements and instrumentation workshop. Bulletin of the American Meteorological Society, 72, 50-55. Harrison, R. G., 2015: Meteorological Instrumentation and Measurements, Wiley-Blackwell Publishing, 257 pp. Hock, T. F., and J. L. Franklin, 1999: The NCAR GPS dropwindsonde. Bulletin of the American Meteorological Society, 80, 407-420. Leurs, J.K., 1991: Estimating the temperature error of the radiosonde thermistor under different environmental conditions. Journal of Atmospheric and Oceanic Technology, 7, 882-895. Olsen, R. O., R. J. Okrasinski, and F. J. Schmidlin, 1991: Inter-comparison of upper air data derived from various radiosonde systems. Preprints 7th symposium on Meteorological Observations and Instrumentation, New Orleans, LA, American Meteorological Society, 232-236. Pratt, R. W., 1985: Review of radiosonde humidity and temperature errors. Journal of Atmospheric and Oceanic Technology, 2, 404-407. Reynolds, R. D., 1966: The effect of atmospheric lapse rates on balloon ascent rates. Journal of Applied Meteorology, 5, 537-541. Atmospheric Instrumentation M. D. Eastin